Adding upstream version 86.0.1.upstream/86.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 4445 insertions, 0 deletions

diff --git a/gfx/wr/swgl/src/gl.cc b/gfx/wr/swgl/src/gl.cc
new file mode 100644
index 0000000000..370d243b9a
--- /dev/null
+++ b/gfx/wr/swgl/src/gl.cc
@@ -0,0 +1,4445 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <assert.h>
+#include <stdio.h>
+#include <math.h>
+
+#ifdef __MACH__
+#  include <mach/mach.h>
+#  include <mach/mach_time.h>
+#else
+#  include <time.h>
+#endif
+
+#ifdef NDEBUG
+#  define debugf(...)
+#else
+#  define debugf(...) printf(__VA_ARGS__)
+#endif
+
+// #define PRINT_TIMINGS
+
+#ifdef _WIN32
+#  define ALWAYS_INLINE __forceinline
+#  define NO_INLINE __declspec(noinline)
+
+// Including Windows.h brings a huge amount of namespace polution so just
+// define a couple of things manually
+typedef int BOOL;
+#  define WINAPI __stdcall
+#  define DECLSPEC_IMPORT __declspec(dllimport)
+#  define WINBASEAPI DECLSPEC_IMPORT
+typedef unsigned long DWORD;
+typedef long LONG;
+typedef __int64 LONGLONG;
+#  define DUMMYSTRUCTNAME
+
+typedef union _LARGE_INTEGER {
+  struct {
+    DWORD LowPart;
+    LONG HighPart;
+  } DUMMYSTRUCTNAME;
+  struct {
+    DWORD LowPart;
+    LONG HighPart;
+  } u;
+  LONGLONG QuadPart;
+} LARGE_INTEGER;
+extern "C" {
+WINBASEAPI BOOL WINAPI
+QueryPerformanceCounter(LARGE_INTEGER* lpPerformanceCount);
+
+WINBASEAPI BOOL WINAPI QueryPerformanceFrequency(LARGE_INTEGER* lpFrequency);
+}
+
+#else
+#  define ALWAYS_INLINE __attribute__((always_inline)) inline
+#  define NO_INLINE __attribute__((noinline))
+#endif
+
+#define UNREACHABLE __builtin_unreachable()
+
+#define UNUSED __attribute__((unused))
+
+#define FALLTHROUGH __attribute__((fallthrough))
+
+#ifdef MOZILLA_CLIENT
+#  define IMPLICIT __attribute__((annotate("moz_implicit")))
+#else
+#  define IMPLICIT
+#endif
+
+#include "gl_defs.h"
+#include "glsl.h"
+#include "program.h"
+#include "texture.h"
+
+using namespace glsl;
+
+typedef ivec2_scalar IntPoint;
+
+struct IntRect {
+  int x0;
+  int y0;
+  int x1;
+  int y1;
+
+  IntRect() : x0(0), y0(0), x1(0), y1(0) {}
+  IntRect(int x0, int y0, int x1, int y1) : x0(x0), y0(y0), x1(x1), y1(y1) {}
+  IntRect(IntPoint origin, IntPoint size)
+      : x0(origin.x),
+        y0(origin.y),
+        x1(origin.x + size.x),
+        y1(origin.y + size.y) {}
+
+  int width() const { return x1 - x0; }
+  int height() const { return y1 - y0; }
+  bool is_empty() const { return width() <= 0 || height() <= 0; }
+
+  IntPoint origin() const { return IntPoint(x0, y0); }
+
+  bool same_size(const IntRect& o) const {
+    return width() == o.width() && height() == o.height();
+  }
+
+  bool contains(const IntRect& o) const {
+    return o.x0 >= x0 && o.y0 >= y0 && o.x1 <= x1 && o.y1 <= y1;
+  }
+
+  IntRect& intersect(const IntRect& o) {
+    x0 = max(x0, o.x0);
+    y0 = max(y0, o.y0);
+    x1 = min(x1, o.x1);
+    y1 = min(y1, o.y1);
+    return *this;
+  }
+
+  IntRect intersection(const IntRect& o) {
+    IntRect result = *this;
+    result.intersect(o);
+    return result;
+  }
+
+  // Scale from source-space to dest-space, optionally rounding inward
+  IntRect& scale(int srcWidth, int srcHeight, int dstWidth, int dstHeight,
+                 bool roundIn = false) {
+    x0 = (x0 * dstWidth + (roundIn ? srcWidth - 1 : 0)) / srcWidth;
+    y0 = (y0 * dstHeight + (roundIn ? srcHeight - 1 : 0)) / srcHeight;
+    x1 = (x1 * dstWidth) / srcWidth;
+    y1 = (y1 * dstHeight) / srcHeight;
+    return *this;
+  }
+
+  // Flip the rect's Y coords around inflection point at Y=offset
+  void invert_y(int offset) {
+    y0 = offset - y0;
+    y1 = offset - y1;
+    swap(y0, y1);
+  }
+
+  IntRect& offset(const IntPoint& o) {
+    x0 += o.x;
+    y0 += o.y;
+    x1 += o.x;
+    y1 += o.y;
+    return *this;
+  }
+
+  IntRect operator+(const IntPoint& o) const {
+    return IntRect(*this).offset(o);
+  }
+  IntRect operator-(const IntPoint& o) const {
+    return IntRect(*this).offset(-o);
+  }
+};
+
+struct VertexAttrib {
+  size_t size = 0;  // in bytes
+  GLenum type = 0;
+  bool normalized = false;
+  GLsizei stride = 0;
+  GLuint offset = 0;
+  bool enabled = false;
+  GLuint divisor = 0;
+  int vertex_array = 0;
+  int vertex_buffer = 0;
+  char* buf = nullptr;  // XXX: this can easily dangle
+  size_t buf_size = 0;  // this will let us bounds check
+};
+
+static int bytes_for_internal_format(GLenum internal_format) {
+  switch (internal_format) {
+    case GL_RGBA32F:
+      return 4 * 4;
+    case GL_RGBA32I:
+      return 4 * 4;
+    case GL_RGBA8:
+    case GL_BGRA8:
+    case GL_RGBA:
+      return 4;
+    case GL_R8:
+    case GL_RED:
+      return 1;
+    case GL_RG8:
+    case GL_RG:
+      return 2;
+    case GL_DEPTH_COMPONENT:
+    case GL_DEPTH_COMPONENT16:
+    case GL_DEPTH_COMPONENT24:
+    case GL_DEPTH_COMPONENT32:
+      return 4;
+    case GL_RGB_RAW_422_APPLE:
+      return 2;
+    case GL_R16:
+      return 2;
+    default:
+      debugf("internal format: %x\n", internal_format);
+      assert(0);
+      return 0;
+  }
+}
+
+static inline int aligned_stride(int row_bytes) { return (row_bytes + 3) & ~3; }
+
+static TextureFormat gl_format_to_texture_format(int type) {
+  switch (type) {
+    case GL_RGBA32F:
+      return TextureFormat::RGBA32F;
+    case GL_RGBA32I:
+      return TextureFormat::RGBA32I;
+    case GL_RGBA8:
+      return TextureFormat::RGBA8;
+    case GL_R8:
+      return TextureFormat::R8;
+    case GL_RG8:
+      return TextureFormat::RG8;
+    case GL_R16:
+      return TextureFormat::R16;
+    case GL_RGB_RAW_422_APPLE:
+      return TextureFormat::YUV422;
+    default:
+      assert(0);
+      return TextureFormat::RGBA8;
+  }
+}
+
+struct Query {
+  uint64_t value = 0;
+};
+
+struct Buffer {
+  char* buf = nullptr;
+  size_t size = 0;
+  size_t capacity = 0;
+
+  bool allocate(size_t new_size) {
+    // If the size remains unchanged, don't allocate anything.
+    if (new_size == size) {
+      return false;
+    }
+    // If the new size is within the existing capacity of the buffer, just
+    // reuse the existing buffer.
+    if (new_size <= capacity) {
+      size = new_size;
+      return true;
+    }
+    // Otherwise we need to reallocate the buffer to hold up to the requested
+    // larger size.
+    char* new_buf = (char*)realloc(buf, new_size);
+    assert(new_buf);
+    if (!new_buf) {
+      // If we fail, null out the buffer rather than leave around the old
+      // allocation state.
+      cleanup();
+      return false;
+    }
+    // The reallocation succeeded, so install the buffer.
+    buf = new_buf;
+    size = new_size;
+    capacity = new_size;
+    return true;
+  }
+
+  void cleanup() {
+    if (buf) {
+      free(buf);
+      buf = nullptr;
+      size = 0;
+      capacity = 0;
+    }
+  }
+
+  ~Buffer() { cleanup(); }
+};
+
+struct Framebuffer {
+  GLuint color_attachment = 0;
+  GLint layer = 0;
+  GLuint depth_attachment = 0;
+};
+
+struct Renderbuffer {
+  GLuint texture = 0;
+
+  void on_erase();
+};
+
+TextureFilter gl_filter_to_texture_filter(int type) {
+  switch (type) {
+    case GL_NEAREST:
+      return TextureFilter::NEAREST;
+    case GL_NEAREST_MIPMAP_LINEAR:
+      return TextureFilter::NEAREST;
+    case GL_NEAREST_MIPMAP_NEAREST:
+      return TextureFilter::NEAREST;
+    case GL_LINEAR:
+      return TextureFilter::LINEAR;
+    case GL_LINEAR_MIPMAP_LINEAR:
+      return TextureFilter::LINEAR;
+    case GL_LINEAR_MIPMAP_NEAREST:
+      return TextureFilter::LINEAR;
+    default:
+      assert(0);
+      return TextureFilter::NEAREST;
+  }
+}
+
+// The SWGL depth buffer is roughly organized as a span buffer where each row
+// of the depth buffer is a list of spans, and each span has a constant depth
+// and a run length (represented by DepthRun). The span from start..start+count
+// is placed directly at that start index in the row's array of runs, so that
+// there is no need to explicitly record the start index at all. This also
+// avoids the need to move items around in the run array to manage insertions
+// since space is implicitly always available for a run between any two
+// pre-existing runs. Linkage from one run to the next is implicitly defined by
+// the count, so if a run exists from start..start+count, the next run will
+// implicitly pick up right at index start+count where that preceding run left
+// off. All of the DepthRun items that are after the head of the run can remain
+// uninitialized until the run needs to be split and a new run needs to start
+// somewhere in between.
+// For uses like perspective-correct rasterization or with a discard mask, a
+// run is not an efficient representation, and it is more beneficial to have
+// a flattened array of individual depth samples that can be masked off easily.
+// To support this case, the first run in a given row's run array may have a
+// zero count, signaling that this entire row is flattened. Critically, the
+// depth and count fields in DepthRun are ordered (endian-dependently) so that
+// the DepthRun struct can be interpreted as a sign-extended int32_t depth. It
+// is then possible to just treat the entire row as an array of int32_t depth
+// samples that can be processed with SIMD comparisons, since the count field
+// behaves as just the sign-extension of the depth field.
+// When a depth buffer is cleared, each row is initialized to a single run
+// spanning the entire row. In the normal case, the depth buffer will continue
+// to manage itself as a list of runs. If perspective or discard is used for
+// a given row, the row will be converted to the flattened representation to
+// support it, after which it will only ever revert back to runs if the depth
+// buffer is cleared.
+struct DepthRun {
+  // Ensure that depth always occupies the LSB and count the MSB so that we
+  // can sign-extend depth just by setting count to zero, marking it flat.
+  // When count is non-zero, then this is interpreted as an actual run and
+  // depth is read in isolation.
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+  uint16_t depth;
+  uint16_t count;
+#else
+  uint16_t count;
+  uint16_t depth;
+#endif
+
+  DepthRun() = default;
+  DepthRun(uint16_t depth, uint16_t count) : depth(depth), count(count) {}
+
+  // If count is zero, this is actually a flat depth sample rather than a run.
+  bool is_flat() const { return !count; }
+
+  // Compare a source depth from rasterization with a stored depth value.
+  template <int FUNC>
+  ALWAYS_INLINE bool compare(uint16_t src) const {
+    switch (FUNC) {
+      case GL_LEQUAL:
+        return src <= depth;
+      case GL_LESS:
+        return src < depth;
+      case GL_ALWAYS:
+        return true;
+      default:
+        assert(false);
+        return false;
+    }
+  }
+};
+
+// A cursor for reading and modifying a row's depth run array. It locates
+// and iterates through a desired span within all the runs, testing if
+// the depth of this span passes or fails the depth test against existing
+// runs. If desired, new runs may be inserted to represent depth occlusion
+// from this span in the run array.
+struct DepthCursor {
+  // Current position of run the cursor has advanced to.
+  DepthRun* cur = nullptr;
+  // The start of the remaining potential samples in the desired span.
+  DepthRun* start = nullptr;
+  // The end of the potential samples in the desired span.
+  DepthRun* end = nullptr;
+
+  DepthCursor() = default;
+
+  // Construct a cursor with runs for a given row's run array and the bounds
+  // of the span we wish to iterate within it.
+  DepthCursor(DepthRun* runs, int num_runs, int span_offset, int span_count)
+      : cur(runs), start(&runs[span_offset]), end(start + span_count) {
+    // This cursor should never iterate over flat runs
+    assert(!runs->is_flat());
+    DepthRun* end_runs = &runs[num_runs];
+    // Clamp end of span to end of row
+    if (end > end_runs) {
+      end = end_runs;
+    }
+    // If the span starts past the end of the row, just advance immediately
+    // to it to signal that we're done.
+    if (start >= end_runs) {
+      cur = end_runs;
+      start = end_runs;
+      return;
+    }
+    // Otherwise, find the first depth run that contains the start of the span.
+    // If the span starts after the given run, then we need to keep searching
+    // through the row to find an appropriate run. The check above already
+    // guaranteed that the span starts within the row's runs, and the search
+    // won't fall off the end.
+    for (;;) {
+      assert(cur < end);
+      DepthRun* next = cur + cur->count;
+      if (start < next) {
+        break;
+      }
+      cur = next;
+    }
+  }
+
+  // The cursor is valid if the current position is at the end or if the run
+  // contains the start position.
+  bool valid() const {
+    return cur >= end || (cur <= start && start < cur + cur->count);
+  }
+
+  // Skip past any initial runs that fail the depth test. If we find a run that
+  // would pass, then return the accumulated length between where we started
+  // and that position. Otherwise, if we fall off the end, return -1 to signal
+  // that there are no more passed runs at the end of this failed region and
+  // so it is safe for the caller to stop processing any more regions in this
+  // row.
+  template <int FUNC>
+  int skip_failed(uint16_t val) {
+    assert(valid());
+    DepthRun* prev = start;
+    while (cur < end) {
+      if (cur->compare<FUNC>(val)) {
+        return start - prev;
+      }
+      cur += cur->count;
+      start = cur;
+    }
+    return -1;
+  }
+
+  // Helper to convert function parameters into template parameters to hoist
+  // some checks out of inner loops.
+  ALWAYS_INLINE int skip_failed(uint16_t val, GLenum func) {
+    switch (func) {
+      case GL_LEQUAL:
+        return skip_failed<GL_LEQUAL>(val);
+      case GL_LESS:
+        return skip_failed<GL_LESS>(val);
+      default:
+        assert(false);
+        return -1;
+    }
+  }
+
+  // Find a region of runs that passes the depth test. It is assumed the caller
+  // has called skip_failed first to skip past any runs that failed the depth
+  // test. This stops when it finds a run that fails the depth test or we fall
+  // off the end of the row. If the write mask is enabled, this will insert runs
+  // to represent this new region that passed the depth test. The length of the
+  // region is returned.
+  template <int FUNC, bool MASK>
+  int check_passed(uint16_t val) {
+    assert(valid());
+    DepthRun* prev = cur;
+    while (cur < end) {
+      if (!cur->compare<FUNC>(val)) {
+        break;
+      }
+      DepthRun* next = cur + cur->count;
+      if (next > end) {
+        if (MASK) {
+          // Chop the current run where the end of the span falls, making a new
+          // run from the end of the span till the next run. The beginning of
+          // the current run will be folded into the run from the start of the
+          // passed region before returning below.
+          *end = DepthRun(cur->depth, next - end);
+        }
+        // If the next run starts past the end, then just advance the current
+        // run to the end to signal that we're now at the end of the row.
+        next = end;
+      }
+      cur = next;
+    }
+    // If we haven't advanced past the start of the span region, then we found
+    // nothing that passed.
+    if (cur <= start) {
+      return 0;
+    }
+    // If 'end' fell within the middle of a passing run, then 'cur' will end up
+    // pointing at the new partial run created at 'end' where the passing run
+    // was split to accommodate starting in the middle. The preceding runs will
+    // be fixed below to properly join with this new split.
+    int passed = cur - start;
+    if (MASK) {
+      // If the search started from a run before the start of the span, then
+      // edit that run to meet up with the start.
+      if (prev < start) {
+        prev->count = start - prev;
+      }
+      // Create a new run for the entirety of the passed samples.
+      *start = DepthRun(val, passed);
+    }
+    start = cur;
+    return passed;
+  }
+
+  // Helper to convert function parameters into template parameters to hoist
+  // some checks out of inner loops.
+  template <bool MASK>
+  ALWAYS_INLINE int check_passed(uint16_t val, GLenum func) {
+    switch (func) {
+      case GL_LEQUAL:
+        return check_passed<GL_LEQUAL, MASK>(val);
+      case GL_LESS:
+        return check_passed<GL_LESS, MASK>(val);
+      default:
+        assert(false);
+        return 0;
+    }
+  }
+
+  ALWAYS_INLINE int check_passed(uint16_t val, GLenum func, bool mask) {
+    return mask ? check_passed<true>(val, func)
+                : check_passed<false>(val, func);
+  }
+
+  // Fill a region of runs with a given depth value, bypassing any depth test.
+  ALWAYS_INLINE void fill(uint16_t depth) {
+    check_passed<GL_ALWAYS, true>(depth);
+  }
+};
+
+struct Texture {
+  GLenum internal_format = 0;
+  int width = 0;
+  int height = 0;
+  int depth = 0;
+  char* buf = nullptr;
+  size_t buf_size = 0;
+  uint32_t buf_stride = 0;
+  uint8_t buf_bpp = 0;
+  GLenum min_filter = GL_NEAREST;
+  GLenum mag_filter = GL_LINEAR;
+  // The number of active locks on this texture. If this texture has any active
+  // locks, we need to disallow modifying or destroying the texture as it may
+  // be accessed by other threads where modifications could lead to races.
+  int32_t locked = 0;
+  // When used as an attachment of a framebuffer, rendering to the texture
+  // behaves as if it is located at the given offset such that the offset is
+  // subtracted from all transformed vertexes after the viewport is applied.
+  IntPoint offset;
+
+  enum FLAGS {
+    // If the buffer is internally-allocated by SWGL
+    SHOULD_FREE = 1 << 1,
+    // If the buffer has been cleared to initialize it. Currently this is only
+    // utilized by depth buffers which need to know when depth runs have reset
+    // to a valid row state. When unset, the depth runs may contain garbage.
+    CLEARED = 1 << 2,
+  };
+  int flags = SHOULD_FREE;
+  bool should_free() const { return bool(flags & SHOULD_FREE); }
+  bool cleared() const { return bool(flags & CLEARED); }
+
+  void set_flag(int flag, bool val) {
+    if (val) {
+      flags |= flag;
+    } else {
+      flags &= ~flag;
+    }
+  }
+  void set_should_free(bool val) {
+    // buf must be null before SHOULD_FREE can be safely toggled. Otherwise, we
+    // might accidentally mistakenly realloc an externally allocated buffer as
+    // if it were an internally allocated one.
+    assert(!buf);
+    set_flag(SHOULD_FREE, val);
+  }
+  void set_cleared(bool val) { set_flag(CLEARED, val); }
+
+  // Delayed-clearing state. When a clear of an FB is requested, we don't
+  // immediately clear each row, as the rows may be subsequently overwritten
+  // by draw calls, allowing us to skip the work of clearing the affected rows
+  // either fully or partially. Instead, we keep a bit vector of rows that need
+  // to be cleared later and save the value they need to be cleared with so
+  // that we can clear these rows individually when they are touched by draws.
+  // This currently only works for 2D textures, but not on texture arrays.
+  int delay_clear = 0;
+  uint32_t clear_val = 0;
+  uint32_t* cleared_rows = nullptr;
+
+  void init_depth_runs(uint16_t z);
+  void fill_depth_runs(uint16_t z);
+
+  void enable_delayed_clear(uint32_t val) {
+    delay_clear = height;
+    clear_val = val;
+    if (!cleared_rows) {
+      cleared_rows = new uint32_t[(height + 31) / 32];
+    }
+    memset(cleared_rows, 0, ((height + 31) / 32) * sizeof(uint32_t));
+    if (height & 31) {
+      cleared_rows[height / 32] = ~0U << (height & 31);
+    }
+  }
+
+  void disable_delayed_clear() {
+    if (cleared_rows) {
+      delete[] cleared_rows;
+      cleared_rows = nullptr;
+      delay_clear = 0;
+    }
+  }
+
+  int bpp() const { return buf_bpp; }
+  void set_bpp() { buf_bpp = bytes_for_internal_format(internal_format); }
+
+  size_t stride() const { return buf_stride; }
+  void set_stride() { buf_stride = aligned_stride(buf_bpp * width); }
+
+  // Set an external backing buffer of this texture.
+  void set_buffer(void* new_buf, size_t new_stride) {
+    assert(!should_free());
+    // Ensure that the supplied stride is at least as big as the internally
+    // calculated aligned stride.
+    set_bpp();
+    set_stride();
+    assert(new_stride >= buf_stride);
+
+    buf = (char*)new_buf;
+    buf_size = 0;
+    buf_stride = new_stride;
+  }
+
+  bool allocate(bool force = false, int min_width = 0, int min_height = 0) {
+    assert(!locked);  // Locked textures shouldn't be reallocated
+    // If we get here, some GL API call that invalidates the texture was used.
+    // Mark the buffer as not-cleared to signal this.
+    set_cleared(false);
+    // Check if there is either no buffer currently or if we forced validation
+    // of the buffer size because some dimension might have changed.
+    if ((!buf || force) && should_free()) {
+      // Initialize the buffer's BPP and stride, since they may have changed.
+      set_bpp();
+      set_stride();
+      // Compute new size based on the maximum potential stride, rather than
+      // the current stride, to hopefully avoid reallocations when size would
+      // otherwise change too much...
+      size_t max_stride = max(buf_stride, aligned_stride(buf_bpp * min_width));
+      size_t size = max_stride * max(height, min_height) * max(depth, 1);
+      if ((!buf && size > 0) || size > buf_size) {
+        // Allocate with a SIMD register-sized tail of padding at the end so we
+        // can safely read or write past the end of the texture with SIMD ops.
+        // Currently only the flat Z-buffer texture needs this padding due to
+        // full-register loads and stores in check_depth and discard_depth. In
+        // case some code in the future accidentally uses a linear filter on a
+        // texture with less than 2 pixels per row, we also add this padding
+        // just to be safe. All other texture types and use-cases should be
+        // safe to omit padding.
+        size_t padding =
+            internal_format == GL_DEPTH_COMPONENT16 || max(width, min_width) < 2
+                ? sizeof(Float)
+                : 0;
+        char* new_buf = (char*)realloc(buf, size + padding);
+        assert(new_buf);
+        if (new_buf) {
+          // Successfully reallocated the buffer, so go ahead and set it.
+          buf = new_buf;
+          buf_size = size;
+          return true;
+        }
+        // Allocation failed, so ensure we don't leave stale buffer state.
+        cleanup();
+      }
+    }
+    // Nothing changed...
+    return false;
+  }
+
+  void cleanup() {
+    assert(!locked);  // Locked textures shouldn't be destroyed
+    if (buf) {
+      // If we need to toggle SHOULD_FREE state, ensure that buf is nulled out,
+      // regardless of whether we internally allocated it. This will prevent us
+      // from wrongly treating buf as having been internally allocated for when
+      // we go to realloc if it actually was externally allocted.
+      if (should_free()) {
+        free(buf);
+      }
+      buf = nullptr;
+      buf_size = 0;
+      buf_bpp = 0;
+      buf_stride = 0;
+    }
+    disable_delayed_clear();
+  }
+
+  ~Texture() { cleanup(); }
+
+  IntRect bounds() const { return IntRect{0, 0, width, height}; }
+  IntRect offset_bounds() const { return bounds() + offset; }
+
+  // Find the valid sampling bounds relative to the requested region
+  IntRect sample_bounds(const IntRect& req, bool invertY = false) const {
+    IntRect bb = bounds().intersect(req) - req.origin();
+    if (invertY) bb.invert_y(req.height());
+    return bb;
+  }
+
+  // Get a pointer for sampling at the given offset
+  char* sample_ptr(int x, int y, int z = 0) const {
+    return buf + (height * z + y) * stride() + x * bpp();
+  }
+
+  // Get a pointer for sampling the requested region and limit to the provided
+  // sampling bounds
+  char* sample_ptr(const IntRect& req, const IntRect& bounds, int z,
+                   bool invertY = false) const {
+    // Offset the sample pointer by the clamped bounds
+    int x = req.x0 + bounds.x0;
+    // Invert the Y offset if necessary
+    int y = invertY ? req.y1 - 1 - bounds.y0 : req.y0 + bounds.y0;
+    return sample_ptr(x, y, z);
+  }
+};
+
+// The last vertex attribute is reserved as a null attribute in case a vertex
+// attribute is used without being set.
+#define MAX_ATTRIBS 17
+#define NULL_ATTRIB 16
+struct VertexArray {
+  VertexAttrib attribs[MAX_ATTRIBS];
+  int max_attrib = -1;
+  // The GL spec defines element array buffer binding to be part of VAO state.
+  GLuint element_array_buffer_binding = 0;
+
+  void validate();
+};
+
+struct Shader {
+  GLenum type = 0;
+  ProgramLoader loader = nullptr;
+};
+
+struct Program {
+  ProgramImpl* impl = nullptr;
+  VertexShaderImpl* vert_impl = nullptr;
+  FragmentShaderImpl* frag_impl = nullptr;
+  bool deleted = false;
+
+  ~Program() { delete impl; }
+};
+
+// clang-format off
+// for GL defines to fully expand
+#define CONCAT_KEY(prefix, x, y, z, w, ...) prefix##x##y##z##w
+#define BLEND_KEY(...) CONCAT_KEY(BLEND_, __VA_ARGS__, 0, 0)
+#define MASK_BLEND_KEY(...) CONCAT_KEY(MASK_BLEND_, __VA_ARGS__, 0, 0)
+#define FOR_EACH_BLEND_KEY(macro)                                              \
+  macro(GL_ONE, GL_ZERO, 0, 0)                                                 \
+  macro(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE, GL_ONE_MINUS_SRC_ALPHA)  \
+  macro(GL_ONE, GL_ONE_MINUS_SRC_ALPHA, 0, 0)                                  \
+  macro(GL_ZERO, GL_ONE_MINUS_SRC_COLOR, 0, 0)                                 \
+  macro(GL_ZERO, GL_ONE_MINUS_SRC_COLOR, GL_ZERO, GL_ONE)                      \
+  macro(GL_ZERO, GL_ONE_MINUS_SRC_ALPHA, 0, 0)                                 \
+  macro(GL_ZERO, GL_SRC_COLOR, 0, 0)                                           \
+  macro(GL_ONE, GL_ONE, 0, 0)                                                  \
+  macro(GL_ONE, GL_ONE, GL_ONE, GL_ONE_MINUS_SRC_ALPHA)                        \
+  macro(GL_ONE_MINUS_DST_ALPHA, GL_ONE, GL_ZERO, GL_ONE)                       \
+  macro(GL_CONSTANT_COLOR, GL_ONE_MINUS_SRC_COLOR, 0, 0)                       \
+  macro(GL_ONE, GL_ONE_MINUS_SRC1_COLOR, 0, 0)
+
+#define DEFINE_BLEND_KEY(...) BLEND_KEY(__VA_ARGS__),
+#define DEFINE_MASK_BLEND_KEY(...) MASK_BLEND_KEY(__VA_ARGS__),
+enum BlendKey : uint8_t {
+  FOR_EACH_BLEND_KEY(DEFINE_BLEND_KEY)
+  FOR_EACH_BLEND_KEY(DEFINE_MASK_BLEND_KEY)
+  BLEND_KEY_NONE = BLEND_KEY(GL_ONE, GL_ZERO),
+  MASK_BLEND_KEY_NONE = MASK_BLEND_KEY(GL_ONE, GL_ZERO)
+};
+// clang-format on
+
+const size_t MAX_TEXTURE_UNITS = 16;
+
+template <typename T>
+static inline bool unlink(T& binding, T n) {
+  if (binding == n) {
+    binding = 0;
+    return true;
+  }
+  return false;
+}
+
+template <typename O>
+struct ObjectStore {
+  O** objects = nullptr;
+  size_t size = 0;
+  // reserve object 0 as null
+  size_t first_free = 1;
+  O invalid;
+
+  ~ObjectStore() {
+    if (objects) {
+      for (size_t i = 0; i < size; i++) delete objects[i];
+      free(objects);
+    }
+  }
+
+  bool grow(size_t i) {
+    size_t new_size = size ? size : 8;
+    while (new_size <= i) new_size += new_size / 2;
+    O** new_objects = (O**)realloc(objects, new_size * sizeof(O*));
+    assert(new_objects);
+    if (!new_objects) return false;
+    while (size < new_size) new_objects[size++] = nullptr;
+    objects = new_objects;
+    return true;
+  }
+
+  void insert(size_t i, const O& o) {
+    if (i >= size && !grow(i)) return;
+    if (!objects[i]) objects[i] = new O(o);
+  }
+
+  size_t next_free() {
+    size_t i = first_free;
+    while (i < size && objects[i]) i++;
+    first_free = i;
+    return i;
+  }
+
+  size_t insert(const O& o = O()) {
+    size_t i = next_free();
+    insert(i, o);
+    return i;
+  }
+
+  O& operator[](size_t i) {
+    insert(i, O());
+    return i < size ? *objects[i] : invalid;
+  }
+
+  O* find(size_t i) const { return i < size ? objects[i] : nullptr; }
+
+  template <typename T>
+  void on_erase(T*, ...) {}
+  template <typename T>
+  void on_erase(T* o, decltype(&T::on_erase)) {
+    o->on_erase();
+  }
+
+  bool erase(size_t i) {
+    if (i < size && objects[i]) {
+      on_erase(objects[i], nullptr);
+      delete objects[i];
+      objects[i] = nullptr;
+      if (i < first_free) first_free = i;
+      return true;
+    }
+    return false;
+  }
+
+  O** begin() const { return objects; }
+  O** end() const { return &objects[size]; }
+};
+
+struct Context {
+  int32_t references = 1;
+
+  ObjectStore<Query> queries;
+  ObjectStore<Buffer> buffers;
+  ObjectStore<Texture> textures;
+  ObjectStore<VertexArray> vertex_arrays;
+  ObjectStore<Framebuffer> framebuffers;
+  ObjectStore<Renderbuffer> renderbuffers;
+  ObjectStore<Shader> shaders;
+  ObjectStore<Program> programs;
+
+  IntRect viewport = {0, 0, 0, 0};
+
+  bool blend = false;
+  GLenum blendfunc_srgb = GL_ONE;
+  GLenum blendfunc_drgb = GL_ZERO;
+  GLenum blendfunc_sa = GL_ONE;
+  GLenum blendfunc_da = GL_ZERO;
+  GLenum blend_equation = GL_FUNC_ADD;
+  V8<uint16_t> blendcolor = 0;
+  BlendKey blend_key = BLEND_KEY_NONE;
+
+  bool depthtest = false;
+  bool depthmask = true;
+  GLenum depthfunc = GL_LESS;
+
+  bool scissortest = false;
+  IntRect scissor = {0, 0, 0, 0};
+
+  uint32_t clearcolor = 0;
+  GLdouble cleardepth = 1;
+
+  int unpack_row_length = 0;
+
+  int shaded_rows = 0;
+  int shaded_pixels = 0;
+
+  struct TextureUnit {
+    GLuint texture_2d_binding = 0;
+    GLuint texture_3d_binding = 0;
+    GLuint texture_2d_array_binding = 0;
+    GLuint texture_rectangle_binding = 0;
+
+    void unlink(GLuint n) {
+      ::unlink(texture_2d_binding, n);
+      ::unlink(texture_3d_binding, n);
+      ::unlink(texture_2d_array_binding, n);
+      ::unlink(texture_rectangle_binding, n);
+    }
+  };
+  TextureUnit texture_units[MAX_TEXTURE_UNITS];
+  int active_texture_unit = 0;
+
+  GLuint current_program = 0;
+
+  GLuint current_vertex_array = 0;
+  bool validate_vertex_array = true;
+
+  GLuint pixel_pack_buffer_binding = 0;
+  GLuint pixel_unpack_buffer_binding = 0;
+  GLuint array_buffer_binding = 0;
+  GLuint time_elapsed_query = 0;
+  GLuint samples_passed_query = 0;
+  GLuint renderbuffer_binding = 0;
+  GLuint draw_framebuffer_binding = 0;
+  GLuint read_framebuffer_binding = 0;
+  GLuint unknown_binding = 0;
+
+  GLuint& get_binding(GLenum name) {
+    switch (name) {
+      case GL_PIXEL_PACK_BUFFER:
+        return pixel_pack_buffer_binding;
+      case GL_PIXEL_UNPACK_BUFFER:
+        return pixel_unpack_buffer_binding;
+      case GL_ARRAY_BUFFER:
+        return array_buffer_binding;
+      case GL_ELEMENT_ARRAY_BUFFER:
+        return vertex_arrays[current_vertex_array].element_array_buffer_binding;
+      case GL_TEXTURE_2D:
+        return texture_units[active_texture_unit].texture_2d_binding;
+      case GL_TEXTURE_2D_ARRAY:
+        return texture_units[active_texture_unit].texture_2d_array_binding;
+      case GL_TEXTURE_3D:
+        return texture_units[active_texture_unit].texture_3d_binding;
+      case GL_TEXTURE_RECTANGLE:
+        return texture_units[active_texture_unit].texture_rectangle_binding;
+      case GL_TIME_ELAPSED:
+        return time_elapsed_query;
+      case GL_SAMPLES_PASSED:
+        return samples_passed_query;
+      case GL_RENDERBUFFER:
+        return renderbuffer_binding;
+      case GL_DRAW_FRAMEBUFFER:
+        return draw_framebuffer_binding;
+      case GL_READ_FRAMEBUFFER:
+        return read_framebuffer_binding;
+      default:
+        debugf("unknown binding %x\n", name);
+        assert(false);
+        return unknown_binding;
+    }
+  }
+
+  Texture& get_texture(sampler2D, int unit) {
+    return textures[texture_units[unit].texture_2d_binding];
+  }
+
+  Texture& get_texture(isampler2D, int unit) {
+    return textures[texture_units[unit].texture_2d_binding];
+  }
+
+  Texture& get_texture(sampler2DArray, int unit) {
+    return textures[texture_units[unit].texture_2d_array_binding];
+  }
+
+  Texture& get_texture(sampler2DRect, int unit) {
+    return textures[texture_units[unit].texture_rectangle_binding];
+  }
+
+  IntRect apply_scissor(IntRect bb,
+                        const IntPoint& origin = IntPoint(0, 0)) const {
+    return scissortest ? bb.intersect(scissor - origin) : bb;
+  }
+
+  IntRect apply_scissor(const Texture& t) const {
+    return apply_scissor(t.bounds(), t.offset);
+  }
+};
+static Context* ctx = nullptr;
+static VertexShaderImpl* vertex_shader = nullptr;
+static FragmentShaderImpl* fragment_shader = nullptr;
+static BlendKey blend_key = BLEND_KEY_NONE;
+
+static void prepare_texture(Texture& t, const IntRect* skip = nullptr);
+
+template <typename S>
+static inline void init_depth(S* s, Texture& t) {
+  s->depth = max(t.depth, 1);
+  s->height_stride = s->stride * t.height;
+}
+
+template <typename S>
+static inline void init_filter(S* s, Texture& t) {
+  // If the width is not at least 2 pixels, then we can't safely sample the end
+  // of the row with a linear filter. In that case, just punt to using nearest
+  // filtering instead.
+  s->filter = t.width >= 2 ? gl_filter_to_texture_filter(t.mag_filter)
+                           : TextureFilter::NEAREST;
+}
+
+template <typename S>
+static inline void init_sampler(S* s, Texture& t) {
+  prepare_texture(t);
+  s->width = t.width;
+  s->height = t.height;
+  s->stride = t.stride();
+  int bpp = t.bpp();
+  if (bpp >= 4)
+    s->stride /= 4;
+  else if (bpp == 2)
+    s->stride /= 2;
+  else
+    assert(bpp == 1);
+  // Use uint32_t* for easier sampling, but need to cast to uint8_t* or
+  // uint16_t* for formats with bpp < 4.
+  s->buf = (uint32_t*)t.buf;
+  s->format = gl_format_to_texture_format(t.internal_format);
+}
+
+template <typename S>
+static inline void null_sampler(S* s) {
+  // For null texture data, just make the sampler provide a 1x1 buffer that is
+  // transparent black. Ensure buffer holds at least a SIMD vector of zero data
+  // for SIMD padding of unaligned loads.
+  static const uint32_t zeroBuf[sizeof(Float) / sizeof(uint32_t)] = {0};
+  s->width = 1;
+  s->height = 1;
+  s->stride = s->width;
+  s->buf = (uint32_t*)zeroBuf;
+  s->format = TextureFormat::RGBA8;
+}
+
+template <typename S>
+static inline void null_filter(S* s) {
+  s->filter = TextureFilter::NEAREST;
+}
+
+template <typename S>
+static inline void null_depth(S* s) {
+  s->depth = 1;
+  s->height_stride = s->stride;
+}
+
+template <typename S>
+S* lookup_sampler(S* s, int texture) {
+  Texture& t = ctx->get_texture(s, texture);
+  if (!t.buf) {
+    null_sampler(s);
+    null_filter(s);
+  } else {
+    init_sampler(s, t);
+    init_filter(s, t);
+  }
+  return s;
+}
+
+template <typename S>
+S* lookup_isampler(S* s, int texture) {
+  Texture& t = ctx->get_texture(s, texture);
+  if (!t.buf) {
+    null_sampler(s);
+  } else {
+    init_sampler(s, t);
+  }
+  return s;
+}
+
+template <typename S>
+S* lookup_sampler_array(S* s, int texture) {
+  Texture& t = ctx->get_texture(s, texture);
+  if (!t.buf) {
+    null_sampler(s);
+    null_depth(s);
+    null_filter(s);
+  } else {
+    init_sampler(s, t);
+    init_depth(s, t);
+    init_filter(s, t);
+  }
+  return s;
+}
+
+int bytes_per_type(GLenum type) {
+  switch (type) {
+    case GL_INT:
+      return 4;
+    case GL_FLOAT:
+      return 4;
+    case GL_UNSIGNED_SHORT:
+      return 2;
+    case GL_UNSIGNED_BYTE:
+      return 1;
+    default:
+      assert(0);
+      return 0;
+  }
+}
+
+template <typename S, typename C>
+static inline S expand_attrib(const char* buf, size_t size, bool normalized) {
+  typedef typename ElementType<S>::ty elem_type;
+  S scalar = {0};
+  const C* src = reinterpret_cast<const C*>(buf);
+  if (normalized) {
+    const float scale = 1.0f / ((1 << (8 * sizeof(C))) - 1);
+    for (size_t i = 0; i < size / sizeof(C); i++) {
+      put_nth_component(scalar, i, elem_type(src[i]) * scale);
+    }
+  } else {
+    for (size_t i = 0; i < size / sizeof(C); i++) {
+      put_nth_component(scalar, i, elem_type(src[i]));
+    }
+  }
+  return scalar;
+}
+
+template <typename S>
+static inline S load_attrib_scalar(VertexAttrib& va, const char* src) {
+  if (sizeof(S) <= va.size) {
+    return *reinterpret_cast<const S*>(src);
+  }
+  if (va.type == GL_UNSIGNED_SHORT) {
+    return expand_attrib<S, uint16_t>(src, va.size, va.normalized);
+  }
+  if (va.type == GL_UNSIGNED_BYTE) {
+    return expand_attrib<S, uint8_t>(src, va.size, va.normalized);
+  }
+  assert(sizeof(typename ElementType<S>::ty) == bytes_per_type(va.type));
+  S scalar = {0};
+  memcpy(&scalar, src, va.size);
+  return scalar;
+}
+
+template <typename T>
+void load_attrib(T& attrib, VertexAttrib& va, uint32_t start, int instance,
+                 int count) {
+  typedef decltype(force_scalar(attrib)) scalar_type;
+  if (!va.enabled) {
+    attrib = T(scalar_type{0});
+  } else if (va.divisor != 0) {
+    char* src = (char*)va.buf + va.stride * instance + va.offset;
+    assert(src + va.size <= va.buf + va.buf_size);
+    attrib = T(load_attrib_scalar<scalar_type>(va, src));
+  } else {
+    // Specialized for WR's primitive vertex order/winding.
+    if (!count) return;
+    assert(count >= 2 && count <= 4);
+    char* src = (char*)va.buf + va.stride * start + va.offset;
+    switch (count) {
+      case 2: {
+        // Lines must be indexed at offsets 0, 1.
+        // Line vertexes fill vertex shader SIMD lanes as 0, 1, 1, 0.
+        scalar_type lanes[2] = {
+            load_attrib_scalar<scalar_type>(va, src),
+            load_attrib_scalar<scalar_type>(va, src + va.stride)};
+        attrib = (T){lanes[0], lanes[1], lanes[1], lanes[0]};
+        break;
+      }
+      case 3: {
+        // Triangles must be indexed at offsets 0, 1, 2.
+        // Triangle vertexes fill vertex shader SIMD lanes as 0, 1, 2, 2.
+        scalar_type lanes[3] = {
+            load_attrib_scalar<scalar_type>(va, src),
+            load_attrib_scalar<scalar_type>(va, src + va.stride),
+            load_attrib_scalar<scalar_type>(va, src + va.stride * 2)};
+        attrib = (T){lanes[0], lanes[1], lanes[2], lanes[2]};
+        break;
+      }
+      default:
+        // Quads must be successive triangles indexed at offsets 0, 1, 2, 2,
+        // 1, 3. Quad vertexes fill vertex shader SIMD lanes as 0, 1, 3, 2, so
+        // that the points form a convex path that can be traversed by the
+        // rasterizer.
+        attrib = (T){load_attrib_scalar<scalar_type>(va, src),
+                     load_attrib_scalar<scalar_type>(va, src + va.stride),
+                     load_attrib_scalar<scalar_type>(va, src + va.stride * 3),
+                     load_attrib_scalar<scalar_type>(va, src + va.stride * 2)};
+        break;
+    }
+  }
+}
+
+template <typename T>
+void load_flat_attrib(T& attrib, VertexAttrib& va, uint32_t start, int instance,
+                      int count) {
+  typedef decltype(force_scalar(attrib)) scalar_type;
+  if (!va.enabled) {
+    attrib = T{0};
+    return;
+  }
+  char* src = nullptr;
+  if (va.divisor != 0) {
+    src = (char*)va.buf + va.stride * instance + va.offset;
+  } else {
+    if (!count) return;
+    src = (char*)va.buf + va.stride * start + va.offset;
+  }
+  assert(src + va.size <= va.buf + va.buf_size);
+  attrib = T(load_attrib_scalar<scalar_type>(va, src));
+}
+
+void setup_program(GLuint program) {
+  if (!program) {
+    vertex_shader = nullptr;
+    fragment_shader = nullptr;
+    return;
+  }
+  Program& p = ctx->programs[program];
+  assert(p.impl);
+  assert(p.vert_impl);
+  assert(p.frag_impl);
+  vertex_shader = p.vert_impl;
+  fragment_shader = p.frag_impl;
+}
+
+extern ProgramLoader load_shader(const char* name);
+
+extern "C" {
+
+void UseProgram(GLuint program) {
+  if (ctx->current_program && program != ctx->current_program) {
+    auto* p = ctx->programs.find(ctx->current_program);
+    if (p && p->deleted) {
+      ctx->programs.erase(ctx->current_program);
+    }
+  }
+  ctx->current_program = program;
+  setup_program(program);
+}
+
+void SetViewport(GLint x, GLint y, GLsizei width, GLsizei height) {
+  ctx->viewport = IntRect{x, y, x + width, y + height};
+}
+
+void Enable(GLenum cap) {
+  switch (cap) {
+    case GL_BLEND:
+      ctx->blend = true;
+      break;
+    case GL_DEPTH_TEST:
+      ctx->depthtest = true;
+      break;
+    case GL_SCISSOR_TEST:
+      ctx->scissortest = true;
+      break;
+  }
+}
+
+void Disable(GLenum cap) {
+  switch (cap) {
+    case GL_BLEND:
+      ctx->blend = false;
+      break;
+    case GL_DEPTH_TEST:
+      ctx->depthtest = false;
+      break;
+    case GL_SCISSOR_TEST:
+      ctx->scissortest = false;
+      break;
+  }
+}
+
+GLenum GetError() { return GL_NO_ERROR; }
+
+static const char* const extensions[] = {
+    "GL_ARB_blend_func_extended", "GL_ARB_copy_image",
+    "GL_ARB_draw_instanced",      "GL_ARB_explicit_attrib_location",
+    "GL_ARB_instanced_arrays",    "GL_ARB_invalidate_subdata",
+    "GL_ARB_texture_storage",     "GL_EXT_timer_query",
+    "GL_APPLE_rgb_422",
+};
+
+void GetIntegerv(GLenum pname, GLint* params) {
+  assert(params);
+  switch (pname) {
+    case GL_MAX_TEXTURE_UNITS:
+    case GL_MAX_TEXTURE_IMAGE_UNITS:
+      params[0] = MAX_TEXTURE_UNITS;
+      break;
+    case GL_MAX_TEXTURE_SIZE:
+      params[0] = 1 << 15;
+      break;
+    case GL_MAX_ARRAY_TEXTURE_LAYERS:
+      params[0] = 1 << 15;
+      break;
+    case GL_READ_FRAMEBUFFER_BINDING:
+      params[0] = ctx->read_framebuffer_binding;
+      break;
+    case GL_DRAW_FRAMEBUFFER_BINDING:
+      params[0] = ctx->draw_framebuffer_binding;
+      break;
+    case GL_PIXEL_PACK_BUFFER_BINDING:
+      params[0] = ctx->pixel_pack_buffer_binding;
+      break;
+    case GL_PIXEL_UNPACK_BUFFER_BINDING:
+      params[0] = ctx->pixel_unpack_buffer_binding;
+      break;
+    case GL_NUM_EXTENSIONS:
+      params[0] = sizeof(extensions) / sizeof(extensions[0]);
+      break;
+    case GL_MAJOR_VERSION:
+      params[0] = 3;
+      break;
+    case GL_MINOR_VERSION:
+      params[0] = 2;
+      break;
+    default:
+      debugf("unhandled glGetIntegerv parameter %x\n", pname);
+      assert(false);
+  }
+}
+
+void GetBooleanv(GLenum pname, GLboolean* params) {
+  assert(params);
+  switch (pname) {
+    case GL_DEPTH_WRITEMASK:
+      params[0] = ctx->depthmask;
+      break;
+    default:
+      debugf("unhandled glGetBooleanv parameter %x\n", pname);
+      assert(false);
+  }
+}
+
+const char* GetString(GLenum name) {
+  switch (name) {
+    case GL_VENDOR:
+      return "Mozilla Gfx";
+    case GL_RENDERER:
+      return "Software WebRender";
+    case GL_VERSION:
+      return "3.2";
+    default:
+      debugf("unhandled glGetString parameter %x\n", name);
+      assert(false);
+      return nullptr;
+  }
+}
+
+const char* GetStringi(GLenum name, GLuint index) {
+  switch (name) {
+    case GL_EXTENSIONS:
+      if (index >= sizeof(extensions) / sizeof(extensions[0])) {
+        return nullptr;
+      }
+      return extensions[index];
+    default:
+      debugf("unhandled glGetStringi parameter %x\n", name);
+      assert(false);
+      return nullptr;
+  }
+}
+
+GLenum remap_blendfunc(GLenum rgb, GLenum a) {
+  switch (a) {
+    case GL_SRC_ALPHA:
+      if (rgb == GL_SRC_COLOR) a = GL_SRC_COLOR;
+      break;
+    case GL_ONE_MINUS_SRC_ALPHA:
+      if (rgb == GL_ONE_MINUS_SRC_COLOR) a = GL_ONE_MINUS_SRC_COLOR;
+      break;
+    case GL_DST_ALPHA:
+      if (rgb == GL_DST_COLOR) a = GL_DST_COLOR;
+      break;
+    case GL_ONE_MINUS_DST_ALPHA:
+      if (rgb == GL_ONE_MINUS_DST_COLOR) a = GL_ONE_MINUS_DST_COLOR;
+      break;
+    case GL_CONSTANT_ALPHA:
+      if (rgb == GL_CONSTANT_COLOR) a = GL_CONSTANT_COLOR;
+      break;
+    case GL_ONE_MINUS_CONSTANT_ALPHA:
+      if (rgb == GL_ONE_MINUS_CONSTANT_COLOR) a = GL_ONE_MINUS_CONSTANT_COLOR;
+      break;
+    case GL_SRC_COLOR:
+      if (rgb == GL_SRC_ALPHA) a = GL_SRC_ALPHA;
+      break;
+    case GL_ONE_MINUS_SRC_COLOR:
+      if (rgb == GL_ONE_MINUS_SRC_ALPHA) a = GL_ONE_MINUS_SRC_ALPHA;
+      break;
+    case GL_DST_COLOR:
+      if (rgb == GL_DST_ALPHA) a = GL_DST_ALPHA;
+      break;
+    case GL_ONE_MINUS_DST_COLOR:
+      if (rgb == GL_ONE_MINUS_DST_ALPHA) a = GL_ONE_MINUS_DST_ALPHA;
+      break;
+    case GL_CONSTANT_COLOR:
+      if (rgb == GL_CONSTANT_ALPHA) a = GL_CONSTANT_ALPHA;
+      break;
+    case GL_ONE_MINUS_CONSTANT_COLOR:
+      if (rgb == GL_ONE_MINUS_CONSTANT_ALPHA) a = GL_ONE_MINUS_CONSTANT_ALPHA;
+      break;
+    case GL_SRC1_ALPHA:
+      if (rgb == GL_SRC1_COLOR) a = GL_SRC1_COLOR;
+      break;
+    case GL_ONE_MINUS_SRC1_ALPHA:
+      if (rgb == GL_ONE_MINUS_SRC1_COLOR) a = GL_ONE_MINUS_SRC1_COLOR;
+      break;
+    case GL_SRC1_COLOR:
+      if (rgb == GL_SRC1_ALPHA) a = GL_SRC1_ALPHA;
+      break;
+    case GL_ONE_MINUS_SRC1_COLOR:
+      if (rgb == GL_ONE_MINUS_SRC1_ALPHA) a = GL_ONE_MINUS_SRC1_ALPHA;
+      break;
+  }
+  return a;
+}
+
+void BlendFunc(GLenum srgb, GLenum drgb, GLenum sa, GLenum da) {
+  ctx->blendfunc_srgb = srgb;
+  ctx->blendfunc_drgb = drgb;
+  sa = remap_blendfunc(srgb, sa);
+  da = remap_blendfunc(drgb, da);
+  ctx->blendfunc_sa = sa;
+  ctx->blendfunc_da = da;
+
+#define HASH_BLEND_KEY(x, y, z, w) ((x << 4) | (y) | (z << 24) | (w << 20))
+  int hash = HASH_BLEND_KEY(srgb, drgb, 0, 0);
+  if (srgb != sa || drgb != da) hash |= HASH_BLEND_KEY(0, 0, sa, da);
+  switch (hash) {
+#define MAP_BLEND_KEY(...)                   \
+  case HASH_BLEND_KEY(__VA_ARGS__):          \
+    ctx->blend_key = BLEND_KEY(__VA_ARGS__); \
+    break;
+    FOR_EACH_BLEND_KEY(MAP_BLEND_KEY)
+    default:
+      debugf("blendfunc: %x, %x, separate: %x, %x\n", srgb, drgb, sa, da);
+      assert(false);
+      break;
+  }
+}
+
+void BlendColor(GLfloat r, GLfloat g, GLfloat b, GLfloat a) {
+  I32 c = round_pixel((Float){b, g, r, a});
+  ctx->blendcolor = CONVERT(c, U16).xyzwxyzw;
+}
+
+void BlendEquation(GLenum mode) {
+  assert(mode == GL_FUNC_ADD);
+  ctx->blend_equation = mode;
+}
+
+void DepthMask(GLboolean flag) { ctx->depthmask = flag; }
+
+void DepthFunc(GLenum func) {
+  switch (func) {
+    case GL_LESS:
+    case GL_LEQUAL:
+      break;
+    default:
+      assert(false);
+  }
+  ctx->depthfunc = func;
+}
+
+void SetScissor(GLint x, GLint y, GLsizei width, GLsizei height) {
+  ctx->scissor = IntRect{x, y, x + width, y + height};
+}
+
+void ClearColor(GLfloat r, GLfloat g, GLfloat b, GLfloat a) {
+  I32 c = round_pixel((Float){b, g, r, a});
+  ctx->clearcolor = bit_cast<uint32_t>(CONVERT(c, U8));
+}
+
+void ClearDepth(GLdouble depth) { ctx->cleardepth = depth; }
+
+void ActiveTexture(GLenum texture) {
+  assert(texture >= GL_TEXTURE0);
+  assert(texture < GL_TEXTURE0 + MAX_TEXTURE_UNITS);
+  ctx->active_texture_unit =
+      clamp(int(texture - GL_TEXTURE0), 0, int(MAX_TEXTURE_UNITS - 1));
+}
+
+void GenQueries(GLsizei n, GLuint* result) {
+  for (int i = 0; i < n; i++) {
+    Query q;
+    result[i] = ctx->queries.insert(q);
+  }
+}
+
+void DeleteQuery(GLuint n) {
+  if (n && ctx->queries.erase(n)) {
+    unlink(ctx->time_elapsed_query, n);
+    unlink(ctx->samples_passed_query, n);
+  }
+}
+
+void GenBuffers(int n, GLuint* result) {
+  for (int i = 0; i < n; i++) {
+    Buffer b;
+    result[i] = ctx->buffers.insert(b);
+  }
+}
+
+void DeleteBuffer(GLuint n) {
+  if (n && ctx->buffers.erase(n)) {
+    unlink(ctx->pixel_pack_buffer_binding, n);
+    unlink(ctx->pixel_unpack_buffer_binding, n);
+    unlink(ctx->array_buffer_binding, n);
+  }
+}
+
+void GenVertexArrays(int n, GLuint* result) {
+  for (int i = 0; i < n; i++) {
+    VertexArray v;
+    result[i] = ctx->vertex_arrays.insert(v);
+  }
+}
+
+void DeleteVertexArray(GLuint n) {
+  if (n && ctx->vertex_arrays.erase(n)) {
+    unlink(ctx->current_vertex_array, n);
+  }
+}
+
+GLuint CreateShader(GLenum type) {
+  Shader s;
+  s.type = type;
+  return ctx->shaders.insert(s);
+}
+
+void ShaderSourceByName(GLuint shader, char* name) {
+  Shader& s = ctx->shaders[shader];
+  s.loader = load_shader(name);
+  if (!s.loader) {
+    debugf("unknown shader %s\n", name);
+  }
+}
+
+void AttachShader(GLuint program, GLuint shader) {
+  Program& p = ctx->programs[program];
+  Shader& s = ctx->shaders[shader];
+  if (s.type == GL_VERTEX_SHADER) {
+    if (!p.impl && s.loader) p.impl = s.loader();
+  } else if (s.type == GL_FRAGMENT_SHADER) {
+    if (!p.impl && s.loader) p.impl = s.loader();
+  } else {
+    assert(0);
+  }
+}
+
+void DeleteShader(GLuint n) {
+  if (n) ctx->shaders.erase(n);
+}
+
+GLuint CreateProgram() {
+  Program p;
+  return ctx->programs.insert(p);
+}
+
+void DeleteProgram(GLuint n) {
+  if (!n) return;
+  if (ctx->current_program == n) {
+    if (auto* p = ctx->programs.find(n)) {
+      p->deleted = true;
+    }
+  } else {
+    ctx->programs.erase(n);
+  }
+}
+
+void LinkProgram(GLuint program) {
+  Program& p = ctx->programs[program];
+  assert(p.impl);
+  if (!p.impl) {
+    return;
+  }
+  assert(p.impl->interpolants_size() <= sizeof(Interpolants));
+  if (!p.vert_impl) p.vert_impl = p.impl->get_vertex_shader();
+  if (!p.frag_impl) p.frag_impl = p.impl->get_fragment_shader();
+}
+
+GLint GetLinkStatus(GLuint program) {
+  if (auto* p = ctx->programs.find(program)) {
+    return p->impl ? 1 : 0;
+  }
+  return 0;
+}
+
+void BindAttribLocation(GLuint program, GLuint index, char* name) {
+  Program& p = ctx->programs[program];
+  assert(p.impl);
+  if (!p.impl) {
+    return;
+  }
+  p.impl->bind_attrib(name, index);
+}
+
+GLint GetAttribLocation(GLuint program, char* name) {
+  Program& p = ctx->programs[program];
+  assert(p.impl);
+  if (!p.impl) {
+    return -1;
+  }
+  return p.impl->get_attrib(name);
+}
+
+GLint GetUniformLocation(GLuint program, char* name) {
+  Program& p = ctx->programs[program];
+  assert(p.impl);
+  if (!p.impl) {
+    return -1;
+  }
+  GLint loc = p.impl->get_uniform(name);
+  // debugf("location: %d\n", loc);
+  return loc;
+}
+
+static uint64_t get_time_value() {
+#ifdef __MACH__
+  return mach_absolute_time();
+#elif defined(_WIN32)
+  LARGE_INTEGER time;
+  static bool have_frequency = false;
+  static LARGE_INTEGER frequency;
+  if (!have_frequency) {
+    QueryPerformanceFrequency(&frequency);
+    have_frequency = true;
+  }
+  QueryPerformanceCounter(&time);
+  return time.QuadPart * 1000000000ULL / frequency.QuadPart;
+#else
+  return ({
+    struct timespec tp;
+    clock_gettime(CLOCK_MONOTONIC, &tp);
+    tp.tv_sec * 1000000000ULL + tp.tv_nsec;
+  });
+#endif
+}
+
+void BeginQuery(GLenum target, GLuint id) {
+  ctx->get_binding(target) = id;
+  Query& q = ctx->queries[id];
+  switch (target) {
+    case GL_SAMPLES_PASSED:
+      q.value = 0;
+      break;
+    case GL_TIME_ELAPSED:
+      q.value = get_time_value();
+      break;
+    default:
+      debugf("unknown query target %x for query %d\n", target, id);
+      assert(false);
+  }
+}
+
+void EndQuery(GLenum target) {
+  Query& q = ctx->queries[ctx->get_binding(target)];
+  switch (target) {
+    case GL_SAMPLES_PASSED:
+      break;
+    case GL_TIME_ELAPSED:
+      q.value = get_time_value() - q.value;
+      break;
+    default:
+      debugf("unknown query target %x\n", target);
+      assert(false);
+  }
+  ctx->get_binding(target) = 0;
+}
+
+void GetQueryObjectui64v(GLuint id, GLenum pname, GLuint64* params) {
+  Query& q = ctx->queries[id];
+  switch (pname) {
+    case GL_QUERY_RESULT:
+      assert(params);
+      params[0] = q.value;
+      break;
+    default:
+      assert(false);
+  }
+}
+
+void BindVertexArray(GLuint vertex_array) {
+  if (vertex_array != ctx->current_vertex_array) {
+    ctx->validate_vertex_array = true;
+  }
+  ctx->current_vertex_array = vertex_array;
+}
+
+void BindTexture(GLenum target, GLuint texture) {
+  ctx->get_binding(target) = texture;
+}
+
+void BindBuffer(GLenum target, GLuint buffer) {
+  ctx->get_binding(target) = buffer;
+}
+
+void BindFramebuffer(GLenum target, GLuint fb) {
+  if (target == GL_FRAMEBUFFER) {
+    ctx->read_framebuffer_binding = fb;
+    ctx->draw_framebuffer_binding = fb;
+  } else {
+    assert(target == GL_READ_FRAMEBUFFER || target == GL_DRAW_FRAMEBUFFER);
+    ctx->get_binding(target) = fb;
+  }
+}
+
+void BindRenderbuffer(GLenum target, GLuint rb) {
+  ctx->get_binding(target) = rb;
+}
+
+void PixelStorei(GLenum name, GLint param) {
+  if (name == GL_UNPACK_ALIGNMENT) {
+    assert(param == 1);
+  } else if (name == GL_UNPACK_ROW_LENGTH) {
+    ctx->unpack_row_length = param;
+  }
+}
+
+static GLenum remap_internal_format(GLenum format) {
+  switch (format) {
+    case GL_DEPTH_COMPONENT:
+      return GL_DEPTH_COMPONENT16;
+    case GL_RGBA:
+      return GL_RGBA8;
+    case GL_RED:
+      return GL_R8;
+    case GL_RG:
+      return GL_RG8;
+    case GL_RGB_422_APPLE:
+      return GL_RGB_RAW_422_APPLE;
+    default:
+      return format;
+  }
+}
+
+void TexStorage3D(GLenum target, GLint levels, GLenum internal_format,
+                  GLsizei width, GLsizei height, GLsizei depth) {
+  assert(levels == 1);
+  Texture& t = ctx->textures[ctx->get_binding(target)];
+  internal_format = remap_internal_format(internal_format);
+  bool changed = false;
+  if (t.width != width || t.height != height || t.depth != depth ||
+      t.internal_format != internal_format) {
+    changed = true;
+    t.internal_format = internal_format;
+    t.width = width;
+    t.height = height;
+    t.depth = depth;
+  }
+  t.disable_delayed_clear();
+  t.allocate(changed);
+}
+
+}  // extern "C"
+
+static bool format_requires_conversion(GLenum external_format,
+                                       GLenum internal_format) {
+  switch (external_format) {
+    case GL_RGBA:
+      return internal_format == GL_RGBA8;
+    default:
+      return false;
+  }
+}
+
+static inline void copy_bgra8_to_rgba8(uint32_t* dest, const uint32_t* src,
+                                       int width) {
+  for (; width >= 4; width -= 4, dest += 4, src += 4) {
+    U32 p = unaligned_load<U32>(src);
+    U32 rb = p & 0x00FF00FF;
+    unaligned_store(dest, (p & 0xFF00FF00) | (rb << 16) | (rb >> 16));
+  }
+  for (; width > 0; width--, dest++, src++) {
+    uint32_t p = *src;
+    uint32_t rb = p & 0x00FF00FF;
+    *dest = (p & 0xFF00FF00) | (rb << 16) | (rb >> 16);
+  }
+}
+
+static void convert_copy(GLenum external_format, GLenum internal_format,
+                         uint8_t* dst_buf, size_t dst_stride,
+                         const uint8_t* src_buf, size_t src_stride,
+                         size_t width, size_t height) {
+  switch (external_format) {
+    case GL_RGBA:
+      if (internal_format == GL_RGBA8) {
+        for (; height; height--) {
+          copy_bgra8_to_rgba8((uint32_t*)dst_buf, (const uint32_t*)src_buf,
+                              width);
+          dst_buf += dst_stride;
+          src_buf += src_stride;
+        }
+        return;
+      }
+      break;
+    default:
+      break;
+  }
+  size_t row_bytes = width * bytes_for_internal_format(internal_format);
+  for (; height; height--) {
+    memcpy(dst_buf, src_buf, row_bytes);
+    dst_buf += dst_stride;
+    src_buf += src_stride;
+  }
+}
+
+static void set_tex_storage(Texture& t, GLenum external_format, GLsizei width,
+                            GLsizei height, void* buf = nullptr,
+                            GLsizei stride = 0, GLsizei min_width = 0,
+                            GLsizei min_height = 0) {
+  GLenum internal_format = remap_internal_format(external_format);
+  bool changed = false;
+  if (t.width != width || t.height != height || t.depth != 0 ||
+      t.internal_format != internal_format) {
+    changed = true;
+    t.internal_format = internal_format;
+    t.width = width;
+    t.height = height;
+    t.depth = 0;
+  }
+  // If we are changed from an internally managed buffer to an externally
+  // supplied one or vice versa, ensure that we clean up old buffer state.
+  // However, if we have to convert the data from a non-native format, then
+  // always treat it as internally managed since we will need to copy to an
+  // internally managed native format buffer.
+  bool should_free = buf == nullptr || format_requires_conversion(
+                                           external_format, internal_format);
+  if (t.should_free() != should_free) {
+    changed = true;
+    t.cleanup();
+    t.set_should_free(should_free);
+  }
+  // If now an external buffer, explicitly set it...
+  if (!should_free) {
+    t.set_buffer(buf, stride);
+  }
+  t.disable_delayed_clear();
+  t.allocate(changed, min_width, min_height);
+  // If we have a buffer that needs format conversion, then do that now.
+  if (buf && should_free) {
+    convert_copy(external_format, internal_format, (uint8_t*)t.buf, t.stride(),
+                 (const uint8_t*)buf, stride, width, height);
+  }
+}
+
+extern "C" {
+
+void TexStorage2D(GLenum target, GLint levels, GLenum internal_format,
+                  GLsizei width, GLsizei height) {
+  assert(levels == 1);
+  Texture& t = ctx->textures[ctx->get_binding(target)];
+  set_tex_storage(t, internal_format, width, height);
+}
+
+GLenum internal_format_for_data(GLenum format, GLenum ty) {
+  if (format == GL_RED && ty == GL_UNSIGNED_BYTE) {
+    return GL_R8;
+  } else if ((format == GL_RGBA || format == GL_BGRA) &&
+             (ty == GL_UNSIGNED_BYTE || ty == GL_UNSIGNED_INT_8_8_8_8_REV)) {
+    return GL_RGBA8;
+  } else if (format == GL_RGBA && ty == GL_FLOAT) {
+    return GL_RGBA32F;
+  } else if (format == GL_RGBA_INTEGER && ty == GL_INT) {
+    return GL_RGBA32I;
+  } else if (format == GL_RG && ty == GL_UNSIGNED_BYTE) {
+    return GL_RG8;
+  } else if (format == GL_RGB_422_APPLE &&
+             ty == GL_UNSIGNED_SHORT_8_8_REV_APPLE) {
+    return GL_RGB_RAW_422_APPLE;
+  } else if (format == GL_RED && ty == GL_UNSIGNED_SHORT) {
+    return GL_R16;
+  } else {
+    debugf("unknown internal format for format %x, type %x\n", format, ty);
+    assert(false);
+    return 0;
+  }
+}
+
+static Buffer* get_pixel_pack_buffer() {
+  return ctx->pixel_pack_buffer_binding
+             ? &ctx->buffers[ctx->pixel_pack_buffer_binding]
+             : nullptr;
+}
+
+static void* get_pixel_pack_buffer_data(void* data) {
+  if (Buffer* b = get_pixel_pack_buffer()) {
+    return b->buf ? b->buf + (size_t)data : nullptr;
+  }
+  return data;
+}
+
+static Buffer* get_pixel_unpack_buffer() {
+  return ctx->pixel_unpack_buffer_binding
+             ? &ctx->buffers[ctx->pixel_unpack_buffer_binding]
+             : nullptr;
+}
+
+static void* get_pixel_unpack_buffer_data(void* data) {
+  if (Buffer* b = get_pixel_unpack_buffer()) {
+    return b->buf ? b->buf + (size_t)data : nullptr;
+  }
+  return data;
+}
+
+void TexSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset,
+                   GLsizei width, GLsizei height, GLenum format, GLenum ty,
+                   void* data) {
+  if (level != 0) {
+    assert(false);
+    return;
+  }
+  data = get_pixel_unpack_buffer_data(data);
+  if (!data) return;
+  Texture& t = ctx->textures[ctx->get_binding(target)];
+  IntRect skip = {xoffset, yoffset, xoffset + width, yoffset + height};
+  prepare_texture(t, &skip);
+  assert(xoffset + width <= t.width);
+  assert(yoffset + height <= t.height);
+  assert(ctx->unpack_row_length == 0 || ctx->unpack_row_length >= width);
+  GLsizei row_length =
+      ctx->unpack_row_length != 0 ? ctx->unpack_row_length : width;
+  assert(t.internal_format == internal_format_for_data(format, ty));
+  int src_bpp = format_requires_conversion(format, t.internal_format)
+                    ? bytes_for_internal_format(format)
+                    : t.bpp();
+  if (!src_bpp || !t.buf) return;
+  convert_copy(format, t.internal_format,
+               (uint8_t*)t.sample_ptr(xoffset, yoffset), t.stride(),
+               (const uint8_t*)data, row_length * src_bpp, width, height);
+}
+
+void TexImage2D(GLenum target, GLint level, GLint internal_format,
+                GLsizei width, GLsizei height, GLint border, GLenum format,
+                GLenum ty, void* data) {
+  if (level != 0) {
+    assert(false);
+    return;
+  }
+  assert(border == 0);
+  TexStorage2D(target, 1, internal_format, width, height);
+  TexSubImage2D(target, 0, 0, 0, width, height, format, ty, data);
+}
+
+void TexSubImage3D(GLenum target, GLint level, GLint xoffset, GLint yoffset,
+                   GLint zoffset, GLsizei width, GLsizei height, GLsizei depth,
+                   GLenum format, GLenum ty, void* data) {
+  if (level != 0) {
+    assert(false);
+    return;
+  }
+  data = get_pixel_unpack_buffer_data(data);
+  if (!data) return;
+  Texture& t = ctx->textures[ctx->get_binding(target)];
+  prepare_texture(t);
+  assert(ctx->unpack_row_length == 0 || ctx->unpack_row_length >= width);
+  GLsizei row_length =
+      ctx->unpack_row_length != 0 ? ctx->unpack_row_length : width;
+  assert(t.internal_format == internal_format_for_data(format, ty));
+  int src_bpp = format_requires_conversion(format, t.internal_format)
+                    ? bytes_for_internal_format(format)
+                    : t.bpp();
+  if (!src_bpp || !t.buf) return;
+  const uint8_t* src = (const uint8_t*)data;
+  assert(xoffset + width <= t.width);
+  assert(yoffset + height <= t.height);
+  assert(zoffset + depth <= t.depth);
+  size_t dest_stride = t.stride();
+  size_t src_stride = row_length * src_bpp;
+  for (int z = 0; z < depth; z++) {
+    convert_copy(format, t.internal_format,
+                 (uint8_t*)t.sample_ptr(xoffset, yoffset, zoffset + z),
+                 dest_stride, src, src_stride, width, height);
+    src += src_stride * height;
+  }
+}
+
+void TexImage3D(GLenum target, GLint level, GLint internal_format,
+                GLsizei width, GLsizei height, GLsizei depth, GLint border,
+                GLenum format, GLenum ty, void* data) {
+  if (level != 0) {
+    assert(false);
+    return;
+  }
+  assert(border == 0);
+  TexStorage3D(target, 1, internal_format, width, height, depth);
+  TexSubImage3D(target, 0, 0, 0, 0, width, height, depth, format, ty, data);
+}
+
+void GenerateMipmap(UNUSED GLenum target) {
+  // TODO: support mipmaps
+}
+
+void SetTextureParameter(GLuint texid, GLenum pname, GLint param) {
+  Texture& t = ctx->textures[texid];
+  switch (pname) {
+    case GL_TEXTURE_WRAP_S:
+      assert(param == GL_CLAMP_TO_EDGE);
+      break;
+    case GL_TEXTURE_WRAP_T:
+      assert(param == GL_CLAMP_TO_EDGE);
+      break;
+    case GL_TEXTURE_MIN_FILTER:
+      t.min_filter = param;
+      break;
+    case GL_TEXTURE_MAG_FILTER:
+      t.mag_filter = param;
+      break;
+    default:
+      break;
+  }
+}
+
+void TexParameteri(GLenum target, GLenum pname, GLint param) {
+  SetTextureParameter(ctx->get_binding(target), pname, param);
+}
+
+void GenTextures(int n, GLuint* result) {
+  for (int i = 0; i < n; i++) {
+    Texture t;
+    result[i] = ctx->textures.insert(t);
+  }
+}
+
+void DeleteTexture(GLuint n) {
+  if (n && ctx->textures.erase(n)) {
+    for (size_t i = 0; i < MAX_TEXTURE_UNITS; i++) {
+      ctx->texture_units[i].unlink(n);
+    }
+  }
+}
+
+void GenRenderbuffers(int n, GLuint* result) {
+  for (int i = 0; i < n; i++) {
+    Renderbuffer r;
+    result[i] = ctx->renderbuffers.insert(r);
+  }
+}
+
+void Renderbuffer::on_erase() {
+  for (auto* fb : ctx->framebuffers) {
+    if (fb) {
+      if (unlink(fb->color_attachment, texture)) {
+        fb->layer = 0;
+      }
+      unlink(fb->depth_attachment, texture);
+    }
+  }
+  DeleteTexture(texture);
+}
+
+void DeleteRenderbuffer(GLuint n) {
+  if (n && ctx->renderbuffers.erase(n)) {
+    unlink(ctx->renderbuffer_binding, n);
+  }
+}
+
+void GenFramebuffers(int n, GLuint* result) {
+  for (int i = 0; i < n; i++) {
+    Framebuffer f;
+    result[i] = ctx->framebuffers.insert(f);
+  }
+}
+
+void DeleteFramebuffer(GLuint n) {
+  if (n && ctx->framebuffers.erase(n)) {
+    unlink(ctx->read_framebuffer_binding, n);
+    unlink(ctx->draw_framebuffer_binding, n);
+  }
+}
+
+void RenderbufferStorage(GLenum target, GLenum internal_format, GLsizei width,
+                         GLsizei height) {
+  // Just refer a renderbuffer to a texture to simplify things for now...
+  Renderbuffer& r = ctx->renderbuffers[ctx->get_binding(target)];
+  if (!r.texture) {
+    GenTextures(1, &r.texture);
+  }
+  switch (internal_format) {
+    case GL_DEPTH_COMPONENT:
+    case GL_DEPTH_COMPONENT24:
+    case GL_DEPTH_COMPONENT32:
+      // Force depth format to 16 bits...
+      internal_format = GL_DEPTH_COMPONENT16;
+      break;
+  }
+  set_tex_storage(ctx->textures[r.texture], internal_format, width, height);
+}
+
+void VertexAttribPointer(GLuint index, GLint size, GLenum type, bool normalized,
+                         GLsizei stride, GLuint offset) {
+  // debugf("cva: %d\n", ctx->current_vertex_array);
+  VertexArray& v = ctx->vertex_arrays[ctx->current_vertex_array];
+  if (index >= NULL_ATTRIB) {
+    assert(0);
+    return;
+  }
+  VertexAttrib& va = v.attribs[index];
+  va.size = size * bytes_per_type(type);
+  va.type = type;
+  va.normalized = normalized;
+  va.stride = stride;
+  va.offset = offset;
+  // Buffer &vertex_buf = ctx->buffers[ctx->array_buffer_binding];
+  va.vertex_buffer = ctx->array_buffer_binding;
+  va.vertex_array = ctx->current_vertex_array;
+  ctx->validate_vertex_array = true;
+}
+
+void VertexAttribIPointer(GLuint index, GLint size, GLenum type, GLsizei stride,
+                          GLuint offset) {
+  // debugf("cva: %d\n", ctx->current_vertex_array);
+  VertexArray& v = ctx->vertex_arrays[ctx->current_vertex_array];
+  if (index >= NULL_ATTRIB) {
+    assert(0);
+    return;
+  }
+  VertexAttrib& va = v.attribs[index];
+  va.size = size * bytes_per_type(type);
+  va.type = type;
+  va.normalized = false;
+  va.stride = stride;
+  va.offset = offset;
+  // Buffer &vertex_buf = ctx->buffers[ctx->array_buffer_binding];
+  va.vertex_buffer = ctx->array_buffer_binding;
+  va.vertex_array = ctx->current_vertex_array;
+  ctx->validate_vertex_array = true;
+}
+
+void EnableVertexAttribArray(GLuint index) {
+  VertexArray& v = ctx->vertex_arrays[ctx->current_vertex_array];
+  if (index >= NULL_ATTRIB) {
+    assert(0);
+    return;
+  }
+  VertexAttrib& va = v.attribs[index];
+  if (!va.enabled) {
+    ctx->validate_vertex_array = true;
+  }
+  va.enabled = true;
+  v.max_attrib = max(v.max_attrib, (int)index);
+}
+
+void DisableVertexAttribArray(GLuint index) {
+  VertexArray& v = ctx->vertex_arrays[ctx->current_vertex_array];
+  if (index >= NULL_ATTRIB) {
+    assert(0);
+    return;
+  }
+  VertexAttrib& va = v.attribs[index];
+  if (va.enabled) {
+    ctx->validate_vertex_array = true;
+  }
+  va.enabled = false;
+}
+
+void VertexAttribDivisor(GLuint index, GLuint divisor) {
+  VertexArray& v = ctx->vertex_arrays[ctx->current_vertex_array];
+  // Only support divisor being 0 (per-vertex) or 1 (per-instance).
+  if (index >= NULL_ATTRIB || divisor > 1) {
+    assert(0);
+    return;
+  }
+  VertexAttrib& va = v.attribs[index];
+  va.divisor = divisor;
+}
+
+void BufferData(GLenum target, GLsizeiptr size, void* data,
+                UNUSED GLenum usage) {
+  Buffer& b = ctx->buffers[ctx->get_binding(target)];
+  if (b.allocate(size)) {
+    ctx->validate_vertex_array = true;
+  }
+  if (data && b.buf && size <= b.size) {
+    memcpy(b.buf, data, size);
+  }
+}
+
+void BufferSubData(GLenum target, GLintptr offset, GLsizeiptr size,
+                   void* data) {
+  Buffer& b = ctx->buffers[ctx->get_binding(target)];
+  assert(offset + size <= b.size);
+  if (data && b.buf && offset + size <= b.size) {
+    memcpy(&b.buf[offset], data, size);
+  }
+}
+
+void* MapBuffer(GLenum target, UNUSED GLbitfield access) {
+  Buffer& b = ctx->buffers[ctx->get_binding(target)];
+  return b.buf;
+}
+
+void* MapBufferRange(GLenum target, GLintptr offset, GLsizeiptr length,
+                     UNUSED GLbitfield access) {
+  Buffer& b = ctx->buffers[ctx->get_binding(target)];
+  if (b.buf && offset >= 0 && length > 0 && offset + length <= b.size) {
+    return b.buf + offset;
+  }
+  return nullptr;
+}
+
+GLboolean UnmapBuffer(GLenum target) {
+  Buffer& b = ctx->buffers[ctx->get_binding(target)];
+  return b.buf != nullptr;
+}
+
+void Uniform1i(GLint location, GLint V0) {
+  // debugf("tex: %d\n", (int)ctx->textures.size);
+  if (vertex_shader) {
+    vertex_shader->set_uniform_1i(location, V0);
+  }
+}
+void Uniform4fv(GLint location, GLsizei count, const GLfloat* v) {
+  assert(count == 1);
+  if (vertex_shader) {
+    vertex_shader->set_uniform_4fv(location, v);
+  }
+}
+void UniformMatrix4fv(GLint location, GLsizei count, GLboolean transpose,
+                      const GLfloat* value) {
+  assert(count == 1);
+  assert(!transpose);
+  if (vertex_shader) {
+    vertex_shader->set_uniform_matrix4fv(location, value);
+  }
+}
+
+void FramebufferTexture2D(GLenum target, GLenum attachment, GLenum textarget,
+                          GLuint texture, GLint level) {
+  assert(target == GL_READ_FRAMEBUFFER || target == GL_DRAW_FRAMEBUFFER);
+  assert(textarget == GL_TEXTURE_2D || textarget == GL_TEXTURE_RECTANGLE);
+  assert(level == 0);
+  Framebuffer& fb = ctx->framebuffers[ctx->get_binding(target)];
+  if (attachment == GL_COLOR_ATTACHMENT0) {
+    fb.color_attachment = texture;
+    fb.layer = 0;
+  } else if (attachment == GL_DEPTH_ATTACHMENT) {
+    fb.depth_attachment = texture;
+  } else {
+    assert(0);
+  }
+}
+
+void FramebufferTextureLayer(GLenum target, GLenum attachment, GLuint texture,
+                             GLint level, GLint layer) {
+  assert(target == GL_READ_FRAMEBUFFER || target == GL_DRAW_FRAMEBUFFER);
+  assert(level == 0);
+  Framebuffer& fb = ctx->framebuffers[ctx->get_binding(target)];
+  if (attachment == GL_COLOR_ATTACHMENT0) {
+    fb.color_attachment = texture;
+    fb.layer = layer;
+  } else if (attachment == GL_DEPTH_ATTACHMENT) {
+    assert(layer == 0);
+    fb.depth_attachment = texture;
+  } else {
+    assert(0);
+  }
+}
+
+void FramebufferRenderbuffer(GLenum target, GLenum attachment,
+                             GLenum renderbuffertarget, GLuint renderbuffer) {
+  assert(target == GL_READ_FRAMEBUFFER || target == GL_DRAW_FRAMEBUFFER);
+  assert(renderbuffertarget == GL_RENDERBUFFER);
+  Framebuffer& fb = ctx->framebuffers[ctx->get_binding(target)];
+  Renderbuffer& rb = ctx->renderbuffers[renderbuffer];
+  if (attachment == GL_COLOR_ATTACHMENT0) {
+    fb.color_attachment = rb.texture;
+    fb.layer = 0;
+  } else if (attachment == GL_DEPTH_ATTACHMENT) {
+    fb.depth_attachment = rb.texture;
+  } else {
+    assert(0);
+  }
+}
+
+}  // extern "C"
+
+static inline Framebuffer* get_framebuffer(GLenum target) {
+  if (target == GL_FRAMEBUFFER) {
+    target = GL_DRAW_FRAMEBUFFER;
+  }
+  return ctx->framebuffers.find(ctx->get_binding(target));
+}
+
+template <typename T>
+static inline void fill_n(T* dst, size_t n, T val) {
+  for (T* end = &dst[n]; dst < end; dst++) *dst = val;
+}
+
+#if USE_SSE2
+template <>
+inline void fill_n<uint32_t>(uint32_t* dst, size_t n, uint32_t val) {
+  __asm__ __volatile__("rep stosl\n"
+                       : "+D"(dst), "+c"(n)
+                       : "a"(val)
+                       : "memory", "cc");
+}
+#endif
+
+static inline uint32_t clear_chunk(uint8_t value) {
+  return uint32_t(value) * 0x01010101U;
+}
+
+static inline uint32_t clear_chunk(uint16_t value) {
+  return uint32_t(value) | (uint32_t(value) << 16);
+}
+
+static inline uint32_t clear_chunk(uint32_t value) { return value; }
+
+template <typename T>
+static inline void clear_row(T* buf, size_t len, T value, uint32_t chunk) {
+  const size_t N = sizeof(uint32_t) / sizeof(T);
+  // fill any leading unaligned values
+  if (N > 1) {
+    size_t align = (-(intptr_t)buf & (sizeof(uint32_t) - 1)) / sizeof(T);
+    if (align <= len) {
+      fill_n(buf, align, value);
+      len -= align;
+      buf += align;
+    }
+  }
+  // fill as many aligned chunks as possible
+  fill_n((uint32_t*)buf, len / N, chunk);
+  // fill any remaining values
+  if (N > 1) {
+    fill_n(buf + (len & ~(N - 1)), len & (N - 1), value);
+  }
+}
+
+template <typename T>
+static void clear_buffer(Texture& t, T value, int layer, IntRect bb,
+                         int skip_start = 0, int skip_end = 0) {
+  if (!t.buf) return;
+  skip_start = max(skip_start, bb.x0);
+  skip_end = max(skip_end, skip_start);
+  assert(sizeof(T) == t.bpp());
+  size_t stride = t.stride();
+  // When clearing multiple full-width rows, collapse them into a single
+  // large "row" to avoid redundant setup from clearing each row individually.
+  if (bb.width() == t.width && bb.height() > 1 && skip_start >= skip_end) {
+    bb.x1 += (stride / sizeof(T)) * (bb.height() - 1);
+    bb.y1 = bb.y0 + 1;
+  }
+  T* buf = (T*)t.sample_ptr(bb.x0, bb.y0, layer);
+  uint32_t chunk = clear_chunk(value);
+  for (int rows = bb.height(); rows > 0; rows--) {
+    if (bb.x0 < skip_start) {
+      clear_row(buf, skip_start - bb.x0, value, chunk);
+    }
+    if (skip_end < bb.x1) {
+      clear_row(buf + (skip_end - bb.x0), bb.x1 - skip_end, value, chunk);
+    }
+    buf += stride / sizeof(T);
+  }
+}
+
+template <typename T>
+static inline void clear_buffer(Texture& t, T value, int layer = 0) {
+  IntRect bb = ctx->apply_scissor(t);
+  if (bb.width() > 0) {
+    clear_buffer<T>(t, value, layer, bb);
+  }
+}
+
+template <typename T>
+static inline void force_clear_row(Texture& t, int y, int skip_start = 0,
+                                   int skip_end = 0) {
+  assert(t.buf != nullptr);
+  assert(sizeof(T) == t.bpp());
+  assert(skip_start <= skip_end);
+  T* buf = (T*)t.sample_ptr(0, y);
+  uint32_t chunk = clear_chunk((T)t.clear_val);
+  if (skip_start > 0) {
+    clear_row<T>(buf, skip_start, t.clear_val, chunk);
+  }
+  if (skip_end < t.width) {
+    clear_row<T>(buf + skip_end, t.width - skip_end, t.clear_val, chunk);
+  }
+}
+
+template <typename T>
+static void force_clear(Texture& t, const IntRect* skip = nullptr) {
+  if (!t.delay_clear || !t.cleared_rows) {
+    return;
+  }
+  int y0 = 0;
+  int y1 = t.height;
+  int skip_start = 0;
+  int skip_end = 0;
+  if (skip) {
+    y0 = clamp(skip->y0, 0, t.height);
+    y1 = clamp(skip->y1, y0, t.height);
+    skip_start = clamp(skip->x0, 0, t.width);
+    skip_end = clamp(skip->x1, skip_start, t.width);
+    if (skip_start <= 0 && skip_end >= t.width && y0 <= 0 && y1 >= t.height) {
+      t.disable_delayed_clear();
+      return;
+    }
+  }
+  int num_masks = (y1 + 31) / 32;
+  uint32_t* rows = t.cleared_rows;
+  for (int i = y0 / 32; i < num_masks; i++) {
+    uint32_t mask = rows[i];
+    if (mask != ~0U) {
+      rows[i] = ~0U;
+      int start = i * 32;
+      while (mask) {
+        int count = __builtin_ctz(mask);
+        if (count > 0) {
+          clear_buffer<T>(t, t.clear_val, 0,
+                          IntRect{0, start, t.width, start + count}, skip_start,
+                          skip_end);
+          t.delay_clear -= count;
+          start += count;
+          mask >>= count;
+        }
+        count = __builtin_ctz(mask + 1);
+        start += count;
+        mask >>= count;
+      }
+      int count = (i + 1) * 32 - start;
+      if (count > 0) {
+        clear_buffer<T>(t, t.clear_val, 0,
+                        IntRect{0, start, t.width, start + count}, skip_start,
+                        skip_end);
+        t.delay_clear -= count;
+      }
+    }
+  }
+  if (t.delay_clear <= 0) t.disable_delayed_clear();
+}
+
+static void prepare_texture(Texture& t, const IntRect* skip) {
+  if (t.delay_clear) {
+    switch (t.internal_format) {
+      case GL_RGBA8:
+        force_clear<uint32_t>(t, skip);
+        break;
+      case GL_R8:
+        force_clear<uint8_t>(t, skip);
+        break;
+      case GL_RG8:
+        force_clear<uint16_t>(t, skip);
+        break;
+      default:
+        assert(false);
+        break;
+    }
+  }
+}
+
+static inline bool clear_requires_scissor(Texture& t) {
+  return ctx->scissortest && !ctx->scissor.contains(t.offset_bounds());
+}
+
+// Setup a clear on a texture. This may either force an immediate clear or
+// potentially punt to a delayed clear, if applicable.
+template <typename T>
+static void request_clear(Texture& t, int layer, T value) {
+  // If the clear would require a scissor, force clear anything outside
+  // the scissor, and then immediately clear anything inside the scissor.
+  if (clear_requires_scissor(t)) {
+    IntRect skip = ctx->scissor - t.offset;
+    force_clear<T>(t, &skip);
+    clear_buffer<T>(t, value, layer);
+  } else if (t.depth > 1) {
+    // Delayed clear is not supported on texture arrays.
+    t.disable_delayed_clear();
+    clear_buffer<T>(t, value, layer);
+  } else {
+    // Do delayed clear for 2D texture without scissor.
+    t.enable_delayed_clear(value);
+  }
+}
+
+// Initialize a depth texture by setting the first run in each row to encompass
+// the entire row.
+void Texture::init_depth_runs(uint16_t depth) {
+  if (!buf) return;
+  DepthRun* runs = (DepthRun*)buf;
+  for (int y = 0; y < height; y++) {
+    runs[0] = DepthRun(depth, width);
+    runs += stride() / sizeof(DepthRun);
+  }
+  set_cleared(true);
+}
+
+// Fill a portion of the run array with flattened depth samples.
+static ALWAYS_INLINE void fill_depth_run(DepthRun* dst, size_t n,
+                                         uint16_t depth) {
+  fill_n((uint32_t*)dst, n, uint32_t(depth));
+}
+
+// Fills a scissored region of a depth texture with a given depth.
+void Texture::fill_depth_runs(uint16_t depth) {
+  if (!buf) return;
+  assert(cleared());
+  IntRect bb = ctx->apply_scissor(*this);
+  DepthRun* runs = (DepthRun*)sample_ptr(0, bb.y0);
+  for (int rows = bb.height(); rows > 0; rows--) {
+    if (bb.width() >= width) {
+      // If the scissor region encompasses the entire row, reset the row to a
+      // single run encompassing the entire row.
+      runs[0] = DepthRun(depth, width);
+    } else if (runs->is_flat()) {
+      // If the row is flattened, just directly fill the portion of the row.
+      fill_depth_run(&runs[bb.x0], bb.width(), depth);
+    } else {
+      // Otherwise, if we are still using runs, then set up a cursor to fill
+      // it with depth runs.
+      DepthCursor(runs, width, bb.x0, bb.width()).fill(depth);
+    }
+    runs += stride() / sizeof(DepthRun);
+  }
+}
+
+extern "C" {
+
+void InitDefaultFramebuffer(int x, int y, int width, int height, int stride,
+                            void* buf) {
+  Framebuffer& fb = ctx->framebuffers[0];
+  if (!fb.color_attachment) {
+    GenTextures(1, &fb.color_attachment);
+    fb.layer = 0;
+  }
+  // If the dimensions or buffer properties changed, we need to reallocate
+  // the underlying storage for the color buffer texture.
+  Texture& colortex = ctx->textures[fb.color_attachment];
+  set_tex_storage(colortex, GL_RGBA8, width, height, buf, stride);
+  colortex.offset = IntPoint(x, y);
+  if (!fb.depth_attachment) {
+    GenTextures(1, &fb.depth_attachment);
+  }
+  // Ensure dimensions of the depth buffer match the color buffer.
+  Texture& depthtex = ctx->textures[fb.depth_attachment];
+  set_tex_storage(depthtex, GL_DEPTH_COMPONENT16, width, height);
+  depthtex.offset = IntPoint(x, y);
+}
+
+void* GetColorBuffer(GLuint fbo, GLboolean flush, int32_t* width,
+                     int32_t* height, int32_t* stride) {
+  Framebuffer* fb = ctx->framebuffers.find(fbo);
+  if (!fb || !fb->color_attachment) {
+    return nullptr;
+  }
+  Texture& colortex = ctx->textures[fb->color_attachment];
+  if (flush) {
+    prepare_texture(colortex);
+  }
+  assert(colortex.offset == IntPoint(0, 0));
+  *width = colortex.width;
+  *height = colortex.height;
+  *stride = colortex.stride();
+  return colortex.buf ? colortex.sample_ptr(0, 0, fb->layer) : nullptr;
+}
+
+void SetTextureBuffer(GLuint texid, GLenum internal_format, GLsizei width,
+                      GLsizei height, GLsizei stride, void* buf,
+                      GLsizei min_width, GLsizei min_height) {
+  Texture& t = ctx->textures[texid];
+  set_tex_storage(t, internal_format, width, height, buf, stride, min_width,
+                  min_height);
+}
+
+GLenum CheckFramebufferStatus(GLenum target) {
+  Framebuffer* fb = get_framebuffer(target);
+  if (!fb || !fb->color_attachment) {
+    return GL_FRAMEBUFFER_UNSUPPORTED;
+  }
+  return GL_FRAMEBUFFER_COMPLETE;
+}
+
+void Clear(GLbitfield mask) {
+  Framebuffer& fb = *get_framebuffer(GL_DRAW_FRAMEBUFFER);
+  if ((mask & GL_COLOR_BUFFER_BIT) && fb.color_attachment) {
+    Texture& t = ctx->textures[fb.color_attachment];
+    assert(!t.locked);
+    if (t.internal_format == GL_RGBA8) {
+      uint32_t color = ctx->clearcolor;
+      request_clear<uint32_t>(t, fb.layer, color);
+    } else if (t.internal_format == GL_R8) {
+      uint8_t color = uint8_t((ctx->clearcolor >> 16) & 0xFF);
+      request_clear<uint8_t>(t, fb.layer, color);
+    } else if (t.internal_format == GL_RG8) {
+      uint16_t color = uint16_t((ctx->clearcolor & 0xFF00) |
+                                ((ctx->clearcolor >> 16) & 0xFF));
+      request_clear<uint16_t>(t, fb.layer, color);
+    } else {
+      assert(false);
+    }
+  }
+  if ((mask & GL_DEPTH_BUFFER_BIT) && fb.depth_attachment) {
+    Texture& t = ctx->textures[fb.depth_attachment];
+    assert(t.internal_format == GL_DEPTH_COMPONENT16);
+    uint16_t depth = uint16_t(0xFFFF * ctx->cleardepth);
+    if (t.cleared() && clear_requires_scissor(t)) {
+      // If we need to scissor the clear and the depth buffer was already
+      // initialized, then just fill runs for that scissor area.
+      t.fill_depth_runs(depth);
+    } else {
+      // Otherwise, the buffer is either uninitialized or the clear would
+      // encompass the entire buffer. If uninitialized, we can safely fill
+      // the entire buffer with any value and thus ignore any scissoring.
+      t.init_depth_runs(depth);
+    }
+  }
+}
+
+void InvalidateFramebuffer(GLenum target, GLsizei num_attachments,
+                           const GLenum* attachments) {
+  Framebuffer* fb = get_framebuffer(target);
+  if (!fb || num_attachments <= 0 || !attachments) {
+    return;
+  }
+  for (GLsizei i = 0; i < num_attachments; i++) {
+    switch (attachments[i]) {
+      case GL_DEPTH_ATTACHMENT: {
+        Texture& t = ctx->textures[fb->depth_attachment];
+        t.set_cleared(false);
+        break;
+      }
+      case GL_COLOR_ATTACHMENT0: {
+        Texture& t = ctx->textures[fb->color_attachment];
+        t.disable_delayed_clear();
+        break;
+      }
+    }
+  }
+}
+
+void ReadPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format,
+                GLenum type, void* data) {
+  data = get_pixel_pack_buffer_data(data);
+  if (!data) return;
+  Framebuffer* fb = get_framebuffer(GL_READ_FRAMEBUFFER);
+  if (!fb) return;
+  assert(format == GL_RED || format == GL_RGBA || format == GL_RGBA_INTEGER ||
+         format == GL_BGRA || format == GL_RG);
+  Texture& t = ctx->textures[fb->color_attachment];
+  if (!t.buf) return;
+  prepare_texture(t);
+  // debugf("read pixels %d, %d, %d, %d from fb %d with format %x\n", x, y,
+  // width, height, ctx->read_framebuffer_binding, t.internal_format);
+  x -= t.offset.x;
+  y -= t.offset.y;
+  assert(x >= 0 && y >= 0);
+  assert(x + width <= t.width);
+  assert(y + height <= t.height);
+  if (internal_format_for_data(format, type) != t.internal_format) {
+    debugf("mismatched format for read pixels: %x vs %x\n", t.internal_format,
+           internal_format_for_data(format, type));
+    assert(false);
+    return;
+  }
+  // Only support readback conversions that are reversible
+  assert(!format_requires_conversion(format, t.internal_format) ||
+         bytes_for_internal_format(format) == t.bpp());
+  uint8_t* dest = (uint8_t*)data;
+  size_t destStride = width * t.bpp();
+  if (y < 0) {
+    dest += -y * destStride;
+    height += y;
+    y = 0;
+  }
+  if (y + height > t.height) {
+    height = t.height - y;
+  }
+  if (x < 0) {
+    dest += -x * t.bpp();
+    width += x;
+    x = 0;
+  }
+  if (x + width > t.width) {
+    width = t.width - x;
+  }
+  if (width <= 0 || height <= 0) {
+    return;
+  }
+  convert_copy(format, t.internal_format, dest, destStride,
+               (const uint8_t*)t.sample_ptr(x, y, fb->layer), t.stride(), width,
+               height);
+}
+
+void CopyImageSubData(GLuint srcName, GLenum srcTarget, UNUSED GLint srcLevel,
+                      GLint srcX, GLint srcY, GLint srcZ, GLuint dstName,
+                      GLenum dstTarget, UNUSED GLint dstLevel, GLint dstX,
+                      GLint dstY, GLint dstZ, GLsizei srcWidth,
+                      GLsizei srcHeight, GLsizei srcDepth) {
+  assert(srcLevel == 0 && dstLevel == 0);
+  if (srcTarget == GL_RENDERBUFFER) {
+    Renderbuffer& rb = ctx->renderbuffers[srcName];
+    srcName = rb.texture;
+  }
+  if (dstTarget == GL_RENDERBUFFER) {
+    Renderbuffer& rb = ctx->renderbuffers[dstName];
+    dstName = rb.texture;
+  }
+  Texture& srctex = ctx->textures[srcName];
+  if (!srctex.buf) return;
+  prepare_texture(srctex);
+  Texture& dsttex = ctx->textures[dstName];
+  if (!dsttex.buf) return;
+  assert(!dsttex.locked);
+  IntRect skip = {dstX, dstY, dstX + srcWidth, dstY + srcHeight};
+  prepare_texture(dsttex, &skip);
+  assert(srctex.internal_format == dsttex.internal_format);
+  assert(srcWidth >= 0);
+  assert(srcHeight >= 0);
+  assert(srcDepth >= 0);
+  assert(srcX + srcWidth <= srctex.width);
+  assert(srcY + srcHeight <= srctex.height);
+  assert(srcZ + srcDepth <= max(srctex.depth, 1));
+  assert(dstX + srcWidth <= dsttex.width);
+  assert(dstY + srcHeight <= dsttex.height);
+  assert(dstZ + srcDepth <= max(dsttex.depth, 1));
+  int bpp = srctex.bpp();
+  int src_stride = srctex.stride();
+  int dest_stride = dsttex.stride();
+  for (int z = 0; z < srcDepth; z++) {
+    char* dest = dsttex.sample_ptr(dstX, dstY, dstZ + z);
+    char* src = srctex.sample_ptr(srcX, srcY, srcZ + z);
+    for (int y = 0; y < srcHeight; y++) {
+      memcpy(dest, src, srcWidth * bpp);
+      dest += dest_stride;
+      src += src_stride;
+    }
+  }
+}
+
+void CopyTexSubImage3D(GLenum target, UNUSED GLint level, GLint xoffset,
+                       GLint yoffset, GLint zoffset, GLint x, GLint y,
+                       GLsizei width, GLsizei height) {
+  assert(level == 0);
+  Framebuffer* fb = get_framebuffer(GL_READ_FRAMEBUFFER);
+  if (!fb) return;
+  CopyImageSubData(fb->color_attachment, GL_TEXTURE_3D, 0, x, y, fb->layer,
+                   ctx->get_binding(target), GL_TEXTURE_3D, 0, xoffset, yoffset,
+                   zoffset, width, height, 1);
+}
+
+void CopyTexSubImage2D(GLenum target, UNUSED GLint level, GLint xoffset,
+                       GLint yoffset, GLint x, GLint y, GLsizei width,
+                       GLsizei height) {
+  assert(level == 0);
+  Framebuffer* fb = get_framebuffer(GL_READ_FRAMEBUFFER);
+  if (!fb) return;
+  CopyImageSubData(fb->color_attachment, GL_TEXTURE_2D_ARRAY, 0, x, y,
+                   fb->layer, ctx->get_binding(target), GL_TEXTURE_2D_ARRAY, 0,
+                   xoffset, yoffset, 0, width, height, 1);
+}
+
+}  // extern "C"
+
+using ZMask = I32;
+
+static inline PackedRGBA8 convert_zmask(ZMask mask, uint32_t*) {
+  return bit_cast<PackedRGBA8>(mask);
+}
+
+static inline WideR8 convert_zmask(ZMask mask, uint8_t*) {
+  return CONVERT(mask, WideR8);
+}
+
+#if USE_SSE2
+#  define ZMASK_NONE_PASSED 0xFFFF
+#  define ZMASK_ALL_PASSED 0
+static inline uint32_t zmask_code(ZMask mask) {
+  return _mm_movemask_epi8(mask);
+}
+#else
+#  define ZMASK_NONE_PASSED 0xFFFFFFFFU
+#  define ZMASK_ALL_PASSED 0
+static inline uint32_t zmask_code(ZMask mask) {
+  return bit_cast<uint32_t>(CONVERT(mask, U8));
+}
+#endif
+
+// Interprets items in the depth buffer as sign-extended 32-bit depth values
+// instead of as runs. Returns a mask that signals which samples in the given
+// chunk passed or failed the depth test with given Z value.
+template <bool DISCARD, typename Z>
+static ALWAYS_INLINE bool check_depth(Z z, DepthRun* zbuf, ZMask& outmask,
+                                      int span = 4) {
+  // SSE2 does not support unsigned comparison. So ensure Z value is
+  // sign-extended to int32_t.
+  I32 src = I32(z);
+  I32 dest = unaligned_load<I32>(zbuf);
+  // Invert the depth test to check which pixels failed and should be discarded.
+  ZMask mask = ctx->depthfunc == GL_LEQUAL
+                   ?
+                   // GL_LEQUAL: Not(LessEqual) = Greater
+                   ZMask(src > dest)
+                   :
+                   // GL_LESS: Not(Less) = GreaterEqual
+                   ZMask(src >= dest);
+  // Mask off any unused lanes in the span.
+  mask |= ZMask(span) < ZMask{1, 2, 3, 4};
+  if (zmask_code(mask) == ZMASK_NONE_PASSED) {
+    return false;
+  }
+  if (!DISCARD && ctx->depthmask) {
+    unaligned_store(zbuf, (mask & dest) | (~mask & src));
+  }
+  outmask = mask;
+  return true;
+}
+
+static ALWAYS_INLINE I32 packDepth() {
+  return cast(fragment_shader->gl_FragCoord.z * 0xFFFF);
+}
+
+template <typename Z>
+static ALWAYS_INLINE void discard_depth(Z z, DepthRun* zbuf, I32 mask) {
+  if (ctx->depthmask) {
+    I32 src = I32(z);
+    I32 dest = unaligned_load<I32>(zbuf);
+    mask |= fragment_shader->swgl_IsPixelDiscarded;
+    unaligned_store(zbuf, (mask & dest) | (~mask & src));
+  }
+}
+
+static inline HalfRGBA8 packRGBA8(I32 a, I32 b) {
+#if USE_SSE2
+  return _mm_packs_epi32(a, b);
+#elif USE_NEON
+  return vcombine_u16(vqmovun_s32(a), vqmovun_s32(b));
+#else
+  return CONVERT(combine(a, b), HalfRGBA8);
+#endif
+}
+
+static inline WideRGBA8 pack_pixels_RGBA8(const vec4& v) {
+  ivec4 i = round_pixel(v);
+  HalfRGBA8 xz = packRGBA8(i.z, i.x);
+  HalfRGBA8 yw = packRGBA8(i.y, i.w);
+  HalfRGBA8 xyzwl = zipLow(xz, yw);
+  HalfRGBA8 xyzwh = zipHigh(xz, yw);
+  HalfRGBA8 lo = zip2Low(xyzwl, xyzwh);
+  HalfRGBA8 hi = zip2High(xyzwl, xyzwh);
+  return combine(lo, hi);
+}
+
+UNUSED static inline WideRGBA8 pack_pixels_RGBA8(const vec4_scalar& v) {
+  I32 i = round_pixel((Float){v.z, v.y, v.x, v.w});
+  HalfRGBA8 c = packRGBA8(i, i);
+  return combine(c, c);
+}
+
+static inline WideRGBA8 pack_pixels_RGBA8() {
+  return pack_pixels_RGBA8(fragment_shader->gl_FragColor);
+}
+
+// Load a partial span > 0 and < 4 pixels.
+template <typename V, typename P>
+static ALWAYS_INLINE V partial_load_span(const P* src, int span) {
+  return bit_cast<V>(
+      (span >= 2
+           ? combine(unaligned_load<V2<P>>(src),
+                     V2<P>{span > 2 ? unaligned_load<P>(src + 2) : P(0), 0})
+           : V4<P>{unaligned_load<P>(src), 0, 0, 0}));
+}
+
+// Store a partial span > 0 and < 4 pixels.
+template <typename V, typename P>
+static ALWAYS_INLINE void partial_store_span(P* dst, V src, int span) {
+  auto pixels = bit_cast<V4<P>>(src);
+  if (span >= 2) {
+    unaligned_store(dst, lowHalf(pixels));
+    if (span > 2) {
+      unaligned_store(dst + 2, pixels.z);
+    }
+  } else {
+    unaligned_store(dst, pixels.x);
+  }
+}
+
+// Dispatcher that chooses when to load a full or partial span
+template <typename V, typename P>
+static ALWAYS_INLINE V load_span(const P* src, int span) {
+  if (span >= 4) {
+    return unaligned_load<V, P>(src);
+  } else {
+    return partial_load_span<V, P>(src, span);
+  }
+}
+
+// Dispatcher that chooses when to store a full or partial span
+template <typename V, typename P>
+static ALWAYS_INLINE void store_span(P* dst, V src, int span) {
+  if (span >= 4) {
+    unaligned_store<V, P>(dst, src);
+  } else {
+    partial_store_span<V, P>(dst, src, span);
+  }
+}
+
+// (x*y + x) >> 8, cheap approximation of (x*y) / 255
+template <typename T>
+static inline T muldiv255(T x, T y) {
+  return (x * y + x) >> 8;
+}
+
+// Byte-wise addition for when x or y is a signed 8-bit value stored in the
+// low byte of a larger type T only with zeroed-out high bits, where T is
+// greater than 8 bits, i.e. uint16_t. This can result when muldiv255 is used
+// upon signed operands, using up all the precision in a 16 bit integer, and
+// potentially losing the sign bit in the last >> 8 shift. Due to the
+// properties of two's complement arithmetic, even though we've discarded the
+// sign bit, we can still represent a negative number under addition (without
+// requiring any extra sign bits), just that any negative number will behave
+// like a large unsigned number under addition, generating a single carry bit
+// on overflow that we need to discard. Thus, just doing a byte-wise add will
+// overflow without the troublesome carry, giving us only the remaining 8 low
+// bits we actually need while keeping the high bits at zero.
+template <typename T>
+static inline T addlow(T x, T y) {
+  typedef VectorType<uint8_t, sizeof(T)> bytes;
+  return bit_cast<T>(bit_cast<bytes>(x) + bit_cast<bytes>(y));
+}
+
+static inline WideRGBA8 alphas(WideRGBA8 c) {
+  return SHUFFLE(c, c, 3, 3, 3, 3, 7, 7, 7, 7, 11, 11, 11, 11, 15, 15, 15, 15);
+}
+
+// A pointer into the color buffer for the start of the span.
+static void* swgl_SpanBuf = nullptr;
+// A pointer into the clip mask for the start of the span.
+static uint8_t* swgl_ClipMaskBuf = nullptr;
+
+static ALWAYS_INLINE WideR8 expand_clip_mask(uint8_t* buf, WideR8 mask) {
+  return mask;
+}
+static ALWAYS_INLINE WideRGBA8 expand_clip_mask(uint32_t* buf, WideR8 mask) {
+  WideRG8 maskRG = zip(mask, mask);
+  return zip(maskRG, maskRG);
+}
+
+// Loads a chunk of clip masks. The current pointer into the color buffer is
+// used to reconstruct the relative position within the span. From there, the
+// pointer into the clip mask can be generated from the start of the clip mask
+// span.
+template <typename P>
+static ALWAYS_INLINE auto load_clip_mask(P* buf, int span)
+    -> decltype(expand_clip_mask(buf, 0)) {
+  uint8_t* maskBuf = &swgl_ClipMaskBuf[buf - (P*)swgl_SpanBuf];
+  return expand_clip_mask(buf, unpack(load_span<PackedR8>(maskBuf, span)));
+}
+
+static inline WideRGBA8 blend_pixels(uint32_t* buf, PackedRGBA8 pdst,
+                                     WideRGBA8 src, int span = 4) {
+  WideRGBA8 dst = unpack(pdst);
+  const WideRGBA8 RGB_MASK = {0xFFFF, 0xFFFF, 0xFFFF, 0,      0xFFFF, 0xFFFF,
+                              0xFFFF, 0,      0xFFFF, 0xFFFF, 0xFFFF, 0,
+                              0xFFFF, 0xFFFF, 0xFFFF, 0};
+  const WideRGBA8 ALPHA_MASK = {0, 0, 0, 0xFFFF, 0, 0, 0, 0xFFFF,
+                                0, 0, 0, 0xFFFF, 0, 0, 0, 0xFFFF};
+  const WideRGBA8 ALPHA_OPAQUE = {0, 0, 0, 255, 0, 0, 0, 255,
+                                  0, 0, 0, 255, 0, 0, 0, 255};
+
+  // Each blend case is preceded by the MASK_ variant. The MASK_ case first
+  // loads the mask values and multiplies the source value by them. After, it
+  // falls through to the normal blending case using the masked source.
+#define BLEND_CASE_KEY(key)                                     \
+  MASK_##key : src = muldiv255(src, load_clip_mask(buf, span)); \
+  FALLTHROUGH;                                                  \
+  case key
+#define BLEND_CASE(...) BLEND_CASE_KEY(BLEND_KEY(__VA_ARGS__))
+
+  switch (blend_key) {
+    case BLEND_CASE(GL_ONE, GL_ZERO):
+      return src;
+    case BLEND_CASE(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA, GL_ONE,
+                    GL_ONE_MINUS_SRC_ALPHA):
+      // dst + src.a*(src.rgb1 - dst)
+      // use addlow for signed overflow
+      return addlow(dst, muldiv255(alphas(src), (src | ALPHA_OPAQUE) - dst));
+    case BLEND_CASE(GL_ONE, GL_ONE_MINUS_SRC_ALPHA):
+      return src + dst - muldiv255(dst, alphas(src));
+    case BLEND_CASE(GL_ZERO, GL_ONE_MINUS_SRC_COLOR):
+      return dst - muldiv255(dst, src);
+    case BLEND_CASE(GL_ZERO, GL_ONE_MINUS_SRC_COLOR, GL_ZERO, GL_ONE):
+      return dst - (muldiv255(dst, src) & RGB_MASK);
+    case BLEND_CASE(GL_ZERO, GL_ONE_MINUS_SRC_ALPHA):
+      return dst - muldiv255(dst, alphas(src));
+    case BLEND_CASE(GL_ZERO, GL_SRC_COLOR):
+      return muldiv255(src, dst);
+    case BLEND_CASE(GL_ONE, GL_ONE):
+      return src + dst;
+    case BLEND_CASE(GL_ONE, GL_ONE, GL_ONE, GL_ONE_MINUS_SRC_ALPHA):
+      return src + dst - (muldiv255(dst, src) & ALPHA_MASK);
+    case BLEND_CASE(GL_ONE_MINUS_DST_ALPHA, GL_ONE, GL_ZERO, GL_ONE):
+      // src*(1-dst.a) + dst*1 = src - src*dst.a + dst
+      return dst + ((src - muldiv255(src, alphas(dst))) & RGB_MASK);
+    case BLEND_CASE(GL_CONSTANT_COLOR, GL_ONE_MINUS_SRC_COLOR):
+      // src*k + (1-src)*dst = src*k + dst -
+      // src*dst = dst + src*(k - dst) use addlow
+      // for signed overflow
+      return addlow(
+          dst, muldiv255(src, combine(ctx->blendcolor, ctx->blendcolor) - dst));
+    case BLEND_KEY(GL_ONE, GL_ONE_MINUS_SRC1_COLOR): {
+      WideRGBA8 secondary =
+          pack_pixels_RGBA8(fragment_shader->gl_SecondaryFragColor);
+      return src + dst - muldiv255(dst, secondary);
+    }
+    case MASK_BLEND_KEY(GL_ONE, GL_ONE_MINUS_SRC1_COLOR): {
+      // We must explicitly handle the masked secondary blend case.
+      // The secondary color as well as the source must be multiplied by the
+      // mask.
+      WideRGBA8 mask = load_clip_mask(buf, span);
+      WideRGBA8 secondary =
+          pack_pixels_RGBA8(fragment_shader->gl_SecondaryFragColor);
+      return muldiv255(src, mask) + dst -
+             muldiv255(dst, muldiv255(secondary, mask));
+    }
+    default:
+      UNREACHABLE;
+      // return src;
+  }
+
+#undef BLEND_CASE
+#undef BLEND_CASE_KEY
+}
+
+template <bool DISCARD, int SPAN>
+static ALWAYS_INLINE void discard_output(uint32_t* buf, PackedRGBA8 mask) {
+  WideRGBA8 r = pack_pixels_RGBA8();
+  PackedRGBA8 dst = load_span<PackedRGBA8>(buf, SPAN);
+  if (blend_key) r = blend_pixels(buf, dst, r, SPAN);
+  if (DISCARD)
+    mask |= bit_cast<PackedRGBA8>(fragment_shader->swgl_IsPixelDiscarded);
+  store_span(buf, (mask & dst) | (~mask & pack(r)), SPAN);
+}
+
+template <bool DISCARD, int SPAN>
+static ALWAYS_INLINE void discard_output(uint32_t* buf) {
+  WideRGBA8 r = pack_pixels_RGBA8();
+  if (DISCARD) {
+    PackedRGBA8 dst = load_span<PackedRGBA8>(buf, SPAN);
+    if (blend_key) r = blend_pixels(buf, dst, r, SPAN);
+    PackedRGBA8 mask =
+        bit_cast<PackedRGBA8>(fragment_shader->swgl_IsPixelDiscarded);
+    store_span(buf, (mask & dst) | (~mask & pack(r)), SPAN);
+  } else {
+    if (blend_key)
+      r = blend_pixels(buf, load_span<PackedRGBA8>(buf, SPAN), r, SPAN);
+    store_span(buf, pack(r), SPAN);
+  }
+}
+
+static inline WideR8 packR8(I32 a) {
+#if USE_SSE2
+  return lowHalf(bit_cast<V8<uint16_t>>(_mm_packs_epi32(a, a)));
+#elif USE_NEON
+  return vqmovun_s32(a);
+#else
+  return CONVERT(a, WideR8);
+#endif
+}
+
+static inline WideR8 pack_pixels_R8(Float c) { return packR8(round_pixel(c)); }
+
+static inline WideR8 pack_pixels_R8() {
+  return pack_pixels_R8(fragment_shader->gl_FragColor.x);
+}
+
+static inline WideR8 blend_pixels(uint8_t* buf, WideR8 dst, WideR8 src,
+                                  int span = 4) {
+#define BLEND_CASE_KEY(key)                                     \
+  MASK_##key : src = muldiv255(src, load_clip_mask(buf, span)); \
+  FALLTHROUGH;                                                  \
+  case key
+#define BLEND_CASE(...) BLEND_CASE_KEY(BLEND_KEY(__VA_ARGS__))
+
+  switch (blend_key) {
+    case BLEND_CASE(GL_ONE, GL_ZERO):
+      return src;
+    case BLEND_CASE(GL_ZERO, GL_SRC_COLOR):
+      return muldiv255(src, dst);
+    case BLEND_CASE(GL_ONE, GL_ONE):
+      return src + dst;
+    default:
+      UNREACHABLE;
+      // return src;
+  }
+
+#undef BLEND_CASE
+#undef BLEND_CASE_KEY
+}
+
+template <bool DISCARD, int SPAN>
+static inline void discard_output(uint8_t* buf, WideR8 mask) {
+  WideR8 r = pack_pixels_R8();
+  WideR8 dst = unpack(load_span<PackedR8>(buf, SPAN));
+  if (blend_key) r = blend_pixels(buf, dst, r, SPAN);
+  if (DISCARD) mask |= packR8(fragment_shader->swgl_IsPixelDiscarded);
+  store_span(buf, pack((mask & dst) | (~mask & r)), SPAN);
+}
+
+template <bool DISCARD, int SPAN>
+static inline void discard_output(uint8_t* buf) {
+  WideR8 r = pack_pixels_R8();
+  if (DISCARD) {
+    WideR8 dst = unpack(load_span<PackedR8>(buf, SPAN));
+    if (blend_key) r = blend_pixels(buf, dst, r, SPAN);
+    WideR8 mask = packR8(fragment_shader->swgl_IsPixelDiscarded);
+    store_span(buf, pack((mask & dst) | (~mask & r)), SPAN);
+  } else {
+    if (blend_key)
+      r = blend_pixels(buf, unpack(load_span<PackedR8>(buf, SPAN)), r, SPAN);
+    store_span(buf, pack(r), SPAN);
+  }
+}
+
+template <bool DISCARD, bool W, typename P, typename M>
+static inline void commit_output(P* buf, M mask) {
+  fragment_shader->run<W>();
+  discard_output<DISCARD, 4>(buf, mask);
+}
+
+template <bool DISCARD, bool W, typename P, typename M>
+static inline void commit_output(P* buf, M mask, int span) {
+  fragment_shader->run<W>();
+  switch (span) {
+    case 1:
+      discard_output<DISCARD, 1>(buf, mask);
+      break;
+    case 2:
+      discard_output<DISCARD, 2>(buf, mask);
+      break;
+    default:
+      discard_output<DISCARD, 3>(buf, mask);
+      break;
+  }
+}
+
+template <bool DISCARD, bool W, typename P>
+static inline void commit_output(P* buf) {
+  fragment_shader->run<W>();
+  discard_output<DISCARD, 4>(buf);
+}
+
+template <bool DISCARD, bool W, typename P>
+static inline void commit_output(P* buf, int span) {
+  fragment_shader->run<W>();
+  switch (span) {
+    case 1:
+      discard_output<DISCARD, 1>(buf);
+      break;
+    case 2:
+      discard_output<DISCARD, 2>(buf);
+      break;
+    default:
+      discard_output<DISCARD, 3>(buf);
+      break;
+  }
+}
+
+template <bool DISCARD, bool W, typename P, typename Z>
+static inline void commit_output(P* buf, Z z, DepthRun* zbuf) {
+  ZMask zmask;
+  if (check_depth<DISCARD>(z, zbuf, zmask)) {
+    commit_output<DISCARD, W>(buf, convert_zmask(zmask, buf));
+    if (DISCARD) {
+      discard_depth(z, zbuf, zmask);
+    }
+  } else {
+    fragment_shader->skip<W>();
+  }
+}
+
+template <bool DISCARD, bool W, typename P, typename Z>
+static inline void commit_output(P* buf, Z z, DepthRun* zbuf, int span) {
+  ZMask zmask;
+  if (check_depth<DISCARD>(z, zbuf, zmask, span)) {
+    commit_output<DISCARD, W>(buf, convert_zmask(zmask, buf), span);
+    if (DISCARD) {
+      discard_depth(z, zbuf, zmask);
+    }
+  }
+}
+
+#include "composite.h"
+#include "swgl_ext.h"
+
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wuninitialized"
+#pragma GCC diagnostic ignored "-Wunused-function"
+#pragma GCC diagnostic ignored "-Wunused-parameter"
+#pragma GCC diagnostic ignored "-Wunused-variable"
+#pragma GCC diagnostic ignored "-Wimplicit-fallthrough"
+#ifdef __clang__
+#  pragma GCC diagnostic ignored "-Wunused-private-field"
+#else
+#  pragma GCC diagnostic ignored "-Wunused-but-set-variable"
+#endif
+#include "load_shader.h"
+#pragma GCC diagnostic pop
+
+typedef vec2_scalar Point2D;
+typedef vec4_scalar Point3D;
+
+struct ClipRect {
+  float x0;
+  float y0;
+  float x1;
+  float y1;
+
+  explicit ClipRect(const IntRect& i)
+      : x0(i.x0), y0(i.y0), x1(i.x1), y1(i.y1) {}
+  explicit ClipRect(const Texture& t) : ClipRect(ctx->apply_scissor(t)) {
+    // If blending is enabled, set blend_key to reflect the resolved blend
+    // state for the currently drawn primitive.
+    if (ctx->blend) {
+      blend_key = ctx->blend_key;
+      // If a clip mask is available, set up blending state to use the clip
+      // mask.
+      if (swgl_ClipMask) {
+        assert(swgl_ClipMask->format == TextureFormat::R8);
+        // Constrain the clip mask bounds to always fall within the clip mask.
+        swgl_ClipMaskBounds.intersect(IntRect{0, 0, int(swgl_ClipMask->width),
+                                              int(swgl_ClipMask->height)});
+        // The clip mask offset is relative to the viewport.
+        swgl_ClipMaskOffset += ctx->viewport.origin() - t.offset;
+        // The clip mask bounds are relative to the clip mask offset.
+        swgl_ClipMaskBounds.offset(swgl_ClipMaskOffset);
+        // Finally, constrain the clip rectangle by the clip mask bounds.
+        intersect(swgl_ClipMaskBounds);
+        // Modify the blend key so that it will use the clip mask while
+        // blending.
+        blend_key = BlendKey(MASK_BLEND_KEY_NONE + blend_key);
+      }
+    } else {
+      blend_key = BLEND_KEY_NONE;
+    }
+  }
+
+  void intersect(const IntRect& c) {
+    x0 = max(x0, float(c.x0));
+    y0 = max(y0, float(c.y0));
+    x1 = min(x1, float(c.x1));
+    y1 = min(y1, float(c.y1));
+  }
+
+  template <typename P>
+  void init_span(int x, int y, P* buf) const {
+    if (blend_key >= MASK_BLEND_KEY_NONE) {
+      swgl_SpanBuf = buf;
+      swgl_ClipMaskBuf = (uint8_t*)swgl_ClipMask->buf +
+                         (y - swgl_ClipMaskOffset.y) * swgl_ClipMask->stride +
+                         (x - swgl_ClipMaskOffset.x);
+    }
+  }
+
+  template <typename P>
+  bool overlaps(int nump, const P* p) const {
+    // Generate a mask of which side of the clip rect all of a polygon's points
+    // fall inside of. This is a cheap conservative estimate of whether the
+    // bounding box of the polygon might overlap the clip rect, rather than an
+    // exact test that would require multiple slower line intersections.
+    int sides = 0;
+    for (int i = 0; i < nump; i++) {
+      sides |= p[i].x < x1 ? (p[i].x > x0 ? 1 | 2 : 1) : 2;
+      sides |= p[i].y < y1 ? (p[i].y > y0 ? 4 | 8 : 4) : 8;
+    }
+    return sides == 0xF;
+  }
+};
+
+// Converts a run array into a flattened array of depth samples. This just
+// walks through every run and fills the samples with the depth value from
+// the run.
+static void flatten_depth_runs(DepthRun* runs, size_t width) {
+  if (runs->is_flat()) {
+    return;
+  }
+  while (width > 0) {
+    size_t n = runs->count;
+    fill_depth_run(runs, n, runs->depth);
+    runs += n;
+    width -= n;
+  }
+}
+
+// Helper function for drawing passed depth runs within the depth buffer.
+// Flattened depth (perspective or discard) is not supported.
+template <typename P>
+static ALWAYS_INLINE void draw_depth_span(uint16_t z, P* buf,
+                                          DepthCursor& cursor) {
+  for (;;) {
+    // Get the span that passes the depth test. Assume on entry that
+    // any failed runs have already been skipped.
+    int span = cursor.check_passed(z, ctx->depthfunc, ctx->depthmask);
+    // If nothing passed, since we already skipped passed failed runs
+    // previously, we must have hit the end of the row. Bail out.
+    if (span <= 0) {
+      break;
+    }
+    if (span >= 4) {
+      // If we have a draw specialization, try to process as many 4-pixel
+      // chunks as possible using it.
+      if (fragment_shader->has_draw_span(buf)) {
+        int len = span & ~3;
+        fragment_shader->draw_span(buf, len);
+        buf += len;
+        span &= 3;
+      } else {
+        // Otherwise, just process each chunk individually.
+        while (span >= 4) {
+          commit_output<false, false>(buf);
+          buf += 4;
+          span -= 4;
+        }
+      }
+    }
+    // If we have a partial chunk left over, we still have to process it as if
+    // it were a full chunk. Mask off only the part of the chunk we want to
+    // use.
+    if (span > 0) {
+      commit_output<false, false>(buf, span);
+      buf += span;
+    }
+    // Skip past any runs that fail the depth test.
+    int skip = cursor.skip_failed(z, ctx->depthfunc);
+    // If there aren't any, that means we won't encounter any more passing runs
+    // and so it's safe to bail out.
+    if (skip <= 0) {
+      break;
+    }
+    // Advance interpolants for the fragment shader past the skipped region.
+    // If we processed a partial chunk above, we actually advanced the
+    // interpolants a full chunk in the fragment shader's run function. Thus,
+    // we need to first subtract off that 4-pixel chunk and only partially
+    // advance them to that partial chunk before we can add on the rest of the
+    // skips. This is combined with the skip here for efficiency's sake.
+    fragment_shader->skip(skip - (span > 0 ? 4 - span : 0));
+    buf += skip;
+  }
+}
+
+// Draw a simple span in 4-pixel wide chunks, optionally using depth.
+template <bool DISCARD, bool W, typename P, typename Z>
+static ALWAYS_INLINE void draw_span(P* buf, DepthRun* depth, int span, Z z) {
+  if (depth) {
+    // Depth testing is enabled. If perspective is used, Z values will vary
+    // across the span, we use packDepth to generate 16-bit Z values suitable
+    // for depth testing based on current values from gl_FragCoord.z.
+    // Otherwise, for the no-perspective case, we just use the provided Z.
+    // Process 4-pixel chunks first.
+    for (; span >= 4; span -= 4, buf += 4, depth += 4) {
+      commit_output<DISCARD, W>(buf, z(), depth);
+    }
+    // If there are any remaining pixels, do a partial chunk.
+    if (span > 0) {
+      commit_output<DISCARD, W>(buf, z(), depth, span);
+    }
+  } else {
+    // Process 4-pixel chunks first.
+    for (; span >= 4; span -= 4, buf += 4) {
+      commit_output<DISCARD, W>(buf);
+    }
+    // If there are any remaining pixels, do a partial chunk.
+    if (span > 0) {
+      commit_output<DISCARD, W>(buf, span);
+    }
+  }
+}
+
+// Called during rasterization to forcefully clear a row on which delayed clear
+// has been enabled. If we know that we are going to completely overwrite a part
+// of the row, then we only need to clear the row outside of that part. However,
+// if blending or discard is enabled, the values of that underlying part of the
+// row may be used regardless to produce the final rasterization result, so we
+// have to then clear the entire underlying row to prepare it.
+template <typename P>
+static inline void prepare_row(Texture& colortex, int y, int startx, int endx,
+                               bool use_discard, DepthRun* depth,
+                               uint16_t z = 0, DepthCursor* cursor = nullptr) {
+  assert(colortex.delay_clear > 0);
+  // Delayed clear is enabled for the color buffer. Check if needs clear.
+  uint32_t& mask = colortex.cleared_rows[y / 32];
+  if ((mask & (1 << (y & 31))) == 0) {
+    mask |= 1 << (y & 31);
+    colortex.delay_clear--;
+    if (blend_key || use_discard) {
+      // If depth test, blending, or discard is used, old color values
+      // might be sampled, so we need to clear the entire row to fill it.
+      force_clear_row<P>(colortex, y);
+    } else if (depth) {
+      if (depth->is_flat() || !cursor) {
+        // If flat depth is used, we can't cheaply predict if which samples will
+        // pass.
+        force_clear_row<P>(colortex, y);
+      } else {
+        // Otherwise if depth runs are used, see how many samples initially pass
+        // the depth test and only fill the row outside those. The fragment
+        // shader will fill the row within the passed samples.
+        int passed =
+            DepthCursor(*cursor).check_passed<false>(z, ctx->depthfunc);
+        if (startx > 0 || startx + passed < colortex.width) {
+          force_clear_row<P>(colortex, y, startx, startx + passed);
+        }
+      }
+    } else if (startx > 0 || endx < colortex.width) {
+      // Otherwise, we only need to clear the row outside of the span.
+      // The fragment shader will fill the row within the span itself.
+      force_clear_row<P>(colortex, y, startx, endx);
+    }
+  }
+}
+
+// Draw spans for each row of a given quad (or triangle) with a constant Z
+// value. The quad is assumed convex. It is clipped to fall within the given
+// clip rect. In short, this function rasterizes a quad by first finding a
+// top most starting point and then from there tracing down the left and right
+// sides of this quad until it hits the bottom, outputting a span between the
+// current left and right positions at each row along the way. Points are
+// assumed to be ordered in either CW or CCW to support this, but currently
+// both orders (CW and CCW) are supported and equivalent.
+template <typename P>
+static inline void draw_quad_spans(int nump, Point2D p[4], uint16_t z,
+                                   Interpolants interp_outs[4],
+                                   Texture& colortex, int layer,
+                                   Texture& depthtex,
+                                   const ClipRect& clipRect) {
+  // Only triangles and convex quads supported.
+  assert(nump == 3 || nump == 4);
+  Point2D l0, r0, l1, r1;
+  int l0i, r0i, l1i, r1i;
+  {
+    // Find the index of the top-most (smallest Y) point from which
+    // rasterization can start.
+    int top = nump > 3 && p[3].y < p[2].y
+                  ? (p[0].y < p[1].y ? (p[0].y < p[3].y ? 0 : 3)
+                                     : (p[1].y < p[3].y ? 1 : 3))
+                  : (p[0].y < p[1].y ? (p[0].y < p[2].y ? 0 : 2)
+                                     : (p[1].y < p[2].y ? 1 : 2));
+    // Helper to find next index in the points array, walking forward.
+#define NEXT_POINT(idx)   \
+  ({                      \
+    int cur = (idx) + 1;  \
+    cur < nump ? cur : 0; \
+  })
+    // Helper to find the previous index in the points array, walking backward.
+#define PREV_POINT(idx)        \
+  ({                           \
+    int cur = (idx)-1;         \
+    cur >= 0 ? cur : nump - 1; \
+  })
+    // Start looking for "left"-side and "right"-side descending edges starting
+    // from the determined top point.
+    int next = NEXT_POINT(top);
+    int prev = PREV_POINT(top);
+    if (p[top].y == p[next].y) {
+      // If the next point is on the same row as the top, then advance one more
+      // time to the next point and use that as the "left" descending edge.
+      l0i = next;
+      l1i = NEXT_POINT(next);
+      // Assume top and prev form a descending "right" edge, as otherwise this
+      // will be a collapsed polygon and harmlessly bail out down below.
+      r0i = top;
+      r1i = prev;
+    } else if (p[top].y == p[prev].y) {
+      // If the prev point is on the same row as the top, then advance to the
+      // prev again and use that as the "right" descending edge.
+      // Assume top and next form a non-empty descending "left" edge.
+      l0i = top;
+      l1i = next;
+      r0i = prev;
+      r1i = PREV_POINT(prev);
+    } else {
+      // Both next and prev are on distinct rows from top, so both "left" and
+      // "right" edges are non-empty/descending.
+      l0i = r0i = top;
+      l1i = next;
+      r1i = prev;
+    }
+    // Load the points from the indices.
+    l0 = p[l0i];  // Start of left edge
+    r0 = p[r0i];  // End of left edge
+    l1 = p[l1i];  // Start of right edge
+    r1 = p[r1i];  // End of right edge
+    //    debugf("l0: %d(%f,%f), r0: %d(%f,%f) -> l1: %d(%f,%f), r1:
+    //    %d(%f,%f)\n", l0i, l0.x, l0.y, r0i, r0.x, r0.y, l1i, l1.x, l1.y, r1i,
+    //    r1.x, r1.y);
+  }
+
+  struct Edge {
+    float yScale;
+    float xSlope;
+    float x;
+    Interpolants interpSlope;
+    Interpolants interp;
+
+    Edge(float y, const Point2D& p0, const Point2D& p1, const Interpolants& i0,
+         const Interpolants& i1)
+        :  // Inverse Y scale for slope calculations. Avoid divide on 0-length
+           // edge. Later checks below ensure that Y <= p1.y, or otherwise we
+           // don't use this edge. We just need to guard against Y == p1.y ==
+           // p0.y. In that case, Y - p0.y == 0 and will cancel out the slopes
+           // below, except if yScale is Inf for some reason (or worse, NaN),
+           // which 1/(p1.y-p0.y) might produce if we don't bound it.
+          yScale(1.0f / max(p1.y - p0.y, 1.0f / 256)),
+          // Calculate dX/dY slope
+          xSlope((p1.x - p0.x) * yScale),
+          // Initialize current X based on Y and slope
+          x(p0.x + (y - p0.y) * xSlope),
+          // Calculate change in interpolants per change in Y
+          interpSlope((i1 - i0) * yScale),
+          // Initialize current interpolants based on Y and slope
+          interp(i0 + (y - p0.y) * interpSlope) {}
+
+    void nextRow() {
+      // step current X and interpolants to next row from slope
+      x += xSlope;
+      interp += interpSlope;
+    }
+  };
+
+  // Vertex selection above should result in equal left and right start rows
+  assert(l0.y == r0.y);
+  // Find the start y, clip to within the clip rect, and round to row center.
+  float y = floor(max(l0.y, clipRect.y0) + 0.5f) + 0.5f;
+  // Initialize left and right edges from end points and start Y
+  Edge left(y, l0, l1, interp_outs[l0i], interp_outs[l1i]);
+  Edge right(y, r0, r1, interp_outs[r0i], interp_outs[r1i]);
+  // Get pointer to color buffer and depth buffer at current Y
+  P* fbuf = (P*)colortex.sample_ptr(0, int(y), layer);
+  DepthRun* fdepth = (DepthRun*)depthtex.sample_ptr(0, int(y));
+  // Loop along advancing Ys, rasterizing spans at each row
+  float checkY = min(min(l1.y, r1.y), clipRect.y1);
+  for (;;) {
+    // Check if we maybe passed edge ends or outside clip rect...
+    if (y > checkY) {
+      // If we're outside the clip rect, we're done.
+      if (y > clipRect.y1) break;
+        // Helper to find the next non-duplicate vertex that doesn't loop back.
+#define STEP_EDGE(e0i, e0, e1i, e1, STEP_POINT, end)               \
+  for (;;) {                                                       \
+    /* Set new start of edge to be end of old edge */              \
+    e0i = e1i;                                                     \
+    e0 = e1;                                                       \
+    /* Set new end of edge to next point */                        \
+    e1i = STEP_POINT(e1i);                                         \
+    e1 = p[e1i];                                                   \
+    /* If the edge is descending, use it. */                       \
+    if (e1.y > e0.y) break;                                        \
+    /* If the edge is ascending or crossed the end, we're done. */ \
+    if (e1.y < e0.y || e0i == end) return;                         \
+    /* Otherwise, it's a duplicate, so keep searching. */          \
+  }
+      // Check if Y advanced past the end of the left edge
+      if (y > l1.y) {
+        // Step to next left edge past Y and reset edge interpolants.
+        do {
+          STEP_EDGE(l0i, l0, l1i, l1, NEXT_POINT, r1i);
+        } while (y > l1.y);
+        left = Edge(y, l0, l1, interp_outs[l0i], interp_outs[l1i]);
+      }
+      // Check if Y advanced past the end of the right edge
+      if (y > r1.y) {
+        // Step to next right edge past Y and reset edge interpolants.
+        do {
+          STEP_EDGE(r0i, r0, r1i, r1, PREV_POINT, l1i);
+        } while (y > r1.y);
+        right = Edge(y, r0, r1, interp_outs[r0i], interp_outs[r1i]);
+      }
+      // Reset check condition for next time around.
+      checkY = min(min(l1.y, r1.y), clipRect.y1);
+    }
+    // lx..rx form the bounds of the span. WR does not use backface culling,
+    // so we need to use min/max to support the span in either orientation.
+    // Clip the span to fall within the clip rect and then round to nearest
+    // column.
+    int startx = int(max(min(left.x, right.x), clipRect.x0) + 0.5f);
+    int endx = int(min(max(left.x, right.x), clipRect.x1) + 0.5f);
+    // Check if span is non-empty.
+    int span = endx - startx;
+    if (span > 0) {
+      ctx->shaded_rows++;
+      ctx->shaded_pixels += span;
+      // Advance color/depth buffer pointers to the start of the span.
+      P* buf = fbuf + startx;
+      // Check if the we will need to use depth-buffer or discard on this span.
+      DepthRun* depth =
+          depthtex.buf != nullptr && depthtex.cleared() ? fdepth : nullptr;
+      DepthCursor cursor;
+      bool use_discard = fragment_shader->use_discard();
+      if (use_discard) {
+        if (depth) {
+          // If we're using discard, we may have to unpredictably drop out some
+          // samples. Flatten the depth run array here to allow this.
+          if (!depth->is_flat()) {
+            flatten_depth_runs(depth, depthtex.width);
+          }
+          // Advance to the depth sample at the start of the span.
+          depth += startx;
+        }
+      } else if (depth) {
+        if (!depth->is_flat()) {
+          // We're not using discard and the depth row is still organized into
+          // runs. Skip past any runs that would fail the depth test so we
+          // don't have to do any extra work to process them with the rest of
+          // the span.
+          cursor = DepthCursor(depth, depthtex.width, startx, span);
+          int skipped = cursor.skip_failed(z, ctx->depthfunc);
+          // If we fell off the row, that means we couldn't find any passing
+          // runs. We can just skip the entire span.
+          if (skipped < 0) {
+            goto next_span;
+          }
+          buf += skipped;
+          startx += skipped;
+          span -= skipped;
+        } else {
+          // The row is already flattened, so just advance to the span start.
+          depth += startx;
+        }
+      }
+
+      if (colortex.delay_clear) {
+        // Delayed clear is enabled for the color buffer. Check if needs clear.
+        prepare_row<P>(colortex, int(y), startx, endx, use_discard, depth, z,
+                       &cursor);
+      }
+
+      // Initialize fragment shader interpolants to current span position.
+      fragment_shader->gl_FragCoord.x = init_interp(startx + 0.5f, 1);
+      fragment_shader->gl_FragCoord.y = y;
+      {
+        // Change in interpolants is difference between current right and left
+        // edges per the change in right and left X.
+        Interpolants step =
+            (right.interp - left.interp) * (1.0f / (right.x - left.x));
+        // Advance current interpolants to X at start of span.
+        Interpolants o = left.interp + step * (startx + 0.5f - left.x);
+        fragment_shader->init_span(&o, &step);
+      }
+      clipRect.init_span(startx, y, buf);
+      if (!use_discard) {
+        // Fast paths for the case where fragment discard is not used.
+        if (depth) {
+          // If depth is used, we want to process entire depth runs if depth is
+          // not flattened.
+          if (!depth->is_flat()) {
+            draw_depth_span(z, buf, cursor);
+            goto next_span;
+          }
+          // Otherwise, flattened depth must fall back to the slightly slower
+          // per-chunk depth test path in draw_span below.
+        } else {
+          // Check if the fragment shader has an optimized draw specialization.
+          if (span >= 4 && fragment_shader->has_draw_span(buf)) {
+            // Draw specialization expects 4-pixel chunks.
+            int len = span & ~3;
+            fragment_shader->draw_span(buf, len);
+            buf += len;
+            span &= 3;
+          }
+        }
+        draw_span<false, false>(buf, depth, span, [=] { return z; });
+      } else {
+        // If discard is used, then use slower fallbacks. This should be rare.
+        // Just needs to work, doesn't need to be too fast yet...
+        draw_span<true, false>(buf, depth, span, [=] { return z; });
+      }
+    }
+  next_span:
+    // Advance Y and edge interpolants to next row.
+    y++;
+    left.nextRow();
+    right.nextRow();
+    // Advance buffers to next row.
+    fbuf += colortex.stride() / sizeof(P);
+    fdepth += depthtex.stride() / sizeof(DepthRun);
+  }
+}
+
+// Draw perspective-correct spans for a convex quad that has been clipped to
+// the near and far Z planes, possibly producing a clipped convex polygon with
+// more than 4 sides. This assumes the Z value will vary across the spans and
+// requires interpolants to factor in W values. This tends to be slower than
+// the simpler 2D draw_quad_spans above, especially since we can't optimize the
+// depth test easily when Z values, and should be used only rarely if possible.
+template <typename P>
+static inline void draw_perspective_spans(int nump, Point3D* p,
+                                          Interpolants* interp_outs,
+                                          Texture& colortex, int layer,
+                                          Texture& depthtex,
+                                          const ClipRect& clipRect) {
+  Point3D l0, r0, l1, r1;
+  int l0i, r0i, l1i, r1i;
+  {
+    // Find the index of the top-most point (smallest Y) from which
+    // rasterization can start.
+    int top = 0;
+    for (int i = 1; i < nump; i++) {
+      if (p[i].y < p[top].y) {
+        top = i;
+      }
+    }
+    // Find left-most top point, the start of the left descending edge.
+    // Advance forward in the points array, searching at most nump points
+    // in case the polygon is flat.
+    l0i = top;
+    for (int i = top + 1; i < nump && p[i].y == p[top].y; i++) {
+      l0i = i;
+    }
+    if (l0i == nump - 1) {
+      for (int i = 0; i <= top && p[i].y == p[top].y; i++) {
+        l0i = i;
+      }
+    }
+    // Find right-most top point, the start of the right descending edge.
+    // Advance backward in the points array, searching at most nump points.
+    r0i = top;
+    for (int i = top - 1; i >= 0 && p[i].y == p[top].y; i--) {
+      r0i = i;
+    }
+    if (r0i == 0) {
+      for (int i = nump - 1; i >= top && p[i].y == p[top].y; i--) {
+        r0i = i;
+      }
+    }
+    // End of left edge is next point after left edge start.
+    l1i = NEXT_POINT(l0i);
+    // End of right edge is prev point after right edge start.
+    r1i = PREV_POINT(r0i);
+    l0 = p[l0i];  // Start of left edge
+    r0 = p[r0i];  // End of left edge
+    l1 = p[l1i];  // Start of right edge
+    r1 = p[r1i];  // End of right edge
+  }
+
+  struct Edge {
+    float yScale;
+    // Current coordinates for edge. Where in the 2D case of draw_quad_spans,
+    // it is enough to just track the X coordinate as we advance along the rows,
+    // for the perspective case we also need to keep track of Z and W. For
+    // simplicity, we just use the full 3D point to track all these coordinates.
+    Point3D pSlope;
+    Point3D p;
+    Interpolants interpSlope;
+    Interpolants interp;
+
+    Edge(float y, const Point3D& p0, const Point3D& p1, const Interpolants& i0,
+         const Interpolants& i1)
+        :  // Inverse Y scale for slope calculations. Avoid divide on 0-length
+           // edge.
+          yScale(1.0f / max(p1.y - p0.y, 1.0f / 256)),
+          // Calculate dX/dY slope
+          pSlope((p1 - p0) * yScale),
+          // Initialize current coords based on Y and slope
+          p(p0 + (y - p0.y) * pSlope),
+          // Crucially, these interpolants must be scaled by the point's 1/w
+          // value, which allows linear interpolation in a perspective-correct
+          // manner. This will be canceled out inside the fragment shader later.
+          // Calculate change in interpolants per change in Y
+          interpSlope((i1 * p1.w - i0 * p0.w) * yScale),
+          // Initialize current interpolants based on Y and slope
+          interp(i0 * p0.w + (y - p0.y) * interpSlope) {}
+
+    float x() const { return p.x; }
+    vec2_scalar zw() const { return {p.z, p.w}; }
+
+    void nextRow() {
+      // step current coords and interpolants to next row from slope
+      p += pSlope;
+      interp += interpSlope;
+    }
+  };
+
+  // Vertex selection above should result in equal left and right start rows
+  assert(l0.y == r0.y);
+  // Find the start y, clip to within the clip rect, and round to row center.
+  float y = floor(max(l0.y, clipRect.y0) + 0.5f) + 0.5f;
+  // Initialize left and right edges from end points and start Y
+  Edge left(y, l0, l1, interp_outs[l0i], interp_outs[l1i]);
+  Edge right(y, r0, r1, interp_outs[r0i], interp_outs[r1i]);
+  // Get pointer to color buffer and depth buffer at current Y
+  P* fbuf = (P*)colortex.sample_ptr(0, int(y), layer);
+  DepthRun* fdepth = (DepthRun*)depthtex.sample_ptr(0, int(y));
+  // Loop along advancing Ys, rasterizing spans at each row
+  float checkY = min(min(l1.y, r1.y), clipRect.y1);
+  for (;;) {
+    // Check if we maybe passed edge ends or outside clip rect...
+    if (y > checkY) {
+      // If we're outside the clip rect, we're done.
+      if (y > clipRect.y1) break;
+      // Check if Y advanced past the end of the left edge
+      if (y > l1.y) {
+        // Step to next left edge past Y and reset edge interpolants.
+        do {
+          STEP_EDGE(l0i, l0, l1i, l1, NEXT_POINT, r1i);
+        } while (y > l1.y);
+        left = Edge(y, l0, l1, interp_outs[l0i], interp_outs[l1i]);
+      }
+      // Check if Y advanced past the end of the right edge
+      if (y > r1.y) {
+        // Step to next right edge past Y and reset edge interpolants.
+        do {
+          STEP_EDGE(r0i, r0, r1i, r1, PREV_POINT, l1i);
+        } while (y > r1.y);
+        right = Edge(y, r0, r1, interp_outs[r0i], interp_outs[r1i]);
+      }
+      // Reset check condition for next time around.
+      checkY = min(min(l1.y, r1.y), clipRect.y1);
+    }
+    // lx..rx form the bounds of the span. WR does not use backface culling,
+    // so we need to use min/max to support the span in either orientation.
+    // Clip the span to fall within the clip rect and then round to nearest
+    // column.
+    int startx = int(max(min(left.x(), right.x()), clipRect.x0) + 0.5f);
+    int endx = int(min(max(left.x(), right.x()), clipRect.x1) + 0.5f);
+    // Check if span is non-empty.
+    int span = endx - startx;
+    if (span > 0) {
+      ctx->shaded_rows++;
+      ctx->shaded_pixels += span;
+      // Advance color/depth buffer pointers to the start of the span.
+      P* buf = fbuf + startx;
+      // Check if the we will need to use depth-buffer or discard on this span.
+      DepthRun* depth =
+          depthtex.buf != nullptr && depthtex.cleared() ? fdepth : nullptr;
+      bool use_discard = fragment_shader->use_discard();
+      if (depth) {
+        // Perspective may cause the depth value to vary on a per sample basis.
+        // Ensure the depth row is flattened to allow testing of individual
+        // samples
+        if (!depth->is_flat()) {
+          flatten_depth_runs(depth, depthtex.width);
+        }
+        // Advance to the depth sample at the start of the span.
+        depth += startx;
+      }
+      if (colortex.delay_clear) {
+        // Delayed clear is enabled for the color buffer. Check if needs clear.
+        prepare_row<P>(colortex, int(y), startx, endx, use_discard, depth);
+      }
+      // Initialize fragment shader interpolants to current span position.
+      fragment_shader->gl_FragCoord.x = init_interp(startx + 0.5f, 1);
+      fragment_shader->gl_FragCoord.y = y;
+      {
+        // Calculate the fragment Z and W change per change in fragment X step.
+        vec2_scalar stepZW =
+            (right.zw() - left.zw()) * (1.0f / (right.x() - left.x()));
+        // Calculate initial Z and W values for span start.
+        vec2_scalar zw = left.zw() + stepZW * (startx + 0.5f - left.x());
+        // Set fragment shader's Z and W values so that it can use them to
+        // cancel out the 1/w baked into the interpolants.
+        fragment_shader->gl_FragCoord.z = init_interp(zw.x, stepZW.x);
+        fragment_shader->gl_FragCoord.w = init_interp(zw.y, stepZW.y);
+        fragment_shader->swgl_StepZW = stepZW;
+        // Change in interpolants is difference between current right and left
+        // edges per the change in right and left X. The left and right
+        // interpolant values were previously multipled by 1/w, so the step and
+        // initial span values take this into account.
+        Interpolants step =
+            (right.interp - left.interp) * (1.0f / (right.x() - left.x()));
+        // Advance current interpolants to X at start of span.
+        Interpolants o = left.interp + step * (startx + 0.5f - left.x());
+        fragment_shader->init_span<true>(&o, &step);
+      }
+      clipRect.init_span(startx, y, buf);
+      if (!use_discard) {
+        // No discard is used. Common case.
+        draw_span<false, true>(buf, depth, span, packDepth);
+      } else {
+        // Discard is used. Rare.
+        draw_span<true, true>(buf, depth, span, packDepth);
+      }
+    }
+    // Advance Y and edge interpolants to next row.
+    y++;
+    left.nextRow();
+    right.nextRow();
+    // Advance buffers to next row.
+    fbuf += colortex.stride() / sizeof(P);
+    fdepth += depthtex.stride() / sizeof(DepthRun);
+  }
+}
+
+// Clip a primitive against both sides of a view-frustum axis, producing
+// intermediate vertexes with interpolated attributes that will no longer
+// intersect the selected axis planes. This assumes the primitive is convex
+// and should produce at most N+2 vertexes for each invocation (only in the
+// worst case where one point falls outside on each of the opposite sides
+// with the rest of the points inside).
+template <XYZW AXIS>
+static int clip_side(int nump, Point3D* p, Interpolants* interp, Point3D* outP,
+                     Interpolants* outInterp) {
+  // Potential mask bits of which side of a plane a coordinate falls on.
+  enum SIDE { POSITIVE = 1, NEGATIVE = 2 };
+  int numClip = 0;
+  Point3D prev = p[nump - 1];
+  Interpolants prevInterp = interp[nump - 1];
+  float prevCoord = prev.select(AXIS);
+  // Coordinate must satisfy -W <= C <= W. Determine if it is outside, and
+  // if so, remember which side it is outside of. In the special case that W is
+  // negative and |C| < |W|, both -W <= C and C <= W will be false, such that
+  // we must consider the coordinate as falling outside of both plane sides
+  // simultaneously. We test each condition separately and combine them to form
+  // a mask of which plane sides we exceeded. If we neglect to consider both
+  // sides simultaneously, points can erroneously oscillate from one plane side
+  // to the other and exceed the supported maximum number of clip outputs.
+  int prevMask = (prevCoord < -prev.w ? NEGATIVE : 0) |
+                 (prevCoord > prev.w ? POSITIVE : 0);
+  // Loop through points, finding edges that cross the planes by evaluating
+  // the side at each point.
+  for (int i = 0; i < nump; i++) {
+    Point3D cur = p[i];
+    Interpolants curInterp = interp[i];
+    float curCoord = cur.select(AXIS);
+    int curMask =
+        (curCoord < -cur.w ? NEGATIVE : 0) | (curCoord > cur.w ? POSITIVE : 0);
+    // Check if the previous and current end points are on different sides. If
+    // the masks of sides intersect, then we consider them to be on the same
+    // side. So in the case the masks do not intersect, we then consider them
+    // to fall on different sides.
+    if (!(curMask & prevMask)) {
+      // One of the edge's end points is outside the plane with the other
+      // inside the plane. Find the offset where it crosses the plane and
+      // adjust the point and interpolants to there.
+      if (prevMask) {
+        // Edge that was previously outside crosses inside.
+        // Evaluate plane equation for previous and current end-point
+        // based on previous side and calculate relative offset.
+        if (numClip >= nump + 2) {
+          // If for some reason we produced more vertexes than we support, just
+          // bail out.
+          assert(false);
+          return 0;
+        }
+        // The positive plane is assigned the sign 1, and the negative plane is
+        // assigned -1. If the point falls outside both planes, that means W is
+        // negative. To compensate for this, we must interpolate the coordinate
+        // till W=0, at which point we can choose a single plane side for the
+        // coordinate to fall on since W will no longer be negative. To compute
+        // the coordinate where W=0, we compute K = prev.w / (prev.w-cur.w) and
+        // interpolate C = prev.C + K*(cur.C - prev.C). The sign of C will be
+        // the side of the plane we need to consider. Substituting K into the
+        // comparison C < 0, we can then avoid the division in K with a
+        // cross-multiplication.
+        float prevSide =
+            (prevMask & NEGATIVE) && (!(prevMask & POSITIVE) ||
+                                      prevCoord * (cur.w - prev.w) <
+                                          prev.w * (curCoord - prevCoord))
+                ? -1
+                : 1;
+        float prevDist = prevCoord - prevSide * prev.w;
+        float curDist = curCoord - prevSide * cur.w;
+        // It may happen that after we interpolate by the weight k that due to
+        // floating point rounding we've underestimated the value necessary to
+        // push it over the clipping boundary. Just in case, nudge the mantissa
+        // by a single increment so that we essentially round it up and move it
+        // further inside the clipping boundary. We use nextafter to do this in
+        // a portable fashion.
+        float k = prevDist / (prevDist - curDist);
+        Point3D clipped = prev + (cur - prev) * k;
+        if (prevSide * clipped.select(AXIS) > clipped.w) {
+          k = nextafterf(k, 1.0f);
+          clipped = prev + (cur - prev) * k;
+        }
+        outP[numClip] = clipped;
+        outInterp[numClip] = prevInterp + (curInterp - prevInterp) * k;
+        numClip++;
+      }
+      if (curMask) {
+        // Edge that was previously inside crosses outside.
+        // Evaluate plane equation for previous and current end-point
+        // based on current side and calculate relative offset.
+        if (numClip >= nump + 2) {
+          assert(false);
+          return 0;
+        }
+        // In the case the coordinate falls on both plane sides, the computation
+        // here is much the same as for prevSide, but since we are going from a
+        // previous W that is positive to current W that is negative, then the
+        // sign of cur.w - prev.w will flip in the equation. The resulting sign
+        // is negated to compensate for this.
+        float curSide =
+            (curMask & POSITIVE) && (!(curMask & NEGATIVE) ||
+                                     prevCoord * (cur.w - prev.w) <
+                                         prev.w * (curCoord - prevCoord))
+                ? 1
+                : -1;
+        float prevDist = prevCoord - curSide * prev.w;
+        float curDist = curCoord - curSide * cur.w;
+        // Calculate interpolation weight k and the nudge it inside clipping
+        // boundary with nextafter. Note that since we were previously inside
+        // and now crossing outside, we have to flip the nudge direction for
+        // the weight towards 0 instead of 1.
+        float k = prevDist / (prevDist - curDist);
+        Point3D clipped = prev + (cur - prev) * k;
+        if (curSide * clipped.select(AXIS) > clipped.w) {
+          k = nextafterf(k, 0.0f);
+          clipped = prev + (cur - prev) * k;
+        }
+        outP[numClip] = clipped;
+        outInterp[numClip] = prevInterp + (curInterp - prevInterp) * k;
+        numClip++;
+      }
+    }
+    if (!curMask) {
+      // The current end point is inside the plane, so output point unmodified.
+      if (numClip >= nump + 2) {
+        assert(false);
+        return 0;
+      }
+      outP[numClip] = cur;
+      outInterp[numClip] = curInterp;
+      numClip++;
+    }
+    prev = cur;
+    prevInterp = curInterp;
+    prevCoord = curCoord;
+    prevMask = curMask;
+  }
+  return numClip;
+}
+
+// Helper function to dispatch to perspective span drawing with points that
+// have already been transformed and clipped.
+static inline void draw_perspective_clipped(int nump, Point3D* p_clip,
+                                            Interpolants* interp_clip,
+                                            Texture& colortex, int layer,
+                                            Texture& depthtex) {
+  // If polygon is ouside clip rect, nothing to draw.
+  ClipRect clipRect(colortex);
+  if (!clipRect.overlaps(nump, p_clip)) {
+    return;
+  }
+
+  // Finally draw perspective-correct spans for the polygon.
+  if (colortex.internal_format == GL_RGBA8) {
+    draw_perspective_spans<uint32_t>(nump, p_clip, interp_clip, colortex, layer,
+                                     depthtex, clipRect);
+  } else if (colortex.internal_format == GL_R8) {
+    draw_perspective_spans<uint8_t>(nump, p_clip, interp_clip, colortex, layer,
+                                    depthtex, clipRect);
+  } else {
+    assert(false);
+  }
+}
+
+// Draws a perspective-correct 3D primitive with varying Z value, as opposed
+// to a simple 2D planar primitive with a constant Z value that could be
+// trivially Z rejected. This requires clipping the primitive against the near
+// and far planes to ensure it stays within the valid Z-buffer range. The Z
+// and W of each fragment of the primitives are interpolated across the
+// generated spans and then depth-tested as appropriate.
+// Additionally, vertex attributes must be interpolated with perspective-
+// correction by dividing by W before interpolation, and then later multiplied
+// by W again to produce the final correct attribute value for each fragment.
+// This process is expensive and should be avoided if possible for primitive
+// batches that are known ahead of time to not need perspective-correction.
+static void draw_perspective(int nump, Interpolants interp_outs[4],
+                             Texture& colortex, int layer, Texture& depthtex) {
+  // Lines are not supported with perspective.
+  assert(nump >= 3);
+  // Convert output of vertex shader to screen space.
+  vec4 pos = vertex_shader->gl_Position;
+  vec3_scalar scale =
+      vec3_scalar(ctx->viewport.width(), ctx->viewport.height(), 1) * 0.5f;
+  vec3_scalar offset =
+      make_vec3(make_vec2(ctx->viewport.origin() - colortex.offset), 0.0f) +
+      scale;
+  if (test_none(pos.z <= -pos.w || pos.z >= pos.w)) {
+    // No points cross the near or far planes, so no clipping required.
+    // Just divide coords by W and convert to viewport. We assume the W
+    // coordinate is non-zero and the reciprocal is finite since it would
+    // otherwise fail the test_none condition.
+    Float w = 1.0f / pos.w;
+    vec3 screen = pos.sel(X, Y, Z) * w * scale + offset;
+    Point3D p[4] = {{screen.x.x, screen.y.x, screen.z.x, w.x},
+                    {screen.x.y, screen.y.y, screen.z.y, w.y},
+                    {screen.x.z, screen.y.z, screen.z.z, w.z},
+                    {screen.x.w, screen.y.w, screen.z.w, w.w}};
+    draw_perspective_clipped(nump, p, interp_outs, colortex, layer, depthtex);
+  } else {
+    // Points cross the near or far planes, so we need to clip.
+    // Start with the original 3 or 4 points...
+    Point3D p[4] = {{pos.x.x, pos.y.x, pos.z.x, pos.w.x},
+                    {pos.x.y, pos.y.y, pos.z.y, pos.w.y},
+                    {pos.x.z, pos.y.z, pos.z.z, pos.w.z},
+                    {pos.x.w, pos.y.w, pos.z.w, pos.w.w}};
+    // Clipping can expand the points by 1 for each of 6 view frustum planes.
+    Point3D p_clip[4 + 6];
+    Interpolants interp_clip[4 + 6];
+    // Clip against near and far Z planes.
+    nump = clip_side<Z>(nump, p, interp_outs, p_clip, interp_clip);
+    // If no points are left inside the view frustum, there's nothing to draw.
+    if (nump < 3) {
+      return;
+    }
+    // After clipping against only the near and far planes, we might still
+    // produce points where W = 0, exactly at the camera plane. OpenGL specifies
+    // that for clip coordinates, points must satisfy:
+    //   -W <= X <= W
+    //   -W <= Y <= W
+    //   -W <= Z <= W
+    // When Z = W = 0, this is trivially satisfied, but when we transform and
+    // divide by W below it will produce a divide by 0. Usually we want to only
+    // clip Z to avoid the extra work of clipping X and Y. We can still project
+    // points that fall outside the view frustum X and Y so long as Z is valid.
+    // The span drawing code will then ensure X and Y are clamped to viewport
+    // boundaries. However, in the Z = W = 0 case, sometimes clipping X and Y,
+    // will push W further inside the view frustum so that it is no longer 0,
+    // allowing us to finally proceed to projecting the points to the screen.
+    for (int i = 0; i < nump; i++) {
+      // Found an invalid W, so need to clip against X and Y...
+      if (p_clip[i].w <= 0.0f) {
+        // Ping-pong p_clip -> p_tmp -> p_clip.
+        Point3D p_tmp[4 + 6];
+        Interpolants interp_tmp[4 + 6];
+        nump = clip_side<X>(nump, p_clip, interp_clip, p_tmp, interp_tmp);
+        if (nump < 3) return;
+        nump = clip_side<Y>(nump, p_tmp, interp_tmp, p_clip, interp_clip);
+        if (nump < 3) return;
+        // After clipping against X and Y planes, there's still points left
+        // to draw, so proceed to trying projection now...
+        break;
+      }
+    }
+    // Divide coords by W and convert to viewport.
+    for (int i = 0; i < nump; i++) {
+      float w = 1.0f / p_clip[i].w;
+      // If the W coord is essentially zero, small enough that division would
+      // result in Inf/NaN, then just set the reciprocal itself to zero so that
+      // the coordinates becomes zeroed out, as the only valid point that
+      // satisfies -W <= X/Y/Z <= W is all zeroes.
+      if (!isfinite(w)) w = 0.0f;
+      p_clip[i] = Point3D(p_clip[i].sel(X, Y, Z) * w * scale + offset, w);
+    }
+    draw_perspective_clipped(nump, p_clip, interp_clip, colortex, layer,
+                             depthtex);
+  }
+}
+
+static void draw_quad(int nump, Texture& colortex, int layer,
+                      Texture& depthtex) {
+  // Run vertex shader once for the primitive's vertices.
+  // Reserve space for 6 sets of interpolants, in case we need to clip against
+  // near and far planes in the perspective case.
+  Interpolants interp_outs[4];
+  swgl_ClipMask = nullptr;
+  vertex_shader->run_primitive((char*)interp_outs, sizeof(Interpolants));
+  vec4 pos = vertex_shader->gl_Position;
+  // Check if any vertex W is different from another. If so, use perspective.
+  if (test_any(pos.w != pos.w.x)) {
+    draw_perspective(nump, interp_outs, colortex, layer, depthtex);
+    return;
+  }
+
+  // Convert output of vertex shader to screen space.
+  // Divide coords by W and convert to viewport.
+  float w = 1.0f / pos.w.x;
+  // If the W coord is essentially zero, small enough that division would
+  // result in Inf/NaN, then just set the reciprocal itself to zero so that
+  // the coordinates becomes zeroed out, as the only valid point that
+  // satisfies -W <= X/Y/Z <= W is all zeroes.
+  if (!isfinite(w)) w = 0.0f;
+  vec2 screen = (pos.sel(X, Y) * w + 1) * 0.5f *
+                    vec2_scalar(ctx->viewport.width(), ctx->viewport.height()) +
+                make_vec2(ctx->viewport.origin() - colortex.offset);
+  Point2D p[4] = {{screen.x.x, screen.y.x},
+                  {screen.x.y, screen.y.y},
+                  {screen.x.z, screen.y.z},
+                  {screen.x.w, screen.y.w}};
+
+  // If quad is ouside clip rect, nothing to draw.
+  ClipRect clipRect(colortex);
+  if (!clipRect.overlaps(nump, p)) {
+    return;
+  }
+
+  // Since the quad is assumed 2D, Z is constant across the quad.
+  float screenZ = (pos.z.x * w + 1) * 0.5f;
+  if (screenZ < 0 || screenZ > 1) {
+    // Z values would cross the near or far plane, so just bail.
+    return;
+  }
+  // Since Z doesn't need to be interpolated, just set the fragment shader's
+  // Z and W values here, once and for all fragment shader invocations.
+  uint16_t z = uint16_t(0xFFFF * screenZ);
+  fragment_shader->gl_FragCoord.z = screenZ;
+  fragment_shader->gl_FragCoord.w = w;
+
+  // If supplied a line, adjust it so that it is a quad at least 1 pixel thick.
+  // Assume that for a line that all 4 SIMD lanes were actually filled with
+  // vertexes 0, 1, 1, 0.
+  if (nump == 2) {
+    // Nudge Y height to span at least 1 pixel by advancing to next pixel
+    // boundary so that we step at least 1 row when drawing spans.
+    if (int(p[0].y + 0.5f) == int(p[1].y + 0.5f)) {
+      p[2].y = 1 + int(p[1].y + 0.5f);
+      p[3].y = p[2].y;
+      // Nudge X width to span at least 1 pixel so that rounded coords fall on
+      // separate pixels.
+      if (int(p[0].x + 0.5f) == int(p[1].x + 0.5f)) {
+        p[1].x += 1.0f;
+        p[2].x += 1.0f;
+      }
+    } else {
+      // If the line already spans at least 1 row, then assume line is vertical
+      // or diagonal and just needs to be dilated horizontally.
+      p[2].x += 1.0f;
+      p[3].x += 1.0f;
+    }
+    // Pretend that it's a quad now...
+    nump = 4;
+  }
+
+  // Finally draw 2D spans for the quad. Currently only supports drawing to
+  // RGBA8 and R8 color buffers.
+  if (colortex.internal_format == GL_RGBA8) {
+    draw_quad_spans<uint32_t>(nump, p, z, interp_outs, colortex, layer,
+                              depthtex, clipRect);
+  } else if (colortex.internal_format == GL_R8) {
+    draw_quad_spans<uint8_t>(nump, p, z, interp_outs, colortex, layer, depthtex,
+                             clipRect);
+  } else {
+    assert(false);
+  }
+}
+
+void VertexArray::validate() {
+  int last_enabled = -1;
+  for (int i = 0; i <= max_attrib; i++) {
+    VertexAttrib& attr = attribs[i];
+    if (attr.enabled) {
+      // VertexArray &v = ctx->vertex_arrays[attr.vertex_array];
+      Buffer& vertex_buf = ctx->buffers[attr.vertex_buffer];
+      attr.buf = vertex_buf.buf;
+      attr.buf_size = vertex_buf.size;
+      // debugf("%d %x %d %d %d %d\n", i, attr.type, attr.size, attr.stride,
+      // attr.offset, attr.divisor);
+      last_enabled = i;
+    }
+  }
+  max_attrib = last_enabled;
+}
+
+template <typename INDEX>
+static inline void draw_elements(GLsizei count, GLsizei instancecount,
+                                 size_t offset, VertexArray& v,
+                                 Texture& colortex, int layer,
+                                 Texture& depthtex) {
+  Buffer& indices_buf = ctx->buffers[v.element_array_buffer_binding];
+  if (!indices_buf.buf || offset >= indices_buf.size) {
+    return;
+  }
+  assert((offset & (sizeof(INDEX) - 1)) == 0);
+  INDEX* indices = (INDEX*)(indices_buf.buf + offset);
+  count = min(count, (GLsizei)((indices_buf.size - offset) / sizeof(INDEX)));
+  // Triangles must be indexed at offsets 0, 1, 2.
+  // Quads must be successive triangles indexed at offsets 0, 1, 2, 2, 1, 3.
+  if (count == 6 && indices[1] == indices[0] + 1 &&
+      indices[2] == indices[0] + 2 && indices[5] == indices[0] + 3) {
+    assert(indices[3] == indices[0] + 2 && indices[4] == indices[0] + 1);
+    // Fast path - since there is only a single quad, we only load per-vertex
+    // attribs once for all instances, as they won't change across instances
+    // or within an instance.
+    vertex_shader->load_attribs(v.attribs, indices[0], 0, 4);
+    draw_quad(4, colortex, layer, depthtex);
+    for (GLsizei instance = 1; instance < instancecount; instance++) {
+      vertex_shader->load_attribs(v.attribs, indices[0], instance, 0);
+      draw_quad(4, colortex, layer, depthtex);
+    }
+  } else {
+    for (GLsizei instance = 0; instance < instancecount; instance++) {
+      for (GLsizei i = 0; i + 3 <= count; i += 3) {
+        if (indices[i + 1] != indices[i] + 1 ||
+            indices[i + 2] != indices[i] + 2) {
+          continue;
+        }
+        if (i + 6 <= count && indices[i + 5] == indices[i] + 3) {
+          assert(indices[i + 3] == indices[i] + 2 &&
+                 indices[i + 4] == indices[i] + 1);
+          vertex_shader->load_attribs(v.attribs, indices[i], instance, 4);
+          draw_quad(4, colortex, layer, depthtex);
+          i += 3;
+        } else {
+          vertex_shader->load_attribs(v.attribs, indices[i], instance, 3);
+          draw_quad(3, colortex, layer, depthtex);
+        }
+      }
+    }
+  }
+}
+
+extern "C" {
+
+void DrawElementsInstanced(GLenum mode, GLsizei count, GLenum type,
+                           GLintptr offset, GLsizei instancecount) {
+  if (offset < 0 || count <= 0 || instancecount <= 0 || !vertex_shader ||
+      !fragment_shader) {
+    return;
+  }
+
+  Framebuffer& fb = *get_framebuffer(GL_DRAW_FRAMEBUFFER);
+  Texture& colortex = ctx->textures[fb.color_attachment];
+  if (!colortex.buf) {
+    return;
+  }
+  assert(!colortex.locked);
+  assert(colortex.internal_format == GL_RGBA8 ||
+         colortex.internal_format == GL_R8);
+  Texture& depthtex = ctx->textures[ctx->depthtest ? fb.depth_attachment : 0];
+  if (depthtex.buf) {
+    assert(depthtex.internal_format == GL_DEPTH_COMPONENT16);
+    assert(colortex.width == depthtex.width &&
+           colortex.height == depthtex.height);
+    assert(colortex.offset == depthtex.offset);
+  }
+
+  // debugf("current_vertex_array %d\n", ctx->current_vertex_array);
+  // debugf("indices size: %d\n", indices_buf.size);
+  VertexArray& v = ctx->vertex_arrays[ctx->current_vertex_array];
+  if (ctx->validate_vertex_array) {
+    ctx->validate_vertex_array = false;
+    v.validate();
+  }
+
+#ifdef PRINT_TIMINGS
+  uint64_t start = get_time_value();
+#endif
+
+  ctx->shaded_rows = 0;
+  ctx->shaded_pixels = 0;
+
+  vertex_shader->init_batch();
+
+  switch (type) {
+    case GL_UNSIGNED_SHORT:
+      assert(mode == GL_TRIANGLES);
+      draw_elements<uint16_t>(count, instancecount, offset, v, colortex,
+                              fb.layer, depthtex);
+      break;
+    case GL_UNSIGNED_INT:
+      assert(mode == GL_TRIANGLES);
+      draw_elements<uint32_t>(count, instancecount, offset, v, colortex,
+                              fb.layer, depthtex);
+      break;
+    case GL_NONE:
+      // Non-standard GL extension - if element type is GL_NONE, then we don't
+      // use any element buffer and behave as if DrawArrays was called instead.
+      for (GLsizei instance = 0; instance < instancecount; instance++) {
+        switch (mode) {
+          case GL_LINES:
+            for (GLsizei i = 0; i + 2 <= count; i += 2) {
+              vertex_shader->load_attribs(v.attribs, offset + i, instance, 2);
+              draw_quad(2, colortex, fb.layer, depthtex);
+            }
+            break;
+          case GL_TRIANGLES:
+            for (GLsizei i = 0; i + 3 <= count; i += 3) {
+              vertex_shader->load_attribs(v.attribs, offset + i, instance, 3);
+              draw_quad(3, colortex, fb.layer, depthtex);
+            }
+            break;
+          default:
+            assert(false);
+            break;
+        }
+      }
+      break;
+    default:
+      assert(false);
+      break;
+  }
+
+  if (ctx->samples_passed_query) {
+    Query& q = ctx->queries[ctx->samples_passed_query];
+    q.value += ctx->shaded_pixels;
+  }
+
+#ifdef PRINT_TIMINGS
+  uint64_t end = get_time_value();
+  printf(
+      "%7.3fms draw(%s, %d): %d pixels in %d rows (avg %f pixels/row, "
+      "%fns/pixel)\n",
+      double(end - start) / (1000. * 1000.),
+      ctx->programs[ctx->current_program].impl->get_name(), instancecount,
+      ctx->shaded_pixels, ctx->shaded_rows,
+      double(ctx->shaded_pixels) / ctx->shaded_rows,
+      double(end - start) / max(ctx->shaded_pixels, 1));
+#endif
+}
+
+void Finish() {
+#ifdef PRINT_TIMINGS
+  printf("Finish\n");
+#endif
+}
+
+void MakeCurrent(Context* c) {
+  if (ctx == c) {
+    return;
+  }
+  ctx = c;
+  setup_program(ctx ? ctx->current_program : 0);
+}
+
+Context* CreateContext() { return new Context; }
+
+void ReferenceContext(Context* c) {
+  if (!c) {
+    return;
+  }
+  ++c->references;
+}
+
+void DestroyContext(Context* c) {
+  if (!c) {
+    return;
+  }
+  assert(c->references > 0);
+  --c->references;
+  if (c->references > 0) {
+    return;
+  }
+  if (ctx == c) {
+    MakeCurrent(nullptr);
+  }
+  delete c;
+}
+
+}  // extern "C"