Make 2D canvas disable gpu acceleration when getImageData is called

third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp

 /*
  * Copyright (C) 2012 Google 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
@@ skipping 444 matching lines @@
 {
     if (!m_surfaceCreationFailedAtLeastOnce) {
         // Only count the failure once per instance so that the histogram may
         // reflect the proportion of Canvas2DLayerBridge instances with surface
         // allocation failures.
         CanvasMetrics::countCanvasContextUsage(CanvasMetrics::GPUAccelerated2DCanvasSurfaceCreationFailed);
         m_surfaceCreationFailedAtLeastOnce = true;
     }
 }
 
+void Canvas2DLayerBridge::disableAcceleration()
+{
+    DCHECK(m_layer);
+    bool surfaceIsAccelerated;
+    RefPtr<SkSurface> newSurface = createSkSurface(nullptr, m_size, m_msaaSampleCount, m_opacityMode, &surfaceIsAccelerated);
+    if (newSurface) {
+        DCHECK(!surfaceIsAccelerated);
+        flushRecordingOnly();
+        SkPaint copyPaint;
+        copyPaint.setXfermodeMode(SkXfermode::kSrc_Mode);
+        m_surface->draw(newSurface->getCanvas(), 0, 0, &copyPaint); // GPU readback here
+        m_accelerationMode = DisableAcceleration; // Acceleration gets permanently disabled
+        GraphicsLayer::unregisterContentsLayer(m_layer->layer());
+        m_layer->clearTexture();
+        m_layer->layer()->removeFromParent();
+        m_layer.reset();
+        m_surface = newSurface;
+    }
+}

[xidachen, 2016/06/15 14:12:36]

By looking at the test results failure, it looks like we need some kind of
enableAcceleration() at some point to make the m_surface be a acclerated
SkSurface.

+
 SkSurface* Canvas2DLayerBridge::getOrCreateSurface(AccelerationHint hint)
 {
-    if (m_surface)
+    if (m_surface) {
+        if (hint == ForceNoAcceleration && m_layer)
+            disableAcceleration();
         return m_surface.get();
+    }
 
     if (m_layer && !isHibernating() && hint == PreferAcceleration) {
         return nullptr; // re-creation will happen through restore()
     }
 
     bool wantAcceleration = shouldAccelerate(hint);
-    bool surfaceIsAccelerated;
     if (CANVAS2D_BACKGROUND_RENDER_SWITCH_TO_CPU && isHidden() && wantAcceleration) {
         wantAcceleration = false;
         m_softwareRenderingWhileHidden = true;
     }
 
+    bool surfaceIsAccelerated;
     m_surface = createSkSurface(wantAcceleration ? m_contextProvider->grContext() : nullptr, m_size, m_msaaSampleCount, m_opacityMode, &surfaceIsAccelerated);
 
     if (!m_surface)
         reportSurfaceCreationFailure();
 
     if (m_surface && surfaceIsAccelerated && !m_layer) {
         m_layer = adoptPtr(Platform::current()->compositorSupport()->createExternalTextureLayer(this));
         m_layer->setOpaque(m_opacityMode == Opaque);
         m_layer->setBlendBackgroundColor(m_opacityMode != Opaque);
         GraphicsLayer::registerContentsLayer(m_layer->layer());
@@ skipping 503 matching lines @@
 #endif // USE_IOSURFACE_FOR_2D_CANVAS
 }
 
 void Canvas2DLayerBridge::Logger::reportHibernationEvent(HibernationEvent event)
 {
     DEFINE_STATIC_LOCAL(EnumerationHistogram, hibernationHistogram, ("Canvas.HibernationEvents", HibernationEventCount));
     hibernationHistogram.count(event);
 }
 
 } // namespace blink