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diff --git a/dom/canvas/DrawTargetWebglInternal.h b/dom/canvas/DrawTargetWebglInternal.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef _MOZILLA_GFX_DRAWTARGETWEBGL_INTERNAL_H
+#define _MOZILLA_GFX_DRAWTARGETWEBGL_INTERNAL_H
+
+#include "DrawTargetWebgl.h"
+
+#include "mozilla/HashFunctions.h"
+#include "mozilla/gfx/PathSkia.h"
+#include "mozilla/gfx/WPFGpuRaster.h"
+
+namespace mozilla::gfx {
+
+// TexturePacker implements a bin-packing algorithm for 2D rectangles. It uses
+// a binary tree that partitions the space of a node at a given split. This
+// produces two children, one on either side of the split. This subdivision
+// proceeds recursively as necessary.
+class TexturePacker {
+ public:
+  explicit TexturePacker(const IntRect& aBounds, bool aAvailable = true)
+      : mBounds(aBounds),
+        mAvailable(aAvailable ? std::min(aBounds.width, aBounds.height) : 0) {}
+
+  Maybe<IntPoint> Insert(const IntSize& aSize);
+
+  bool Remove(const IntRect& aBounds);
+
+  const IntRect& GetBounds() const { return mBounds; }
+
+ private:
+  bool IsLeaf() const { return !mChildren; }
+  bool IsFullyAvailable() const { return IsLeaf() && mAvailable > 0; }
+
+  void DiscardChildren() { mChildren.reset(); }
+
+  // If applicable, the two children produced by picking a single axis split
+  // within the node's bounds and subdividing the bounds there.
+  UniquePtr<TexturePacker[]> mChildren;
+  // The bounds enclosing this node and any children within it.
+  IntRect mBounds;
+  // For a leaf node, specifies the size of the smallest dimension available to
+  // allocate. For a branch node, specifies largest potential available size of
+  // all children. This can be used during the allocation process to rapidly
+  // reject certain sub-trees without having to search all the way to a leaf
+  // node if we know that largest available size within the sub-tree wouldn't
+  // fit the requested size.
+  int mAvailable = 0;
+};
+
+// CacheEnty is a generic interface for various items that need to be cached to
+// a texture.
+class CacheEntry : public RefCounted<CacheEntry> {
+ public:
+  MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(CacheEntry)
+
+  CacheEntry(const Matrix& aTransform, const IntRect& aBounds, HashNumber aHash)
+      : mTransform(aTransform), mBounds(aBounds), mHash(aHash) {}
+  virtual ~CacheEntry() = default;
+
+  void Link(const RefPtr<TextureHandle>& aHandle);
+  void Unlink();
+
+  const RefPtr<TextureHandle>& GetHandle() const { return mHandle; }
+
+  const Matrix& GetTransform() const { return mTransform; }
+  const IntRect& GetBounds() const { return mBounds; }
+  HashNumber GetHash() const { return mHash; }
+
+  virtual bool IsValid() const { return true; }
+
+ protected:
+  virtual void RemoveFromList() = 0;
+
+  // The handle of the rendered cache item.
+  RefPtr<TextureHandle> mHandle;
+  // The transform that was used to render the entry. This is necessary as
+  // the geometry might only be correctly rendered in device space after
+  // the transform is applied, so in general we can't cache untransformed
+  // geometry.
+  Matrix mTransform;
+  // The device space bounds of the rendered geometry.
+  IntRect mBounds;
+  // A hash of the geometry that may be used for quickly rejecting entries.
+  HashNumber mHash;
+};
+
+// CacheEntryImpl provides type-dependent boilerplate code for implementations
+// of CacheEntry.
+template <typename T>
+class CacheEntryImpl : public CacheEntry, public LinkedListElement<RefPtr<T>> {
+  typedef LinkedListElement<RefPtr<T>> ListType;
+
+ public:
+  CacheEntryImpl(const Matrix& aTransform, const IntRect& aBounds,
+                 HashNumber aHash)
+      : CacheEntry(aTransform, aBounds, aHash) {}
+
+  void RemoveFromList() override {
+    if (ListType::isInList()) {
+      ListType::remove();
+    }
+  }
+};
+
+// CacheImpl manages a list of CacheEntry.
+template <typename T, bool BIG>
+class CacheImpl {
+ protected:
+  typedef LinkedList<RefPtr<T>> ListType;
+
+  // Whether the cache should be small and space-efficient or prioritize speed.
+  static constexpr size_t kNumChains = BIG ? 499 : 17;
+
+ public:
+  ~CacheImpl() {
+    for (auto& chain : mChains) {
+      while (RefPtr<T> entry = chain.popLast()) {
+        entry->Unlink();
+      }
+    }
+  }
+
+ protected:
+  ListType& GetChain(HashNumber aHash) { return mChains[aHash % kNumChains]; }
+
+  void Insert(T* aEntry) { GetChain(aEntry->GetHash()).insertFront(aEntry); }
+
+  ListType mChains[kNumChains];
+};
+
+// TextureHandle is an abstract base class for supplying textures to drawing
+// commands that may be backed by different resource types (such as a shared
+// or standalone texture). It may be further linked to use-specific metadata
+// such as for shadow drawing or for cached entries in the glyph cache.
+class TextureHandle : public RefCounted<TextureHandle>,
+                      public LinkedListElement<RefPtr<TextureHandle>> {
+ public:
+  MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(TextureHandle)
+
+  enum Type { SHARED, STANDALONE };
+
+  virtual Type GetType() const = 0;
+  virtual const RefPtr<WebGLTextureJS>& GetWebGLTexture() const = 0;
+  virtual IntRect GetBounds() const = 0;
+  IntSize GetSize() const { return GetBounds().Size(); }
+  virtual IntSize GetBackingSize() const = 0;
+  virtual SurfaceFormat GetFormat() const = 0;
+  virtual size_t UsedBytes() const = 0;
+
+  static inline size_t UsedBytes(SurfaceFormat aFormat, const IntSize& aSize) {
+    return size_t(BytesPerPixel(aFormat)) * size_t(aSize.width) *
+           size_t(aSize.height);
+  }
+
+  virtual void UpdateSize(const IntSize& aSize) {}
+
+  virtual void Cleanup(DrawTargetWebgl::SharedContext& aContext) {}
+
+  virtual ~TextureHandle() {}
+
+  bool IsValid() const { return mValid; }
+  void Invalidate() { mValid = false; }
+
+  void SetSurface(SourceSurface* aSurface) { mSurface = aSurface; }
+  SourceSurface* GetSurface() const { return mSurface; }
+
+  float GetSigma() const { return mSigma; }
+  void SetSigma(float aSigma) { mSigma = aSigma; }
+  bool IsShadow() const { return mSigma >= 0.0f; }
+
+  void SetSamplingOffset(const IntPoint& aSamplingOffset) {
+    mSamplingOffset = aSamplingOffset;
+  }
+  const IntPoint& GetSamplingOffset() const { return mSamplingOffset; }
+  IntRect GetSamplingRect() const {
+    return IntRect(GetSamplingOffset(), GetSize());
+  }
+
+  const RefPtr<CacheEntry>& GetCacheEntry() const { return mCacheEntry; }
+  void SetCacheEntry(const RefPtr<CacheEntry>& aEntry) { mCacheEntry = aEntry; }
+
+  // Note as used if there is corresponding surface or cache entry.
+  bool IsUsed() const {
+    return mSurface || (mCacheEntry && mCacheEntry->IsValid());
+  }
+
+ private:
+  bool mValid = true;
+  // If applicable, weak pointer to the SourceSurface that is linked to this
+  // TextureHandle.
+  SourceSurface* mSurface = nullptr;
+  // If this TextureHandle stores a cached shadow, then we need to remember the
+  // blur sigma used to produce the shadow.
+  float mSigma = -1.0f;
+  // If the originating surface requested a sampling rect, then we need to know
+  // the offset of the subrect within the surface for texture coordinates.
+  IntPoint mSamplingOffset;
+  // If applicable, the CacheEntry that is linked to this TextureHandle.
+  RefPtr<CacheEntry> mCacheEntry;
+};
+
+class SharedTextureHandle;
+
+// SharedTexture is a large slab texture that is subdivided (by using a
+// TexturePacker) to hold many small SharedTextureHandles. This avoids needing
+// to allocate many WebGL textures for every single small Canvas 2D texture.
+class SharedTexture : public RefCounted<SharedTexture> {
+ public:
+  MOZ_DECLARE_REFCOUNTED_TYPENAME(SharedTexture)
+
+  SharedTexture(const IntSize& aSize, SurfaceFormat aFormat,
+                const RefPtr<WebGLTextureJS>& aTexture);
+
+  already_AddRefed<SharedTextureHandle> Allocate(const IntSize& aSize);
+  bool Free(const SharedTextureHandle& aHandle);
+
+  SurfaceFormat GetFormat() const { return mFormat; }
+  IntSize GetSize() const { return mPacker.GetBounds().Size(); }
+
+  size_t UsedBytes() const {
+    return TextureHandle::UsedBytes(GetFormat(), GetSize());
+  }
+
+  bool HasAllocatedHandles() const { return mAllocatedHandles > 0; }
+
+  const RefPtr<WebGLTextureJS>& GetWebGLTexture() const { return mTexture; }
+
+ private:
+  TexturePacker mPacker;
+  SurfaceFormat mFormat;
+  RefPtr<WebGLTextureJS> mTexture;
+  size_t mAllocatedHandles = 0;
+};
+
+// SharedTextureHandle is an allocated region within a large SharedTexture page
+// that owns it.
+class SharedTextureHandle : public TextureHandle {
+  friend class SharedTexture;
+
+ public:
+  MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(SharedTextureHandle, override)
+
+  SharedTextureHandle(const IntRect& aBounds, SharedTexture* aTexture);
+
+  Type GetType() const override { return Type::SHARED; }
+
+  const RefPtr<WebGLTextureJS>& GetWebGLTexture() const override {
+    return mTexture->GetWebGLTexture();
+  }
+
+  IntRect GetBounds() const override { return mBounds; }
+  IntSize GetBackingSize() const override { return mTexture->GetSize(); }
+
+  SurfaceFormat GetFormat() const override { return mTexture->GetFormat(); }
+
+  size_t UsedBytes() const override {
+    return TextureHandle::UsedBytes(GetFormat(), mBounds.Size());
+  }
+
+  void Cleanup(DrawTargetWebgl::SharedContext& aContext) override;
+
+  const RefPtr<SharedTexture>& GetOwner() const { return mTexture; }
+
+ private:
+  IntRect mBounds;
+  RefPtr<SharedTexture> mTexture;
+};
+
+// StandaloneTexture is a texture that can not be effectively shared within
+// a SharedTexture page, such that it is better to assign it its own WebGL
+// texture.
+class StandaloneTexture : public TextureHandle {
+ public:
+  MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(StandaloneTexture, override)
+
+  StandaloneTexture(const IntSize& aSize, SurfaceFormat aFormat,
+                    const RefPtr<WebGLTextureJS>& aTexture);
+
+  Type GetType() const override { return Type::STANDALONE; }
+
+  SurfaceFormat GetFormat() const override { return mFormat; }
+
+  const RefPtr<WebGLTextureJS>& GetWebGLTexture() const override {
+    return mTexture;
+  }
+
+  IntRect GetBounds() const override { return IntRect(IntPoint(0, 0), mSize); }
+  IntSize GetBackingSize() const override { return mSize; }
+
+  size_t UsedBytes() const override {
+    return TextureHandle::UsedBytes(mFormat, mSize);
+  }
+
+  void UpdateSize(const IntSize& aSize) override { mSize = aSize; }
+
+  void Cleanup(DrawTargetWebgl::SharedContext& aContext) override;
+
+ private:
+  IntSize mSize;
+  SurfaceFormat mFormat;
+  RefPtr<WebGLTextureJS> mTexture;
+};
+
+// GlyphCacheEntry stores rendering metadata for a rendered text run, as well
+// the handle to the texture it was rendered into, so that it can be located
+// for reuse under similar rendering circumstances.
+class GlyphCacheEntry : public CacheEntryImpl<GlyphCacheEntry> {
+ public:
+  MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(GlyphCacheEntry, override)
+
+  GlyphCacheEntry(const GlyphBuffer& aBuffer, const DeviceColor& aColor,
+                  const Matrix& aTransform, const IntPoint& aQuantizeScale,
+                  const IntRect& aBounds, const IntRect& aFullBounds,
+                  HashNumber aHash,
+                  StoredStrokeOptions* aStrokeOptions = nullptr);
+  ~GlyphCacheEntry();
+
+  const GlyphBuffer& GetGlyphBuffer() const { return mBuffer; }
+
+  bool MatchesGlyphs(const GlyphBuffer& aBuffer, const DeviceColor& aColor,
+                     const Matrix& aTransform, const IntPoint& aQuantizeOffset,
+                     const IntPoint& aBoundsOffset, const IntRect& aClipRect,
+                     HashNumber aHash, const StrokeOptions* aStrokeOptions);
+
+  static HashNumber HashGlyphs(const GlyphBuffer& aBuffer,
+                               const Matrix& aTransform,
+                               const IntPoint& aQuantizeScale);
+
+ private:
+  // The glyph keys used to render the text run.
+  GlyphBuffer mBuffer = {nullptr, 0};
+  // The color of the text run.
+  DeviceColor mColor;
+  // The full bounds of the text run without any clipping applied.
+  IntRect mFullBounds;
+  // Stroke options for the text run.
+  UniquePtr<StoredStrokeOptions> mStrokeOptions;
+};
+
+// GlyphCache maintains a list of GlyphCacheEntry's representing previously
+// rendered text runs. The cache is searched to see if a given incoming text
+// run has already been rendered to a texture, and if so, just reuses it.
+// Otherwise, the text run will be rendered to a new texture handle and
+// inserted into a new GlyphCacheEntry to represent it.
+class GlyphCache : public LinkedListElement<GlyphCache>,
+                   public CacheImpl<GlyphCacheEntry, false> {
+ public:
+  explicit GlyphCache(ScaledFont* aFont);
+
+  ScaledFont* GetFont() const { return mFont; }
+
+  already_AddRefed<GlyphCacheEntry> FindEntry(const GlyphBuffer& aBuffer,
+                                              const DeviceColor& aColor,
+                                              const Matrix& aTransform,
+                                              const IntPoint& aQuantizeScale,
+                                              const IntRect& aClipRect,
+                                              HashNumber aHash,
+                                              const StrokeOptions* aOptions);
+
+  already_AddRefed<GlyphCacheEntry> InsertEntry(
+      const GlyphBuffer& aBuffer, const DeviceColor& aColor,
+      const Matrix& aTransform, const IntPoint& aQuantizeScale,
+      const IntRect& aBounds, const IntRect& aFullBounds, HashNumber aHash,
+      const StrokeOptions* aOptions);
+
+ private:
+  // Weak pointer to the owning font
+  ScaledFont* mFont;
+};
+
+struct QuantizedPath {
+  explicit QuantizedPath(const WGR::Path& aPath);
+  // Ensure the path can only be moved, but not copied.
+  QuantizedPath(QuantizedPath&&) noexcept;
+  QuantizedPath(const QuantizedPath&) = delete;
+  ~QuantizedPath();
+
+  bool operator==(const QuantizedPath&) const;
+
+  WGR::Path mPath;
+};
+
+struct PathVertexRange {
+  uint32_t mOffset;
+  uint32_t mLength;
+
+  PathVertexRange() : mOffset(0), mLength(0) {}
+  PathVertexRange(uint32_t aOffset, uint32_t aLength)
+      : mOffset(aOffset), mLength(aLength) {}
+
+  bool IsValid() const { return mLength > 0; }
+};
+
+// PathCacheEntry stores a rasterized version of a supplied path with a given
+// pattern.
+class PathCacheEntry : public CacheEntryImpl<PathCacheEntry> {
+ public:
+  MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(PathCacheEntry, override)
+
+  PathCacheEntry(QuantizedPath&& aPath, Pattern* aPattern,
+                 StoredStrokeOptions* aStrokeOptions, const Matrix& aTransform,
+                 const IntRect& aBounds, const Point& aOrigin, HashNumber aHash,
+                 float aSigma = -1.0f);
+
+  bool MatchesPath(const QuantizedPath& aPath, const Pattern* aPattern,
+                   const StrokeOptions* aStrokeOptions,
+                   const Matrix& aTransform, const IntRect& aBounds,
+                   const Point& aOrigin, HashNumber aHash, float aSigma);
+
+  static HashNumber HashPath(const QuantizedPath& aPath,
+                             const Pattern* aPattern, const Matrix& aTransform,
+                             const IntRect& aBounds, const Point& aOrigin);
+
+  const QuantizedPath& GetPath() const { return mPath; }
+
+  const Point& GetOrigin() const { return mOrigin; }
+
+  // Valid if either a mask (no pattern) or there is valid pattern.
+  bool IsValid() const override { return !mPattern || mPattern->IsValid(); }
+
+  const PathVertexRange& GetVertexRange() const { return mVertexRange; }
+  void SetVertexRange(const PathVertexRange& aRange) { mVertexRange = aRange; }
+
+ private:
+  // The actual path geometry supplied
+  QuantizedPath mPath;
+  // The transformed origin of the path
+  Point mOrigin;
+  // The pattern used to rasterize the path, if not a mask
+  UniquePtr<Pattern> mPattern;
+  // The StrokeOptions used for stroked paths, if applicable
+  UniquePtr<StoredStrokeOptions> mStrokeOptions;
+  // The shadow blur sigma
+  float mSigma;
+  // If the path has cached geometry in the vertex buffer.
+  PathVertexRange mVertexRange;
+};
+
+class PathCache : public CacheImpl<PathCacheEntry, true> {
+ public:
+  PathCache() = default;
+
+  already_AddRefed<PathCacheEntry> FindOrInsertEntry(
+      QuantizedPath aPath, const Pattern* aPattern,
+      const StrokeOptions* aStrokeOptions, const Matrix& aTransform,
+      const IntRect& aBounds, const Point& aOrigin, float aSigma = -1.0f);
+
+  void ClearVertexRanges();
+};
+
+}  // namespace mozilla::gfx
+
+#endif  // _MOZILLA_GFX_DRAWTARGETWEBGL_INTERNAL_H