Reduce texture uploads during scrollbar invalidations.

cc/LayerTextureUpdater.h

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 
 #ifndef LayerTextureUpdater_h
 #define LayerTextureUpdater_h
 
 #if USE(ACCELERATED_COMPOSITING)
 
@@ skipping 42 matching lines @@
     virtual PassOwnPtr<Texture> createTexture(CCPrioritizedTextureManager*) = 0;
     // Returns the format of the texel uploaded by this interface.
     // This format should not be confused by texture internal format.
     // This format specifies the component order in the sampled texel.
     // If the format is TexelFormatBGRA, vec4.x is blue and vec4.z is red.
     virtual SampledTexelFormat sampledTexelFormat(GC3Denum textureFormat) = 0;
     // The |resultingOpaqueRect| gives back a region of the layer that was painted opaque. If the layer is marked opaque in the updater,
     // then this region should be ignored in preference for the entire layer's area.
     virtual void prepareToUpdate(const IntRect& contentRect, const IntSize& tileSize, float contentsWidthScale, float contentsHeightScale, IntRect& resultingOpaqueRect, CCRenderingStats&) { }
 
+    // Use after prepareToUpdate, allows checking if the texture contents will change, to avoid unecessary uploads.
+    virtual bool pixelsDidChange() const;

[jamesr, 2012/10/03 19:28:02]

this is unnecessary.  Keep the more specific type in ScrollbarLayerChromium

[enne (OOO), 2012/10/03 19:31:43]

Please don't do this.

updatePart is a non-virtual member function on ScrollbarLayerChromium.  There
are no derived classes from ScrollbarLayerChromium.  There's no impact other
than to ScrollbarLayerChromium to change the member variable types and the
updatePart signature to the derived updater type.  I think that's a lot cleaner
than exposing this to all updaters.

[wjmaclean, 2012/10/03 20:14:30]

Done.

NP, I just wasn't sure if you'd want me to change the member var type on SLC.

[wjmaclean, 2012/10/03 20:14:30]

Done.

+
     // Set true by the layer when it is known that the entire output is going to be opaque.
     virtual void setOpaque(bool) { }
 };
 
 } // namespace cc
 #endif // USE(ACCELERATED_COMPOSITING)
 #endif // LayerTextureUpdater_h