Bug 1006198 - Use 8byte aligned surface for CopyableCanvasLayer since that's the max WebGL supports for readback. r=nical

gfx/layers/CopyableCanvasLayer.cpp

@@ -17,6 +17,7 @@
 #include "gfxUtils.h"                   // for gfxUtils
 #include "gfx2DGlue.h"                  // for thebes --> moz2d transition
 #include "mozilla/gfx/BaseSize.h"       // for BaseSize
+#include "mozilla/gfx/Tools.h"
 #include "nsDebug.h"                    // for NS_ASSERTION, NS_WARNING, etc
 #include "nsISupportsImpl.h"            // for gfxContext::AddRef, etc
 #include "nsRect.h"                     // for nsIntRect
@@ -170,7 +171,9 @@ CopyableCanvasLayer::GetTempSurface(const IntSize& aSize,
       aSize != mCachedTempSurface->GetSize() ||
       aFormat != mCachedTempSurface->GetFormat())
   {
-    mCachedTempSurface = Factory::CreateDataSourceSurface(aSize, aFormat);
+    // Create a surface aligned to 8 bytes since that's the highest alignment WebGL can handle.
+    uint32_t stride = GetAlignedStride<8>(aSize.width * BytesPerPixel(aFormat));
+    mCachedTempSurface = Factory::CreateDataSourceSurfaceWithStride(aSize, aFormat, stride);
   }
 
   return mCachedTempSurface;