Bug 599359, part 2: When we allocate a new front/back buffer pair, pre-fill the new front buffer with what we painted into the back buffer to stabilize the first Swap(). r=vlad a=blocking-fennec

gfx/layers/basic/BasicLayers.cpp

@@ -1432,6 +1432,10 @@ private:
   // copy of the descriptor here so that we can call
   // DestroySharedSurface() on the descriptor.
   SurfaceDescriptor mBackBuffer;
+  // When we allocate a new front buffer, we keep a temporary record
+  // of it until reach PaintBuffer().  Then we pre-fill back->front
+  // and destroy our record.
+  SurfaceDescriptor mNewFrontBuffer;
   nsIntSize mBufferSize;
 };
  
@@ -1449,8 +1453,39 @@ BasicShadowableThebesLayer::PaintBuffer(gfxContext* aContext,
     NS_ABORT_IF_FALSE(IsSurfaceDescriptorValid(mBackBuffer),
                       "should have a back buffer by now");
 
+    nsIntRegion updatedRegion = aRegionToDraw;
+    if (IsSurfaceDescriptorValid(mNewFrontBuffer)) {
+      // We just allocated a new buffer pair.  We want to "pre-fill"
+      // the new front buffer by copying to it what we just painted
+      // into the back buffer.  This starts off our Swap()s from a
+      // stable base: the first swap will return the same valid region
+      // as our new back buffer.  Thereafter, we only need to
+      // invalidate what was painted into the back buffer.
+      nsRefPtr<gfxASurface> frontBuffer =
+        BasicManager()->OpenDescriptor(mNewFrontBuffer);
+      nsRefPtr<gfxASurface> backBuffer =
+        BasicManager()->OpenDescriptor(mBackBuffer);
+
+      nsRefPtr<gfxContext> ctx = new gfxContext(frontBuffer);
+      ctx->SetOperator(gfxContext::OPERATOR_SOURCE);
+      ctx->DrawSurface(backBuffer, backBuffer->GetSize());
+
+      BasicManager()->CreatedThebesBuffer(BasicManager()->Hold(this),
+                                          mValidRegion,
+                                          mXResolution,
+                                          mYResolution,
+                                          mBuffer.BufferRect(),
+                                          mNewFrontBuffer);
+
+      // Clear temporary record of new front buffer
+      mNewFrontBuffer = SurfaceDescriptor();
+      // And pretend that we didn't update anything, in order to
+      // stabilize the first swap.
+      updatedRegion.SetEmpty();
+    }
+
     BasicManager()->PaintedThebesBuffer(BasicManager()->Hold(this),
-                                        aRegionToDraw,
+                                        updatedRegion,
                                         mBuffer.BufferRect(),
                                         mBuffer.BufferRotation(),
                                         mBackBuffer);
@@ -1471,19 +1506,15 @@ BasicShadowableThebesLayer::CreateBuffer(Buffer::ContentType aType,
     mBackBuffer = SurfaceDescriptor();
   }
 
-  SurfaceDescriptor tmpFront;
   // XXX error handling
+  NS_ABORT_IF_FALSE(!IsSurfaceDescriptorValid(mNewFrontBuffer),
+                    "Bad!  Did we create a buffer twice without painting?");
   if (!BasicManager()->AllocDoubleBuffer(gfxIntSize(aSize.width, aSize.height),
                                          aType,
-                                         &tmpFront,
+                                         &mNewFrontBuffer,
                                          &mBackBuffer))
     NS_RUNTIMEABORT("creating ThebesLayer 'back buffer' failed!");
   mBufferSize = aSize;
-
-  nsIntRect bufRect = mVisibleRegion.GetBounds();
-  BasicManager()->CreatedThebesBuffer(BasicManager()->Hold(this),
-                                      bufRect,
-                                      tmpFront);
   return BasicManager()->OpenDescriptor(mBackBuffer);
 }
 
@@ -1769,6 +1800,10 @@ public:
     MOZ_COUNT_DTOR(BasicShadowThebesLayer);
   }
 
+  virtual void SetFrontBuffer(const ThebesBuffer& aNewFront,
+                              const nsIntRegion& aValidRegion,
+                              float aXResolution, float aYResolution);
+
   virtual void SetValidRegion(const nsIntRegion& aRegion)
   {
     mOldValidRegion = mValidRegion;
@@ -1829,6 +1864,25 @@ private:
   float mOldYResolution;
 };
 
+void
+BasicShadowThebesLayer::SetFrontBuffer(const ThebesBuffer& aNewFront,
+                                       const nsIntRegion& aValidRegion,
+                                       float aXResolution, float aYResolution)
+{
+  mValidRegion = mOldValidRegion = aValidRegion;
+  mXResolution = mOldXResolution = aXResolution;
+  mYResolution = mOldYResolution = aYResolution;
+  nsRefPtr<gfxASurface> newFrontBuffer =
+    BasicManager()->OpenDescriptor(aNewFront.buffer());
+
+  nsRefPtr<gfxASurface> unused;
+  nsIntRect unusedRect;
+  nsIntPoint unusedRotation;
+  mFrontBuffer.Swap(newFrontBuffer, aNewFront.rect(), aNewFront.rotation(),
+                    getter_AddRefs(unused), &unusedRect, &unusedRotation);
+  mFrontBufferDescriptor = aNewFront.buffer();
+}
+
 void
 BasicShadowThebesLayer::Swap(const ThebesBuffer& aNewFront,
                              const nsIntRegion& aUpdatedRegion,

gfx/layers/ipc/PLayers.ipdl

@@ -82,10 +82,18 @@ union SurfaceDescriptor {
   SurfaceDescriptorX11;
 };
 
+struct ThebesBuffer {
+  SurfaceDescriptor buffer;
+  nsIntRect rect;
+  nsIntPoint rotation; 
+};
+
 struct OpCreateThebesBuffer {
   PLayer layer;
-  nsIntRect bufferRect;
-  SurfaceDescriptor initialFront;
+  ThebesBuffer initialFront;
+  nsIntRegion frontValidRegion;
+  float xResolution;
+  float yResolution;
 };
 struct OpDestroyThebesFrontBuffer { PLayer layer; };
 
@@ -152,11 +160,6 @@ struct OpRemoveChild  { PLayer container; PLayer childLayer; };
 
 
 // Paint (buffer update)
-struct ThebesBuffer {
-  SurfaceDescriptor buffer;
-  nsIntRect rect;
-  nsIntPoint rotation; 
-};
 struct OpPaintThebesBuffer {
   PLayer layer;
   ThebesBuffer newFrontBuffer;

gfx/layers/ipc/ShadowLayers.cpp

@@ -183,12 +183,19 @@ ShadowLayerForwarder::CreatedCanvasLayer(ShadowableLayer* aCanvas)
 
 void
 ShadowLayerForwarder::CreatedThebesBuffer(ShadowableLayer* aThebes,
-                                          nsIntRect aBufferRect,
+                                          const nsIntRegion& aFrontValidRegion,
+                                          float aXResolution,
+                                          float aYResolution,
+                                          const nsIntRect& aBufferRect,
                                           const SurfaceDescriptor& aTempFrontBuffer)
 {
   mTxn->AddEdit(OpCreateThebesBuffer(NULL, Shadow(aThebes),
-                                     aBufferRect,
-                                     aTempFrontBuffer));
+                                     ThebesBuffer(aTempFrontBuffer,
+                                                  aBufferRect,
+                                                  nsIntPoint(0, 0)),
+                                     aFrontValidRegion,
+                                     aXResolution,
+                                     aYResolution));
 }
 
 void

gfx/layers/ipc/ShadowLayers.h

@@ -143,13 +143,16 @@ public:
    *
    * It is expected that Created*Buffer() will be followed by a
    * Painted*Buffer() in the same transaction, so that
-   * |aInitialFrontBuffer| is never actually drawn to screen.
+   * |aInitialFrontBuffer| is never actually drawn to screen.  It is
+   * OK if it is drawn though.
    */
   /**
    * |aBufferRect| is the screen rect covered by |aInitialFrontBuffer|.
    */
   void CreatedThebesBuffer(ShadowableLayer* aThebes,
-                           nsIntRect aBufferRect,
+                           const nsIntRegion& aFrontValidRegion,
+                           float aXResolution, float aYResolution,
+                           const nsIntRect& aBufferRect,
                            const SurfaceDescriptor& aInitialFrontBuffer);
   /**
    * For the next two methods, |aSize| is the size of
@@ -394,6 +397,16 @@ public:
     mAllocator = aParent;
   }
 
+  /**
+   * CONSTRUCTION PHASE ONLY
+   *
+   * Override the front buffer and its valid region with the specified
+   * values.  This is called when a new buffer has been created.
+   */
+  virtual void SetFrontBuffer(const ThebesBuffer& aNewFront,
+                              const nsIntRegion& aValidRegion,
+                              float aXResolution, float aYResolution) = 0;
+
   virtual void InvalidateRegion(const nsIntRegion& aRegion)
   {
     NS_RUNTIMEABORT("ShadowThebesLayers can't fill invalidated regions");

gfx/layers/ipc/ShadowLayersParent.cpp

@@ -195,12 +195,8 @@ ShadowLayersParent::RecvUpdate(const nsTArray<Edit>& cset,
       ShadowThebesLayer* thebes = static_cast<ShadowThebesLayer*>(
         AsShadowLayer(otb)->AsLayer());
 
-      ThebesBuffer unusedBuffer;
-      nsIntRegion unusedRegion; float unusedXRes, unusedYRes;
-      thebes->Swap(
-        ThebesBuffer(otb.initialFront(), otb.bufferRect(), nsIntPoint(0, 0)),
-        unusedRegion,
-        &unusedBuffer, &unusedRegion, &unusedXRes, &unusedYRes);
+      thebes->SetFrontBuffer(otb.initialFront(), otb.frontValidRegion(),
+                             otb.xResolution(), otb.yResolution());
 
       break;
     }