Bug 1167235 - Part 1 - Render canvas2D into TextureClient directly. r=Bas

2016-06-28 14:06:51 +02:00 · 2016-06-28 14:06:51 +02:00 · 9367516d33
--- a/dom/canvas/CanvasRenderingContext2D.cpp
+++ b/dom/canvas/CanvasRenderingContext2D.cpp
@ -85,6 +85,7 @@
 #include "mozilla/EndianUtils.h"
 #include "mozilla/gfx/2D.h"
 #include "mozilla/gfx/Helpers.h"
+#include "mozilla/gfx/Tools.h"
 #include "mozilla/gfx/PathHelpers.h"
 #include "mozilla/gfx/DataSurfaceHelpers.h"
 #include "mozilla/gfx/PatternHelpers.h"
@ -120,6 +121,7 @@
 #include "CanvasUtils.h"
 #include "mozilla/StyleSetHandle.h"
 #include "mozilla/StyleSetHandleInlines.h"
+#include "mozilla/layers/CanvasClient.h"

 #undef free // apparently defined by some windows header, clashing with a free()
            // method in SkTypes.h
@ -223,10 +225,32 @@ protected:
  Point mEnd;
 };

+bool
+CanvasRenderingContext2D::PatternIsOpaque(CanvasRenderingContext2D::Style aStyle) const
+{
+  const ContextState& state = CurrentState();
+  if (state.globalAlpha < 1.0) {
+    return false;
+  }
+
+  if (state.patternStyles[aStyle] && state.patternStyles[aStyle]->mSurface) {
+    return IsOpaqueFormat(state.patternStyles[aStyle]->mSurface->GetFormat());
+  }
+
+  // TODO: for gradient patterns we could check that all stops are opaque
+  // colors.
+
+  if (!state.gradientStyles[aStyle]) {
+    // it's a color pattern.
+    return Color::FromABGR(state.colorStyles[aStyle]).a >= 1.0;
+  }
+
+  return false;
+}
+
 // This class is named 'GeneralCanvasPattern' instead of just
 // 'GeneralPattern' to keep Windows PGO builds from confusing the
 // GeneralPattern class in gfxContext.cpp with this one.
-
 class CanvasGeneralPattern
 {
 public:
@ -1276,6 +1300,8 @@ bool CanvasRenderingContext2D::SwitchRenderingMode(RenderingMode aRenderingMode)

  RefPtr<SourceSurface> snapshot;
  Matrix transform;
+  RefPtr<PersistentBufferProvider> oldBufferProvider = mBufferProvider;
+  AutoReturnSnapshot autoReturn(nullptr);

  if (mTarget) {
    snapshot = mTarget->Snapshot();
@ -1285,14 +1311,16 @@ bool CanvasRenderingContext2D::SwitchRenderingMode(RenderingMode aRenderingMode)
    // When mBufferProvider is true but we have no mTarget, our current state's
    // transform is always valid. See ReturnTarget().
    transform = CurrentState().transform;
-    snapshot = mBufferProvider->GetSnapshot();
+    snapshot = mBufferProvider->BorrowSnapshot();
+    autoReturn.mBufferProvider = mBufferProvider;
+    autoReturn.mSnapshot = &snapshot;
  }
  mTarget = nullptr;
  mBufferProvider = nullptr;
  mResetLayer = true;

  // Recreate target using the new rendering mode
-  RenderingMode attemptedMode = EnsureTarget(aRenderingMode);
+  RenderingMode attemptedMode = EnsureTarget(nullptr, aRenderingMode);
  if (!IsTargetValid())
    return false;

@ -1425,7 +1453,8 @@ CanvasRenderingContext2D::CheckSizeForSkiaGL(IntSize aSize) {
 }

 CanvasRenderingContext2D::RenderingMode
-CanvasRenderingContext2D::EnsureTarget(RenderingMode aRenderingMode)
+CanvasRenderingContext2D::EnsureTarget(const gfx::Rect* aCoveredRect,
+                                       RenderingMode aRenderingMode)
 {
  // This would make no sense, so make sure we don't get ourselves in a mess
  MOZ_ASSERT(mRenderingMode != RenderingMode::DefaultBackendMode);
@ -1437,8 +1466,21 @@ CanvasRenderingContext2D::EnsureTarget(RenderingMode aRenderingMode)
  }

  if (mBufferProvider && mode == mRenderingMode) {
-    mTarget = mBufferProvider->GetDT(IntRect(IntPoint(), IntSize(mWidth, mHeight)));
+    gfx::Rect rect(0, 0, mWidth, mHeight);
+    if (aCoveredRect && CurrentState().transform.TransformBounds(*aCoveredRect).Contains(rect)) {
+      mTarget = mBufferProvider->BorrowDrawTarget(IntRect());
+    } else {
+      mTarget = mBufferProvider->BorrowDrawTarget(IntRect(0, 0, mWidth, mHeight));
+    }
+
    if (mTarget) {
+      // Restore clip and transform.
+      mTarget->SetTransform(CurrentState().transform);
+      for (uint32_t i = 0; i < mStyleStack.Length(); i++) {
+        for (uint32_t c = 0; c < mStyleStack[i].clipsPushed.Length(); c++) {
+          mTarget->PushClip(mStyleStack[i].clipsPushed[c]);
+        }
+      }
      return mRenderingMode;
    } else {
      mBufferProvider = nullptr;
@ -1495,7 +1537,7 @@ CanvasRenderingContext2D::EnsureTarget(RenderingMode aRenderingMode)
    }

    if (mBufferProvider) {
-      mTarget = mBufferProvider->GetDT(IntRect(IntPoint(), IntSize(mWidth, mHeight)));
+      mTarget = mBufferProvider->BorrowDrawTarget(IntRect(IntPoint(), IntSize(mWidth, mHeight)));
    } else if (!mTarget) {
      mTarget = gfxPlatform::GetPlatform()->CreateOffscreenCanvasDrawTarget(size, format);
      mode = RenderingMode::SoftwareBackendMode;
@ -1623,7 +1665,12 @@ CanvasRenderingContext2D::ReturnTarget()
 {
  if (mTarget && mBufferProvider) {
    CurrentState().transform = mTarget->GetTransform();
-    mBufferProvider->ReturnAndUseDT(mTarget.forget());
+    for (uint32_t i = 0; i < mStyleStack.Length(); i++) {
+      for (uint32_t c = 0; c < mStyleStack[i].clipsPushed.Length(); c++) {
+        mTarget->PopClip();
+      }
+    }
+    mBufferProvider->ReturnDrawTarget(mTarget.forget());
  }
 }

@ -2598,9 +2645,11 @@ CanvasRenderingContext2D::ClearRect(double aX, double aY, double aW,
    return;
  }

-  EnsureTarget();
+  gfx::Rect clearRect(aX, aY, aW, aH);

-  mTarget->ClearRect(gfx::Rect(aX, aY, aW, aH));
+  EnsureTarget(&clearRect);
+
+  mTarget->ClearRect(clearRect);

  RedrawUser(gfxRect(aX, aY, aW, aH));
 }
@ -2661,18 +2710,22 @@ CanvasRenderingContext2D::FillRect(double aX, double aY, double aW,
    }
  }

-  gfx::Rect bounds;
+  CompositionOp op = UsedOperation();
+  bool discardContent = PatternIsOpaque(Style::FILL)
+    && (op == CompositionOp::OP_OVER || op == CompositionOp::OP_DEST_OUT);

-  EnsureTarget();
+  const gfx::Rect fillRect(aX, aY, aW, aH);
+  EnsureTarget(discardContent ? &fillRect : nullptr);
+
+  gfx::Rect bounds;
  if (NeedToCalculateBounds()) {
-    bounds = gfx::Rect(aX, aY, aW, aH);
-    bounds = mTarget->GetTransform().TransformBounds(bounds);
+    bounds = mTarget->GetTransform().TransformBounds(fillRect);
  }

  AdjustedTarget(this, bounds.IsEmpty() ? nullptr : &bounds)->
    FillRect(gfx::Rect(aX, aY, aW, aH),
             CanvasGeneralPattern().ForStyle(this, Style::FILL, mTarget),
-             DrawOptions(state.globalAlpha, UsedOperation()));
+             DrawOptions(state.globalAlpha, op));

  RedrawUser(gfxRect(aX, aY, aW, aH));
 }
@ -5646,7 +5699,14 @@ CanvasRenderingContext2D::GetBufferProvider(LayerManager* aManager)
    return nullptr;
  }

-  mBufferProvider = new PersistentBufferProviderBasic(mTarget);
+  if (aManager) {
+    mBufferProvider = aManager->CreatePersistentBufferProvider(gfx::IntSize(mWidth, mHeight),
+                                                               GetSurfaceFormat());
+  }
+
+  if (!mBufferProvider) {
+    mBufferProvider = new PersistentBufferProviderBasic(mTarget);
+  }

  return mBufferProvider;
 }
--- a/dom/canvas/CanvasRenderingContext2D.h
+++ b/dom/canvas/CanvasRenderingContext2D.h
@ -635,7 +635,8 @@ protected:
   *
   * Returns the actual rendering mode being used by the created target.
   */
-  RenderingMode EnsureTarget(RenderingMode aRenderMode = RenderingMode::DefaultBackendMode);
+  RenderingMode EnsureTarget(const gfx::Rect* aCoveredRect = nullptr,
+                             RenderingMode aRenderMode = RenderingMode::DefaultBackendMode);

  /**
   * Disposes an old target and prepares to lazily create a new target.
@ -661,6 +662,12 @@ protected:
    */
  mozilla::gfx::SurfaceFormat GetSurfaceFormat() const;

+  /**
+   * Returns true if we know for sure that the pattern for a given style is opaque.
+   * Usefull to know if we can discard the content below in certain situations.
+   */
+  bool PatternIsOpaque(Style aStyle) const;
+
  /**
   * Update CurrentState().filter with the filter description for
   * CurrentState().filterChain.
--- a/gfx/2d/Tools.h
+++ b/gfx/2d/Tools.h
@ -98,6 +98,22 @@ BytesPerPixel(SurfaceFormat aFormat)
  }
 }

+static inline bool
+IsOpaqueFormat(SurfaceFormat aFormat) {
+  switch (aFormat) {
+    case SurfaceFormat::B8G8R8X8:
+    case SurfaceFormat::R8G8B8X8:
+    case SurfaceFormat::X8R8G8B8:
+    case SurfaceFormat::YUV:
+    case SurfaceFormat::NV12:
+    case SurfaceFormat::YUV422:
+    case SurfaceFormat::R5G6B5_UINT16:
+      return true;
+    default:
+      return false;
+  }
+}
+
 template<typename T, int alignment = 16>
 struct AlignedArray
 {
--- a/gfx/layers/CopyableCanvasLayer.cpp
+++ b/gfx/layers/CopyableCanvasLayer.cpp
@ -85,10 +85,21 @@ CopyableCanvasLayer::IsDataValid(const Data& aData)
 void
 CopyableCanvasLayer::UpdateTarget(DrawTarget* aDestTarget)
 {
+  AutoReturnSnapshot autoReturn;
+
  if (mAsyncRenderer) {
    mSurface = mAsyncRenderer->GetSurface();
  } else if (!mGLFrontbuffer && mBufferProvider) {
-    mSurface = mBufferProvider->GetSnapshot();
+    mSurface = mBufferProvider->BorrowSnapshot();
+    if (aDestTarget) {
+      // If !aDestTarget we'll end up painting using mSurface later,
+      // so we can't return it to the provider (note that this will trigger a
+      // copy of the snapshot behind the scenes when the provider is unlocked).
+      autoReturn.mSnapshot = &mSurface;
+    }
+    // Either way we need to call ReturnSnapshot because ther may be an
+    // underlying TextureClient that has to be unlocked.
+    autoReturn.mBufferProvider = mBufferProvider;
  }

  if (!mGLContext && aDestTarget) {
@ -99,6 +110,7 @@ CopyableCanvasLayer::UpdateTarget(DrawTarget* aDestTarget)
                               IntPoint(0, 0));
      mSurface = nullptr;
    }
+
    return;
  }

--- a/gfx/layers/Layers.cpp
+++ b/gfx/layers/Layers.cpp
@ -177,17 +177,12 @@ LayerManager::CreatePersistentBufferProvider(const mozilla::gfx::IntSize &aSize,
                                             mozilla::gfx::SurfaceFormat aFormat)
 {
  RefPtr<PersistentBufferProviderBasic> bufferProvider =
-    new PersistentBufferProviderBasic(aSize, aFormat,
-                                      gfxPlatform::GetPlatform()->GetPreferredCanvasBackend());
+    PersistentBufferProviderBasic::Create(aSize, aFormat,
+      gfxPlatform::GetPlatform()->GetPreferredCanvasBackend());

-  if (!bufferProvider->IsValid()) {
-    bufferProvider =
-      new PersistentBufferProviderBasic(aSize, aFormat,
-                                        gfxPlatform::GetPlatform()->GetFallbackCanvasBackend());
-  }
-
-  if (!bufferProvider->IsValid()) {
-    return nullptr;
+  if (!bufferProvider) {
+    bufferProvider = PersistentBufferProviderBasic::Create(aSize, aFormat,
+      gfxPlatform::GetPlatform()->GetFallbackCanvasBackend());
  }

  return bufferProvider.forget();
--- a/gfx/layers/PersistentBufferProvider.cpp
+++ b/gfx/layers/PersistentBufferProvider.cpp
@ -16,10 +16,215 @@ using namespace gfx;

 namespace layers {

-PersistentBufferProviderBasic::PersistentBufferProviderBasic(gfx::IntSize aSize, gfx::SurfaceFormat aFormat,
-                                                             gfx::BackendType aBackend)
+PersistentBufferProviderBasic::PersistentBufferProviderBasic(DrawTarget* aDt)
+: mDrawTarget(aDt)
 {
-  mDrawTarget = gfxPlatform::GetPlatform()->CreateDrawTargetForBackend(aBackend, aSize, aFormat);
+  MOZ_COUNT_CTOR(PersistentBufferProviderBasic);
+}
+
+PersistentBufferProviderBasic::~PersistentBufferProviderBasic()
+{
+  MOZ_COUNT_DTOR(PersistentBufferProviderBasic);
+}
+
+already_AddRefed<gfx::DrawTarget>
+PersistentBufferProviderBasic::BorrowDrawTarget(const gfx::IntRect& aPersistedRect)
+{
+  MOZ_ASSERT(!mSnapshot);
+  RefPtr<gfx::DrawTarget> dt(mDrawTarget);
+  return dt.forget();
+}
+
+bool
+PersistentBufferProviderBasic::ReturnDrawTarget(already_AddRefed<gfx::DrawTarget> aDT)
+{
+  RefPtr<gfx::DrawTarget> dt(aDT);
+  MOZ_ASSERT(mDrawTarget == dt);
+  return true;
+}
+
+already_AddRefed<gfx::SourceSurface>
+PersistentBufferProviderBasic::BorrowSnapshot()
+{
+  mSnapshot = mDrawTarget->Snapshot();
+  RefPtr<SourceSurface> snapshot = mSnapshot;
+  return snapshot.forget();
+}
+
+void
+PersistentBufferProviderBasic::ReturnSnapshot(already_AddRefed<gfx::SourceSurface> aSnapshot)
+{
+  RefPtr<SourceSurface> snapshot = aSnapshot;
+  MOZ_ASSERT(!snapshot || snapshot == mSnapshot);
+  mSnapshot = nullptr;
+}
+
+//static
+already_AddRefed<PersistentBufferProviderBasic>
+PersistentBufferProviderBasic::Create(gfx::IntSize aSize, gfx::SurfaceFormat aFormat,
+                                      gfx::BackendType aBackend)
+{
+  RefPtr<DrawTarget> dt = gfxPlatform::GetPlatform()->CreateDrawTargetForBackend(aBackend, aSize, aFormat);
+
+  if (!dt) {
+    return nullptr;
+  }
+
+  RefPtr<PersistentBufferProviderBasic> provider =
+    new PersistentBufferProviderBasic(dt);
+
+  return provider.forget();
+}
+
+
+//static
+already_AddRefed<PersistentBufferProviderShared>
+PersistentBufferProviderShared::Create(gfx::IntSize aSize,
+                                       gfx::SurfaceFormat aFormat,
+                                       CompositableForwarder* aFwd)
+{
+  if (!aFwd || !aFwd->IPCOpen()) {
+    return nullptr;
+  }
+
+  RefPtr<TextureClient> texture = TextureClient::CreateForDrawing(
+    aFwd, aFormat, aSize,
+    BackendSelector::Canvas,
+    TextureFlags::IMMEDIATE_UPLOAD,
+    TextureAllocationFlags::ALLOC_DEFAULT
+  );
+
+  if (!texture) {
+    return nullptr;
+  }
+
+  RefPtr<PersistentBufferProviderShared> provider =
+    new PersistentBufferProviderShared(aSize, aFormat, aFwd, texture);
+  return provider.forget();
+}
+
+PersistentBufferProviderShared::PersistentBufferProviderShared(gfx::IntSize aSize,
+                                                               gfx::SurfaceFormat aFormat,
+                                                               CompositableForwarder* aFwd,
+                                                               RefPtr<TextureClient>& aTexture)
+
+: mSize(aSize)
+, mFormat(aFormat)
+, mFwd(aFwd)
+, mBack(aTexture.forget())
+{
+  MOZ_COUNT_CTOR(PersistentBufferProviderShared);
+}
+
+PersistentBufferProviderShared::~PersistentBufferProviderShared()
+{
+  MOZ_COUNT_DTOR(PersistentBufferProviderShared);
+
+  mDrawTarget = nullptr;
+  if (mBack && mBack->IsLocked()) {
+    mBack->Unlock();
+  }
+  if (mFront && mFront->IsLocked()) {
+    mFront->Unlock();
+  }
+}
+
+already_AddRefed<gfx::DrawTarget>
+PersistentBufferProviderShared::BorrowDrawTarget(const gfx::IntRect& aPersistedRect)
+{
+  if (!mFwd->IPCOpen()) {
+    return nullptr;
+  }
+
+  if (!mDrawTarget) {
+    if (!mBack) {
+      mBack = TextureClient::CreateForDrawing(
+        mFwd, mFormat, mSize,
+        BackendSelector::Canvas,
+        TextureFlags::IMMEDIATE_UPLOAD,
+        TextureAllocationFlags::ALLOC_DEFAULT
+      );
+    }
+
+    if (!mBack) {
+      return nullptr;
+    }
+
+    if (!mBack->Lock(OpenMode::OPEN_READ_WRITE)) {
+      return nullptr;
+    }
+    if (!aPersistedRect.IsEmpty() && mFront
+        && mFront->Lock(OpenMode::OPEN_READ)) {
+
+      DebugOnly<bool> success = mFront->CopyToTextureClient(mBack, &aPersistedRect, nullptr);
+      MOZ_ASSERT(success);
+
+      mFront->Unlock();
+    }
+
+    mDrawTarget = mBack->BorrowDrawTarget();
+    if (!mDrawTarget) {
+      return nullptr;
+    }
+  }
+
+  RefPtr<gfx::DrawTarget> dt(mDrawTarget);
+  return dt.forget();
+}
+
+bool
+PersistentBufferProviderShared::ReturnDrawTarget(already_AddRefed<gfx::DrawTarget> aDT)
+{
+  RefPtr<gfx::DrawTarget> dt(aDT);
+  MOZ_ASSERT(mDrawTarget == dt);
+
+  mDrawTarget = nullptr;
+  dt = nullptr;
+
+  mBack->Unlock();
+
+  mFront = mBack;
+  mBack = nullptr;
+
+  return true;
+}
+
+already_AddRefed<gfx::SourceSurface>
+PersistentBufferProviderShared::BorrowSnapshot()
+{
+  if (!mFront || mFront->IsLocked()) {
+    MOZ_ASSERT(false);
+    return nullptr;
+  }
+
+  if (!mFront->Lock(OpenMode::OPEN_READ)) {
+    return nullptr;
+  }
+
+  mDrawTarget = mFront->BorrowDrawTarget();
+
+  if (!mDrawTarget) {
+    mFront->Unlock();
+  }
+
+  mSnapshot = mDrawTarget->Snapshot();
+
+  RefPtr<SourceSurface> snapshot = mSnapshot;
+  return snapshot.forget();
+}
+
+void
+PersistentBufferProviderShared::ReturnSnapshot(already_AddRefed<gfx::SourceSurface> aSnapshot)
+{
+  RefPtr<SourceSurface> snapshot = aSnapshot;
+  MOZ_ASSERT(!snapshot || snapshot == mSnapshot);
+
+  mSnapshot = nullptr;
+  snapshot = nullptr;
+
+  mDrawTarget = nullptr;
+
+  mFront->Unlock();
 }

 } // namespace layers
--- a/gfx/layers/PersistentBufferProvider.h
+++ b/gfx/layers/PersistentBufferProvider.h
@ -13,6 +13,12 @@
 #include "mozilla/gfx/Types.h"

 namespace mozilla {
+
+namespace gfx {
+  class SourceSurface;
+  class DrawTarget;
+}
+
 namespace layers {

 class CopyableCanvasLayer;
@ -38,43 +44,112 @@ public:
   *
   * \param aPersistedRect This indicates the area of the DrawTarget that needs
   *                       to have remained the same since the call to
-   *                       ReturnAndUseDT.
+   *                       ReturnDrawTarget.
   */
-  virtual already_AddRefed<gfx::DrawTarget> GetDT(const gfx::IntRect& aPersistedRect) = 0;
+  virtual already_AddRefed<gfx::DrawTarget> BorrowDrawTarget(const gfx::IntRect& aPersistedRect) = 0;
+
  /**
   * Return a DrawTarget to the PersistentBufferProvider and indicate the
   * contents of this DrawTarget is to be considered current by the
   * BufferProvider. The caller should forget any references to the DrawTarget.
   */
-  virtual bool ReturnAndUseDT(already_AddRefed<gfx::DrawTarget> aDT) = 0;
+  virtual bool ReturnDrawTarget(already_AddRefed<gfx::DrawTarget> aDT) = 0;

-  virtual already_AddRefed<gfx::SourceSurface> GetSnapshot() = 0;
-protected:
+  virtual already_AddRefed<gfx::SourceSurface> BorrowSnapshot() = 0;
+
+  virtual void ReturnSnapshot(already_AddRefed<gfx::SourceSurface> aSnapshot) = 0;
+
+  virtual TextureClient* GetTextureClient() { return nullptr; }
 };

+
 class PersistentBufferProviderBasic : public PersistentBufferProvider
 {
 public:
-  MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(PersistentBufferProviderBasic)
+  MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(PersistentBufferProviderBasic, override)

-  PersistentBufferProviderBasic(gfx::IntSize aSize, gfx::SurfaceFormat aFormat,
-                                gfx::BackendType aBackend);
-  explicit PersistentBufferProviderBasic(gfx::DrawTarget* aTarget) : mDrawTarget(aTarget) {}
+  static already_AddRefed<PersistentBufferProviderBasic>
+  Create(gfx::IntSize aSize, gfx::SurfaceFormat aFormat, gfx::BackendType aBackend);
+
+  explicit PersistentBufferProviderBasic(gfx::DrawTarget* aTarget);
+
+  virtual LayersBackend GetType() override { return LayersBackend::LAYERS_BASIC; }
+
+  virtual already_AddRefed<gfx::DrawTarget> BorrowDrawTarget(const gfx::IntRect& aPersistedRect) override;
+
+  virtual bool ReturnDrawTarget(already_AddRefed<gfx::DrawTarget> aDT) override;
+
+  virtual already_AddRefed<gfx::SourceSurface> BorrowSnapshot() override;
+
+  virtual void ReturnSnapshot(already_AddRefed<gfx::SourceSurface> aSnapshot) override;

-  bool IsValid() { return !!mDrawTarget; }
-  virtual LayersBackend GetType() { return LayersBackend::LAYERS_BASIC; }
-  already_AddRefed<gfx::DrawTarget> GetDT(const gfx::IntRect& aPersistedRect) {
-    RefPtr<gfx::DrawTarget> dt(mDrawTarget);
-    return dt.forget();
-  }
-  bool ReturnAndUseDT(already_AddRefed<gfx::DrawTarget> aDT) {
-    RefPtr<gfx::DrawTarget> dt(aDT);
-    MOZ_ASSERT(mDrawTarget == dt);
-    return true;
-  }
-  virtual already_AddRefed<gfx::SourceSurface> GetSnapshot() { return mDrawTarget->Snapshot(); }
 private:
+  ~PersistentBufferProviderBasic();
+
  RefPtr<gfx::DrawTarget> mDrawTarget;
+  RefPtr<gfx::SourceSurface> mSnapshot;
+};
+
+
+/**
+ * Provides access to a buffer which can be sent to the compositor without
+ * requiring a copy.
+ */
+class PersistentBufferProviderShared : public PersistentBufferProvider
+{
+public:
+  MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(PersistentBufferProviderShared, override)
+
+  static already_AddRefed<PersistentBufferProviderShared>
+  Create(gfx::IntSize aSize, gfx::SurfaceFormat aFormat,
+         CompositableForwarder* aFwd);
+
+  virtual LayersBackend GetType() override { return LayersBackend::LAYERS_CLIENT; }
+
+  virtual already_AddRefed<gfx::DrawTarget> BorrowDrawTarget(const gfx::IntRect& aPersistedRect) override;
+
+  virtual bool ReturnDrawTarget(already_AddRefed<gfx::DrawTarget> aDT) override;
+
+  virtual already_AddRefed<gfx::SourceSurface> BorrowSnapshot() override;
+
+  virtual void ReturnSnapshot(already_AddRefed<gfx::SourceSurface> aSnapshot) override;
+
+  TextureClient* GetTextureClient() override {
+    return mFront;
+  }
+
+protected:
+  PersistentBufferProviderShared(gfx::IntSize aSize, gfx::SurfaceFormat aFormat,
+                                 CompositableForwarder* aFwd,
+                                 RefPtr<TextureClient>& aTexture);
+
+  ~PersistentBufferProviderShared();
+
+  gfx::IntSize mSize;
+  gfx::SurfaceFormat mFormat;
+  RefPtr<CompositableForwarder> mFwd;
+  RefPtr<TextureClient> mFront;
+  RefPtr<TextureClient> mBack;
+  RefPtr<gfx::DrawTarget> mDrawTarget;
+  RefPtr<gfx::SourceSurface > mSnapshot;
+};
+
+struct AutoReturnSnapshot
+{
+  PersistentBufferProvider* mBufferProvider;
+  RefPtr<gfx::SourceSurface>* mSnapshot;
+
+  explicit AutoReturnSnapshot(PersistentBufferProvider* aProvider = nullptr)
+  : mBufferProvider(aProvider)
+  , mSnapshot(nullptr)
+  {}
+
+  ~AutoReturnSnapshot()
+  {
+    if (mBufferProvider) {
+      mBufferProvider->ReturnSnapshot(mSnapshot ? mSnapshot->forget() : nullptr);
+    }
+  }
 };

 } // namespace layers
--- a/gfx/layers/client/CanvasClient.cpp
+++ b/gfx/layers/client/CanvasClient.cpp
@ -66,6 +66,30 @@ CanvasClientBridge::UpdateAsync(AsyncCanvasRenderer* aRenderer)
  mAsyncID = asyncID;
 }

+void
+CanvasClient2D::UpdateFromTexture(TextureClient* aTexture)
+{
+  MOZ_ASSERT(aTexture);
+
+  if (!aTexture->IsSharedWithCompositor()) {
+    if (!AddTextureClient(aTexture)) {
+      return;
+    }
+  }
+
+  mBackBuffer = aTexture;
+
+  AutoTArray<CompositableForwarder::TimedTextureClient,1> textures;
+  CompositableForwarder::TimedTextureClient* t = textures.AppendElement();
+  t->mTextureClient = mBackBuffer;
+  t->mPictureRect = nsIntRect(nsIntPoint(0, 0), aTexture->GetSize());
+  t->mFrameID = mFrameID;
+  t->mInputFrameID = VRManagerChild::Get()->GetInputFrameID();
+
+  GetForwarder()->UseTextures(this, textures);
+  aTexture->SyncWithObject(GetForwarder()->GetSyncObject());
+}
+
 void
 CanvasClient2D::Update(gfx::IntSize aSize, ClientCanvasLayer* aLayer)
 {
--- a/gfx/layers/client/CanvasClient.h
+++ b/gfx/layers/client/CanvasClient.h
@ -13,6 +13,7 @@
 #include "mozilla/layers/CompositorTypes.h"  // for TextureInfo, etc
 #include "mozilla/layers/LayersSurfaces.h"  // for SurfaceDescriptor
 #include "mozilla/layers/TextureClient.h"  // for TextureClient, etc
+#include "mozilla/layers/PersistentBufferProvider.h"

 // Fix X11 header brain damage that conflicts with MaybeOneOf::None
 #undef None
@ -76,6 +77,8 @@ public:

  virtual void UpdateAsync(AsyncCanvasRenderer* aRenderer) {}

+  virtual void UpdateFromTexture(TextureClient* aTexture) {}
+
  virtual void Updated() { }

 protected:
@ -104,6 +107,8 @@ public:

  virtual void Update(gfx::IntSize aSize, ClientCanvasLayer* aLayer) override;

+  virtual void UpdateFromTexture(TextureClient* aBuffer) override;
+
  virtual bool AddTextureClient(TextureClient* aTexture) override
  {
    MOZ_ASSERT((mTextureFlags & aTexture->GetFlags()) == mTextureFlags);
--- a/gfx/layers/client/ClientCanvasLayer.cpp
+++ b/gfx/layers/client/ClientCanvasLayer.cpp
@ -130,7 +130,11 @@ ClientCanvasLayer::RenderLayer()
  Painted();

  FirePreTransactionCallback();
-  mCanvasClient->Update(gfx::IntSize(mBounds.width, mBounds.height), this);
+  if (mBufferProvider && mBufferProvider->GetTextureClient()) {
+    mCanvasClient->UpdateFromTexture(mBufferProvider->GetTextureClient());
+  } else {
+    mCanvasClient->Update(gfx::IntSize(mBounds.width, mBounds.height), this);
+  }

  FireDidTransactionCallback();

--- a/gfx/layers/client/ClientLayerManager.cpp
+++ b/gfx/layers/client/ClientLayerManager.cpp
@ -848,6 +848,15 @@ ClientLayerManager::DependsOnStaleDevice() const
  return gfxPlatform::GetPlatform()->GetDeviceCounter() != mDeviceCounter;
 }

+
+already_AddRefed<PersistentBufferProvider>
+ClientLayerManager::CreatePersistentBufferProvider(const gfx::IntSize& aSize,
+                                                   gfx::SurfaceFormat aFormat)
+{
+  return PersistentBufferProviderShared::Create(aSize, aFormat, AsShadowForwarder());
+}
+
+
 ClientLayer::~ClientLayer()
 {
  if (HasShadow()) {
--- a/gfx/layers/client/ClientLayerManager.h
+++ b/gfx/layers/client/ClientLayerManager.h
@ -246,6 +246,9 @@ public:
  void AddDidCompositeObserver(DidCompositeObserver* aObserver);
  void RemoveDidCompositeObserver(DidCompositeObserver* aObserver);

+  virtual already_AddRefed<PersistentBufferProvider>
+  CreatePersistentBufferProvider(const gfx::IntSize& aSize, gfx::SurfaceFormat aFormat) override;
+
 protected:
  enum TransactionPhase {
    PHASE_NONE, PHASE_CONSTRUCTION, PHASE_DRAWING, PHASE_FORWARD