Backed out changeset 0c763c30594d (bug 1409871)

gfx/layers/client/ContentClient.cpp

@@ -636,11 +636,6 @@ ContentClientDoubleBuffered::FinalizeFrame(const nsIntRegion& aRegionToDraw)
     return;
   }
 
-  if (!EnsureBuffer() ||
-      (HaveBufferOnWhite() && !EnsureBufferOnWhite())) {
-    return;
-  }
-
   // We need to ensure that we lock these two buffers in the same
   // order as the compositor to prevent deadlocks.
   TextureClientAutoLock frontLock(mFrontClient, OpenMode::OPEN_READ_ONLY);
@@ -686,5 +681,47 @@ ContentClientDoubleBuffered::EnsureBackBufferIfFrontBuffer()
   }
 }
 
+void
+ContentClientDoubleBuffered::UpdateDestinationFrom(const RotatedBuffer& aSource,
+                                                   const nsIntRegion& aUpdateRegion)
+{
+  DrawIterator iter;
+  while (DrawTarget* destDT =
+    BorrowDrawTargetForQuadrantUpdate(aUpdateRegion.GetBounds(), BUFFER_BLACK, &iter)) {
+    bool isClippingCheap = IsClippingCheap(destDT, iter.mDrawRegion);
+    if (isClippingCheap) {
+      gfxUtils::ClipToRegion(destDT, iter.mDrawRegion);
+    }
+
+    aSource.DrawBufferWithRotation(destDT, BUFFER_BLACK, 1.0, CompositionOp::OP_SOURCE);
+    if (isClippingCheap) {
+      destDT->PopClip();
+    }
+    // Flush the destination before the sources become inaccessible (Unlock).
+    destDT->Flush();
+    ReturnDrawTargetToBuffer(destDT);
+  }
+
+  if (aSource.HaveBufferOnWhite()) {
+    MOZ_ASSERT(HaveBufferOnWhite());
+    DrawIterator whiteIter;
+    while (DrawTarget* destDT =
+      BorrowDrawTargetForQuadrantUpdate(aUpdateRegion.GetBounds(), BUFFER_WHITE, &whiteIter)) {
+      bool isClippingCheap = IsClippingCheap(destDT, whiteIter.mDrawRegion);
+      if (isClippingCheap) {
+        gfxUtils::ClipToRegion(destDT, whiteIter.mDrawRegion);
+      }
+
+      aSource.DrawBufferWithRotation(destDT, BUFFER_WHITE, 1.0, CompositionOp::OP_SOURCE);
+      if (isClippingCheap) {
+        destDT->PopClip();
+      }
+      // Flush the destination before the sources become inaccessible (Unlock).
+      destDT->Flush();
+      ReturnDrawTargetToBuffer(destDT);
+    }
+  }
+}
+
 } // namespace layers
 } // namespace mozilla