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-rw-r--r--src/shaders/dithering.c527
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diff --git a/src/shaders/dithering.c b/src/shaders/dithering.c
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+++ b/src/shaders/dithering.c
@@ -0,0 +1,527 @@
+/*
+ * This file is part of libplacebo.
+ *
+ * libplacebo is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * libplacebo is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with libplacebo. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <math.h>
+#include "shaders.h"
+
+#include <libplacebo/shaders/dithering.h>
+
+const struct pl_dither_params pl_dither_default_params = { PL_DITHER_DEFAULTS };
+
+struct sh_dither_obj {
+ pl_shader_obj lut;
+};
+
+static void sh_dither_uninit(pl_gpu gpu, void *ptr)
+{
+ struct sh_dither_obj *obj = ptr;
+ pl_shader_obj_destroy(&obj->lut);
+ *obj = (struct sh_dither_obj) {0};
+}
+
+static void fill_dither_matrix(void *data, const struct sh_lut_params *params)
+{
+ pl_assert(params->width > 0 && params->height > 0 && params->comps == 1);
+
+ const struct pl_dither_params *dpar = params->priv;
+ switch (dpar->method) {
+ case PL_DITHER_ORDERED_LUT:
+ pl_assert(params->width == params->height);
+ pl_generate_bayer_matrix(data, params->width);
+ return;
+
+ case PL_DITHER_BLUE_NOISE:
+ pl_assert(params->width == params->height);
+ pl_generate_blue_noise(data, params->width);
+ return;
+
+ case PL_DITHER_ORDERED_FIXED:
+ case PL_DITHER_WHITE_NOISE:
+ case PL_DITHER_METHOD_COUNT:
+ return;
+ }
+
+ pl_unreachable();
+}
+
+static bool dither_method_is_lut(enum pl_dither_method method)
+{
+ switch (method) {
+ case PL_DITHER_BLUE_NOISE:
+ case PL_DITHER_ORDERED_LUT:
+ return true;
+ case PL_DITHER_ORDERED_FIXED:
+ case PL_DITHER_WHITE_NOISE:
+ return false;
+ case PL_DITHER_METHOD_COUNT:
+ break;
+ }
+
+ pl_unreachable();
+}
+
+static inline float approx_gamma(enum pl_color_transfer trc)
+{
+ switch (trc) {
+ case PL_COLOR_TRC_UNKNOWN: return 1.0f;
+ case PL_COLOR_TRC_LINEAR: return 1.0f;
+ case PL_COLOR_TRC_PRO_PHOTO:return 1.8f;
+ case PL_COLOR_TRC_GAMMA18: return 1.8f;
+ case PL_COLOR_TRC_GAMMA20: return 2.0f;
+ case PL_COLOR_TRC_GAMMA24: return 2.4f;
+ case PL_COLOR_TRC_GAMMA26: return 2.6f;
+ case PL_COLOR_TRC_ST428: return 2.6f;
+ case PL_COLOR_TRC_GAMMA28: return 2.8f;
+
+ case PL_COLOR_TRC_SRGB:
+ case PL_COLOR_TRC_BT_1886:
+ case PL_COLOR_TRC_GAMMA22:
+ return 2.2f;
+
+ case PL_COLOR_TRC_PQ:
+ case PL_COLOR_TRC_HLG:
+ case PL_COLOR_TRC_V_LOG:
+ case PL_COLOR_TRC_S_LOG1:
+ case PL_COLOR_TRC_S_LOG2:
+ return 2.0f; // TODO: handle this better
+
+ case PL_COLOR_TRC_COUNT: break;
+ }
+
+ pl_unreachable();
+}
+
+void pl_shader_dither(pl_shader sh, int new_depth,
+ pl_shader_obj *dither_state,
+ const struct pl_dither_params *params)
+{
+ if (!sh_require(sh, PL_SHADER_SIG_COLOR, 0, 0))
+ return;
+
+ if (new_depth <= 0 || new_depth > 256) {
+ PL_WARN(sh, "Invalid dither depth: %d.. ignoring", new_depth);
+ return;
+ }
+
+ sh_describef(sh, "dithering (%d bits)", new_depth);
+ GLSL("// pl_shader_dither \n"
+ "{ \n"
+ "float bias; \n");
+
+ params = PL_DEF(params, &pl_dither_default_params);
+ if (params->lut_size < 0 || params->lut_size > 8) {
+ SH_FAIL(sh, "Invalid `lut_size` specified: %d", params->lut_size);
+ return;
+ }
+
+ enum pl_dither_method method = params->method;
+ ident_t lut = NULL_IDENT;
+ int lut_size = 0;
+
+ if (dither_method_is_lut(method)) {
+ if (!dither_state) {
+ PL_WARN(sh, "LUT-based dither method specified but no dither state "
+ "object given, falling back to non-LUT based methods.");
+ goto fallback;
+ }
+
+ struct sh_dither_obj *obj;
+ obj = SH_OBJ(sh, dither_state, PL_SHADER_OBJ_DITHER,
+ struct sh_dither_obj, sh_dither_uninit);
+ if (!obj)
+ goto fallback;
+
+ bool cache = method == PL_DITHER_BLUE_NOISE;
+ lut_size = 1 << PL_DEF(params->lut_size, pl_dither_default_params.lut_size);
+ lut = sh_lut(sh, sh_lut_params(
+ .object = &obj->lut,
+ .var_type = PL_VAR_FLOAT,
+ .width = lut_size,
+ .height = lut_size,
+ .comps = 1,
+ .fill = fill_dither_matrix,
+ .signature = (CACHE_KEY_DITHER ^ method) * lut_size,
+ .cache = cache ? SH_CACHE(sh) : NULL,
+ .priv = (void *) params,
+ ));
+ if (!lut)
+ goto fallback;
+ }
+
+ goto done;
+
+fallback:
+ method = PL_DITHER_ORDERED_FIXED;
+ // fall through
+
+done: ;
+
+ int size = 0;
+ if (lut) {
+ size = lut_size;
+ } else if (method == PL_DITHER_ORDERED_FIXED) {
+ size = 16; // hard-coded size
+ }
+
+ if (size) {
+ // Transform the screen position to the cyclic range [0,1)
+ GLSL("vec2 pos = fract(gl_FragCoord.xy * 1.0/"$"); \n", SH_FLOAT(size));
+
+ if (params->temporal) {
+ int phase = SH_PARAMS(sh).index % 8;
+ float r = phase * (M_PI / 2); // rotate
+ float m = phase < 4 ? 1 : -1; // mirror
+ float mat[2][2] = {
+ {cos(r), -sin(r) },
+ {sin(r) * m, cos(r) * m},
+ };
+
+ ident_t rot = sh_var(sh, (struct pl_shader_var) {
+ .var = pl_var_mat2("dither_rot"),
+ .data = &mat[0][0],
+ .dynamic = true,
+ });
+ GLSL("pos = fract("$" * pos + vec2(1.0));\n", rot);
+ }
+ }
+
+ switch (method) {
+ case PL_DITHER_WHITE_NOISE: {
+ ident_t prng = sh_prng(sh, params->temporal, NULL);
+ GLSL("bias = "$".x;\n", prng);
+ break;
+ }
+
+ case PL_DITHER_ORDERED_FIXED:
+ // Bitwise ordered dither using only 32-bit uints
+ GLSL("uvec2 xy = uvec2(pos * 16.0) %% 16u; \n"
+ // Bitwise merge (morton number)
+ "xy.x = xy.x ^ xy.y; \n"
+ "xy = (xy | xy << 2) & uvec2(0x33333333); \n"
+ "xy = (xy | xy << 1) & uvec2(0x55555555); \n"
+ // Bitwise inversion
+ "uint b = xy.x + (xy.y << 1); \n"
+ "b = (b * 0x0802u & 0x22110u) | \n"
+ " (b * 0x8020u & 0x88440u); \n"
+ "b = 0x10101u * b; \n"
+ "b = (b >> 16) & 0xFFu; \n"
+ // Generate bias value
+ "bias = float(b) * 1.0/256.0; \n");
+ break;
+
+ case PL_DITHER_BLUE_NOISE:
+ case PL_DITHER_ORDERED_LUT:
+ pl_assert(lut);
+ GLSL("bias = "$"(ivec2(pos * "$"));\n", lut, SH_FLOAT(lut_size));
+ break;
+
+ case PL_DITHER_METHOD_COUNT:
+ pl_unreachable();
+ }
+
+ // Scale factor for dither rounding
+ GLSL("const float scale = %llu.0; \n", (1LLU << new_depth) - 1);
+
+ const float gamma = approx_gamma(params->transfer);
+ if (gamma != 1.0f && new_depth <= 4) {
+ GLSL("const float gamma = "$"; \n"
+ "vec4 color_lin = pow(color, vec4(gamma)); \n",
+ SH_FLOAT(gamma));
+
+ if (new_depth == 1) {
+ // Special case for bit depth 1 dithering, in this case we can just
+ // ignore the low/high rounding because we know we are always
+ // dithering between 0.0 and 1.0.
+ GLSL("const vec4 low = vec4(0.0); \n"
+ "const vec4 high = vec4(1.0); \n"
+ "vec4 offset = color_lin; \n");
+ } else {
+ // Linearize the low, high and current color values
+ GLSL("vec4 low = floor(color * scale) / scale; \n"
+ "vec4 high = ceil(color * scale) / scale; \n"
+ "vec4 low_lin = pow(low, vec4(gamma)); \n"
+ "vec4 high_lin = pow(high, vec4(gamma)); \n"
+ "vec4 range = high_lin - low_lin; \n"
+ "vec4 offset = (color_lin - low_lin) / \n"
+ " max(range, 1e-6); \n");
+ }
+
+ // Mix in the correct ratio corresponding to the offset and bias
+ GLSL("color = mix(low, high, greaterThan(offset, vec4(bias))); \n");
+ } else {
+ // Approximate each gamma segment as a straight line, this simplifies
+ // the process of dithering down to a single scale and (biased) round.
+ GLSL("color = scale * color + vec4(bias); \n"
+ "color = floor(color) * (1.0 / scale); \n");
+ }
+
+ GLSL("} \n");
+}
+
+/* Error diffusion code is taken from mpv, original copyright (c) 2019 Bin Jin
+ *
+ * mpv is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * mpv is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with mpv. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+// After a (y, x) -> (y, x + y * shift) mapping, find the right most column that
+// will be affected by the current column.
+static int compute_rightmost_shifted_column(const struct pl_error_diffusion_kernel *k)
+{
+ int ret = 0;
+ for (int y = 0; y <= PL_EDF_MAX_DY; y++) {
+ for (int x = PL_EDF_MIN_DX; x <= PL_EDF_MAX_DX; x++) {
+ if (k->pattern[y][x - PL_EDF_MIN_DX] != 0) {
+ int shifted_x = x + y * k->shift;
+
+ // The shift mapping guarantees current column (or left of it)
+ // won't be affected by error diffusion.
+ assert(shifted_x > 0);
+
+ ret = PL_MAX(ret, shifted_x);
+ }
+ }
+ }
+ return ret;
+}
+
+size_t pl_error_diffusion_shmem_req(const struct pl_error_diffusion_kernel *kernel,
+ int height)
+{
+ // We add PL_EDF_MAX_DY empty lines on the bottom to handle errors
+ // propagated out from bottom side.
+ int rows = height + PL_EDF_MAX_DY;
+ int shifted_columns = compute_rightmost_shifted_column(kernel) + 1;
+
+ // The shared memory is an array of size rows*shifted_columns. Each element
+ // is a single uint for three RGB component.
+ return rows * shifted_columns * sizeof(uint32_t);
+}
+
+bool pl_shader_error_diffusion(pl_shader sh, const struct pl_error_diffusion_params *params)
+{
+ const int width = params->input_tex->params.w, height = params->input_tex->params.h;
+ const struct pl_glsl_version glsl = sh_glsl(sh);
+ const struct pl_error_diffusion_kernel *kernel =
+ PL_DEF(params->kernel, &pl_error_diffusion_sierra_lite);
+
+ pl_assert(params->output_tex->params.w == width);
+ pl_assert(params->output_tex->params.h == height);
+ if (!sh_require(sh, PL_SHADER_SIG_NONE, width, height))
+ return false;
+
+ if (params->new_depth <= 0 || params->new_depth > 256) {
+ PL_WARN(sh, "Invalid dither depth: %d.. ignoring", params->new_depth);
+ return false;
+ }
+
+ // The parallel error diffusion works by applying the shift mapping first.
+ // Taking the Floyd and Steinberg algorithm for example. After applying
+ // the (y, x) -> (y, x + y * shift) mapping (with shift=2), all errors are
+ // propagated into the next few columns, which makes parallel processing on
+ // the same column possible.
+ //
+ // X 7/16 X 7/16
+ // 3/16 5/16 1/16 ==> 0 0 3/16 5/16 1/16
+
+ // Figuring out the size of rectangle containing all shifted pixels.
+ // The rectangle height is not changed.
+ int shifted_width = width + (height - 1) * kernel->shift;
+
+ // We process all pixels from the shifted rectangles column by column, with
+ // a single global work group of size |block_size|.
+ // Figuring out how many block are required to process all pixels. We need
+ // this explicitly to make the number of barrier() calls match.
+ int block_size = PL_MIN(glsl.max_group_threads, height);
+ int blocks = PL_DIV_UP(height * shifted_width, block_size);
+
+ // If we figure out how many of the next columns will be affected while the
+ // current columns is being processed. We can store errors of only a few
+ // columns in the shared memory. Using a ring buffer will further save the
+ // cost while iterating to next column.
+ //
+ int ring_buffer_rows = height + PL_EDF_MAX_DY;
+ int ring_buffer_columns = compute_rightmost_shifted_column(kernel) + 1;
+ ident_t ring_buffer_size = sh_const(sh, (struct pl_shader_const) {
+ .type = PL_VAR_UINT,
+ .name = "ring_buffer_size",
+ .data = &(unsigned) { ring_buffer_rows * ring_buffer_columns },
+ .compile_time = true,
+ });
+
+ // Compute shared memory requirements and try enabling compute shader.
+ size_t shmem_req = ring_buffer_rows * ring_buffer_columns * sizeof(uint32_t);
+ if (!sh_try_compute(sh, block_size, 1, false, shmem_req)) {
+ PL_ERR(sh, "Cannot execute error diffusion kernel: too old GPU or "
+ "insufficient compute shader memory!");
+ return false;
+ }
+
+ ident_t in_tex = sh_desc(sh, (struct pl_shader_desc) {
+ .binding.object = params->input_tex,
+ .desc = {
+ .name = "input_tex",
+ .type = PL_DESC_SAMPLED_TEX,
+ },
+ });
+
+ ident_t out_img = sh_desc(sh, (struct pl_shader_desc) {
+ .binding.object = params->output_tex,
+ .desc = {
+ .name = "output_tex",
+ .type = PL_DESC_STORAGE_IMG,
+ .access = PL_DESC_ACCESS_WRITEONLY,
+ },
+ });
+
+ sh->output = PL_SHADER_SIG_NONE;
+ sh_describef(sh, "error diffusion (%s, %d bits)",
+ kernel->name, params->new_depth);
+
+ // Defines the ring buffer in shared memory.
+ GLSLH("shared uint err_rgb8["$"]; \n", ring_buffer_size);
+ GLSL("// pl_shader_error_diffusion \n"
+ // Safeguard against accidental over-execution
+ "if (gl_WorkGroupID != uvec3(0)) \n"
+ " return; \n"
+ // Initialize the ring buffer.
+ "for (uint i = gl_LocalInvocationIndex; i < "$"; i+=gl_WorkGroupSize.x)\n"
+ " err_rgb8[i] = 0u; \n"
+
+ // Main block loop, add barrier here to have previous block all
+ // processed before starting the processing of the next.
+ "for (uint block_id = 0; block_id < "$"; block_id++) { \n"
+ "barrier(); \n"
+ // Compute the coordinate of the pixel we are currently processing,
+ // both before and after the shift mapping.
+ "uint id = block_id * gl_WorkGroupSize.x + gl_LocalInvocationIndex; \n"
+ "const uint height = "$"; \n"
+ "int y = int(id %% height), x_shifted = int(id / height); \n"
+ "int x = x_shifted - y * %d; \n"
+ // Proceed only if we are processing a valid pixel.
+ "if (x >= 0 && x < "$") { \n"
+ // The index that the current pixel have on the ring buffer.
+ "uint idx = uint(x_shifted * "$" + y) %% "$"; \n"
+ // Fetch the current pixel.
+ "vec4 pix_orig = texelFetch("$", ivec2(x, y), 0); \n"
+ "vec3 pix = pix_orig.rgb; \n",
+ ring_buffer_size,
+ SH_UINT(blocks),
+ SH_UINT(height),
+ kernel->shift,
+ SH_INT(width),
+ SH_INT(ring_buffer_rows),
+ ring_buffer_size,
+ in_tex);
+
+ // The dithering will quantize pixel value into multiples of 1/dither_quant.
+ int dither_quant = (1 << params->new_depth) - 1;
+
+ // We encode errors in RGB components into a single 32-bit unsigned integer.
+ // The error we propagate from the current pixel is in range of
+ // [-0.5 / dither_quant, 0.5 / dither_quant]. While not quite obvious, the
+ // sum of all errors been propagated into a pixel is also in the same range.
+ // It's possible to map errors in this range into [-127, 127], and use an
+ // unsigned 8-bit integer to store it (using standard two's complement).
+ // The three 8-bit unsigned integers can then be encoded into a single
+ // 32-bit unsigned integer, with two 4-bit padding to prevent addition
+ // operation overflows affecting other component. There are at most 12
+ // addition operations on each pixel, so 4-bit padding should be enough.
+ // The overflow from R component will be discarded.
+ //
+ // The following figure is how the encoding looks like.
+ //
+ // +------------------------------------+
+ // |RRRRRRRR|0000|GGGGGGGG|0000|BBBBBBBB|
+ // +------------------------------------+
+ //
+
+ // The bitshift position for R and G component.
+ const int bitshift_r = 24, bitshift_g = 12;
+ // The multiplier we use to map [-0.5, 0.5] to [-127, 127].
+ const int uint8_mul = 127 * 2;
+
+ GLSL(// Add the error previously propagated into current pixel, and clear
+ // it in the ring buffer.
+ "uint err_u32 = err_rgb8[idx] + %uu; \n"
+ "pix = pix * %d.0 + vec3(int((err_u32 >> %d) & 0xFFu) - 128, \n"
+ " int((err_u32 >> %d) & 0xFFu) - 128, \n"
+ " int( err_u32 & 0xFFu) - 128) / %d.0; \n"
+ "err_rgb8[idx] = 0u; \n"
+ // Write the dithered pixel.
+ "vec3 dithered = round(pix); \n"
+ "imageStore("$", ivec2(x, y), vec4(dithered / %d.0, pix_orig.a)); \n"
+ // Prepare for error propagation pass
+ "vec3 err_divided = (pix - dithered) * %d.0 / %d.0; \n"
+ "ivec3 tmp; \n",
+ (128u << bitshift_r) | (128u << bitshift_g) | 128u,
+ dither_quant, bitshift_r, bitshift_g, uint8_mul,
+ out_img, dither_quant,
+ uint8_mul, kernel->divisor);
+
+ // Group error propagation with same weight factor together, in order to
+ // reduce the number of annoying error encoding.
+ for (int dividend = 1; dividend <= kernel->divisor; dividend++) {
+ bool err_assigned = false;
+
+ for (int y = 0; y <= PL_EDF_MAX_DY; y++) {
+ for (int x = PL_EDF_MIN_DX; x <= PL_EDF_MAX_DX; x++) {
+ if (kernel->pattern[y][x - PL_EDF_MIN_DX] != dividend)
+ continue;
+
+ if (!err_assigned) {
+ err_assigned = true;
+
+ GLSL("tmp = ivec3(round(err_divided * %d.0)); \n"
+ "err_u32 = (uint(tmp.r & 0xFF) << %d) | \n"
+ " (uint(tmp.g & 0xFF) << %d) | \n"
+ " uint(tmp.b & 0xFF); \n",
+ dividend,
+ bitshift_r, bitshift_g);
+ }
+
+ int shifted_x = x + y * kernel->shift;
+
+ // Unlike the right border, errors propagated out from left
+ // border will remain in the ring buffer. This will produce
+ // visible artifacts near the left border, especially for
+ // shift=3 kernels.
+ if (x < 0)
+ GLSL("if (x >= %d) \n", -x);
+
+ // Calculate the new position in the ring buffer to propagate
+ // the error into.
+ int ring_buffer_delta = shifted_x * ring_buffer_rows + y;
+ GLSL("atomicAdd(err_rgb8[(idx + %du) %% "$"], err_u32); \n",
+ ring_buffer_delta, ring_buffer_size);
+ }
+ }
+ }
+
+ GLSL("}} \n"); // end of main loop + valid pixel conditional
+ return true;
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-01 12:52:47 +0000