Cancel GPU acceleration for 2D canvas when drawing very large images

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 49 matching lines @@
     // 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,
 
     // Disable Acceleration heuristic parameters
     //===========================================
 
     GetImageDataForcesNoAcceleration = 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,
+
 }; // 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 59 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