Add an heuristic for promoting canvases to GPU acceleration

third_party/WebKit/Source/platform/graphics/ExpensiveCanvasHeuristicParameters.h

 // Copyright 2015 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 ExpensiveCanvasHeuristicParameters_h
 #define ExpensiveCanvasHeuristicParameters_h
 
 namespace blink {
 
 namespace ExpensiveCanvasHeuristicParameters {
@@ skipping 42 matching lines @@
   // management becomes measurably expensive.
   ExpensiveRecordingStackDepth = 50,
 
   // GPU vs. display list heuristic parameters
   //===========================================
 
   // Pixel count beyond which we should always prefer to use display
   // lists. Rationale: The allocation of large textures for canvas
   // tends to starve the compositor, and increase the probability of
   // failure of subsequent allocations required for double buffering.
-  PreferDisplayListOverGpuSizeThreshold = 4096 * 4096,
+  PreferDisplayListOverGpuSizeThreshold = 8096 * 4096,
 
   // Disable Acceleration heuristic parameters
   //===========================================
 
-  GetImageDataForcesNoAcceleration = 1,
-
-  // When a canvas is used as a source image, if its destination is
-  // non-accelerated and the source canvas is accelerated, a readback
-  // from the gpu is necessary. This option causes the source canvas to
-  // switch to non-accelerated when this situation is encountered to
-  // prevent future canvas-to-canvas draws from requiring a readback.
-  DisableAccelerationToAvoidReadbacks = 1,
-
   // When drawing very large images to canvases, there is a point where
   // GPU acceleration becomes inefficient due to texture upload overhead,
   // especially when the image is large enough that it is likely to
   // monopolize the texture cache, and when it is being downsized to the
   // point that few of the upload texels are actually sampled. When both
   // of these conditions are met, we disable acceleration.
   DrawImageTextureUploadSoftSizeLimit = 4096 * 4096,
   DrawImageTextureUploadSoftSizeLimitScaleThreshold = 4,
   DrawImageTextureUploadHardSizeLimit = 8192 * 8192,
 
+  // GPU readback prevention heuristics
+  //====================================
+
+  GetImageDataForcesNoAcceleration = 1,
+
+  // When a canvas is used as a source image, if its destination is
+  // non-accelerated and the source canvas is accelerated, a readback
+  // from the gpu is necessary. This option causes the source canvas to
+  // switch to non-accelerated when this situation is encountered to
+  // prevent future canvas-to-canvas draws from requiring a readback.
+  DisableAccelerationToAvoidReadbacks = 0,
+
+  // See description of DisableAccelerationToAvoidReadbacks. This is the
+  // opposite strategy : accelerate the destination canvas. If both
+  // EnableAccelerationToAvoidReadbacks and
+  // DisableAccelerationToAvoidReadbacks are specified, we try to enable
+  // acceleration on the destination first. If that does not succeed,
+  // we disable acceleration on the source canvas. Either way, future
+  // readbacks are prevented.
+  EnableAccelerationToAvoidReadbacks = 1,
+
 };  // enum
 
 // Constants and Coefficients for 2D Canvas Dynamic Rendering Mode Switching
 // =========================================================================
 
 // Approximate relative costs of different types of operations for the
 // accelerated rendering pipeline and the recording rendering pipeline.
 // These costs were estimated experimentally using the tools located in the
 // third_party/WebKit/Source/modules/canvas2d/performance_analysis directory.
 
@@ skipping 93 matching lines @@
 // before the rendering pipeline may be switched. Having this set
 // to more than 1 increases the sample size of usage data before a
 // decision is made, improving the accuracy of heuristics.
 const int MinFramesBeforeSwitch = 3;
 
 }  // namespace ExpensiveCanvasHeuristicParameters
 
 }  // namespace blink
 
 #endif