Track scissored damage area for WebGL

Source/core/html/canvas/WebGLRenderingContextBase.cpp

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 784 matching lines @@
     if (m_framebufferBinding || isContextLost())
         return;
 
     drawingBuffer()->markContentsChanged();
 
     m_layerCleared = false;
     RenderBox* renderBox = canvas()->renderBox();
     if (renderBox && renderBox->hasAcceleratedCompositing()) {
         m_markedCanvasDirty = true;
         canvas()->clearCopiedImage();
-        renderBox->contentChanged(changeType);
+        IntRect rect = IntRect(IntPoint(0, 0), clampedCanvasSize());
+        if (!m_flippedScissorBox.isEmpty())
+            rect.intersect(m_flippedScissorBox);
+        renderBox->contentChanged(changeType, rect);
     } else {
         if (!m_markedCanvasDirty) {
             m_markedCanvasDirty = true;
             canvas()->didDraw(FloatRect(FloatPoint(0, 0), clampedCanvasSize()));
         }
     }
 }
 
 bool WebGLRenderingContextBase::clearIfComposited(GLbitfield mask)
 {
@@ skipping 2416 matching lines @@
         return;
     webContext()->sampleCoverage(value, invert);
 }
 
 void WebGLRenderingContextBase::scissor(GLint x, GLint y, GLsizei width, GLsizei height)
 {
     if (isContextLost())
         return;
     if (!validateSize("scissor", width, height))
         return;
+
+    m_flippedScissorBox = IntRect(x, canvas()->height() - height, width, height - y);
     webContext()->scissor(x, y, width, height);
 }
 
 void WebGLRenderingContextBase::shaderSource(WebGLShader* shader, const String& string)
 {
     if (isContextLost() || !validateWebGLObject("shaderSource", shader))
         return;
     String stringWithoutComments = StripComments(string).result();
     if (!validateString("shaderSource", stringWithoutComments))
         return;
@@ skipping 2619 matching lines @@
     return m_sharedWebGraphicsContext3D ? m_sharedWebGraphicsContext3D->drawingBuffer() : 0;
 }
 #else
 DrawingBuffer* WebGLRenderingContextBase::drawingBuffer() const
 {
     return m_drawingBuffer.get();
 }
 #endif
 
 } // namespace blink