Bug 893301. Fix alpha corruptions. r=nrc

gfx/layers/client/ContentClient.cpp

@@ -165,13 +165,13 @@ ContentClientRemoteBuffer::CreateAndAllocateTextureClient(RefPtr<TextureClient>&
     return false;
   }
 
-  if (!aClient->AsTextureClientDrawTarget()->AllocateForSurface(mSize)) {
+  if (!aClient->AsTextureClientDrawTarget()->AllocateForSurface(mSize, ALLOC_CLEAR_BUFFER)) {
     aClient = CreateTextureClientForDrawing(mSurfaceFormat,
                 mTextureInfo.mTextureFlags | TEXTURE_ALLOC_FALLBACK | aFlags);
     if (!aClient) {
       return false;
     }
-    if (!aClient->AsTextureClientDrawTarget()->AllocateForSurface(mSize)) {
+    if (!aClient->AsTextureClientDrawTarget()->AllocateForSurface(mSize, ALLOC_CLEAR_BUFFER)) {
       NS_WARNING("Could not allocate texture client");
       aClient = nullptr;
       return false;

gfx/layers/client/TextureClient.cpp

@@ -305,7 +305,7 @@ BufferTextureClient::GetAsSurface()
 }
 
 bool
-BufferTextureClient::AllocateForSurface(gfx::IntSize aSize)
+BufferTextureClient::AllocateForSurface(gfx::IntSize aSize, TextureAllocationFlags aFlags)
 {
   MOZ_ASSERT(IsValid());
   MOZ_ASSERT(mFormat != gfx::FORMAT_YUV, "This textureClient cannot use YCbCr data");
@@ -315,6 +315,11 @@ BufferTextureClient::AllocateForSurface(gfx::IntSize aSize)
   if (!Allocate(bufSize)) {
     return false;
   }
+
+  if (aFlags & ALLOC_CLEAR_BUFFER) {
+    memset(GetBuffer(), 0, bufSize);
+  }
+
   ImageDataSerializer serializer(GetBuffer());
   serializer.InitializeBufferInfo(aSize, mFormat);
   mSize = aSize;

gfx/layers/client/TextureClient.h

@@ -48,6 +48,11 @@ class Image;
  * using AsTextureCLientSurface(), etc.
  */
 
+enum TextureAllocationFlags {
+  ALLOC_DEFAULT = 0,
+  ALLOC_CLEAR_BUFFER = 1
+};
+
 /**
  * Interface for TextureClients that can be updated using a gfxASurface.
  */
@@ -56,7 +61,15 @@ class TextureClientSurface
 public:
   virtual bool UpdateSurface(gfxASurface* aSurface) = 0;
   virtual already_AddRefed<gfxASurface> GetAsSurface() = 0;
-  virtual bool AllocateForSurface(gfx::IntSize aSize) = 0;
+  /**
+   * Allocates for a given surface size, taking into account the pixel format
+   * which is part of the state of the TextureClient.
+   *
+   * Does not clear the surface by default, clearing the surface can be done
+   * by passing the CLEAR_BUFFER flag.
+   */
+  virtual bool AllocateForSurface(gfx::IntSize aSize,
+                                  TextureAllocationFlags flags = ALLOC_DEFAULT) = 0;
 };
 
 /**
@@ -67,7 +80,15 @@ class TextureClientDrawTarget
 public:
   virtual TemporaryRef<gfx::DrawTarget> GetAsDrawTarget() = 0;
   virtual gfx::SurfaceFormat GetFormat() const = 0;
-  virtual bool AllocateForSurface(gfx::IntSize aSize) = 0;
+  /**
+   * Allocates for a given surface size, taking into account the pixel format
+   * which is part of the state of the TextureClient.
+   *
+   * Does not clear the surface by default, clearing the surface can be done
+   * by passing the CLEAR_BUFFER flag.
+   */
+  virtual bool AllocateForSurface(gfx::IntSize aSize,
+                                  TextureAllocationFlags flags = ALLOC_DEFAULT) = 0;
 };
 
 /**
@@ -277,7 +298,8 @@ public:
 
   virtual already_AddRefed<gfxASurface> GetAsSurface() MOZ_OVERRIDE;
 
-  virtual bool AllocateForSurface(gfx::IntSize aSize) MOZ_OVERRIDE;
+  virtual bool AllocateForSurface(gfx::IntSize aSize,
+                                  TextureAllocationFlags flags = ALLOC_DEFAULT) MOZ_OVERRIDE;
 
   // TextureClientDrawTarget