Removing canvas rendering mode switching feature

third_party/WebKit/Source/platform/graphics/CanvasHeuristicParameters.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 CanvasHeuristicParameters_h
+#define CanvasHeuristicParameters_h
+
+namespace blink {
+
+namespace CanvasHeuristicParameters {
+
+enum {
+  // Layer promotion heuristic parameters
+  //======================================
+
+  // FIXME (crbug.com/463239):
+  // The Layer promotion heuristics should go away after slimming paint
+  // is completely phased in and display list canvases are modified to
+  // use a lightweight layering primitive instead of the
+  // SkCanvas::saveLayer.
+
+  // Heuristic: Canvases that are overdrawn beyond this factor in a
+  // single frame are promoted to a direct composited layer so that
+  // their contents not be re-rasterized by the compositor when the
+  // containing layer is the object of a paint invalidation.
+  kExpensiveOverdrawThreshold = 3,
+
+  kExpensivePathPointCount = 50,
+
+  kSVGImageSourcesAreExpensive = 1,
+
+  kConcavePathsAreExpensive = 1,
+
+  kComplexClipsAreExpensive = 1,
+
+  kBlurredShadowsAreExpensive = 1,
+
+  // Heuristic: When drawing a source image that has more pixels than
+  // the destination canvas by the following factor or more, the draw
+  // is considered expensive.
+  kExpensiveImageSizeRatio = 4,
+
+  // Display list fallback heuristic parameters
+  //============================================
+
+  // Frames ending with more than this number of levels remaining
+  // on the state stack at the end of a frame are too expensive to
+  // remain in display list mode. This criterion is motivated by an
+  // O(N) cost in carying over state from one frame to the next when
+  // in display list mode. The value of this parameter should be high
+  // enough to almost never kick in other than for cases with unmatched
+  // save()/restore() calls are low enough to kick in before state
+  // management becomes measurably expensive.
+  kExpensiveRecordingStackDepth = 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.
+  kPreferDisplayListOverGpuSizeThreshold = 8096 * 4096,
+
+  // Disable Acceleration heuristic parameters
+  //===========================================
+
+  // 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.
+  kDrawImageTextureUploadSoftSizeLimit = 4096 * 4096,
+  kDrawImageTextureUploadSoftSizeLimitScaleThreshold = 4,
+  kDrawImageTextureUploadHardSizeLimit = 8192 * 8192,
+
+  // GPU readback prevention heuristics
+  //====================================
+
+  kGPUReadbackForcesNoAcceleration = 1,
+
+  // When gpu readback is successively invoked in following number of frames,
+  // we disable gpu acceleration to avoid the high cost of gpu readback.
+  kGPUReadbackMinSuccessiveFrames = 3,
+
+  // 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.
+  kDisableAccelerationToAvoidReadbacks = 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.
+  kEnableAccelerationToAvoidReadbacks = 1,
+
+};  // enum
+
+}  // namespace CanvasHeuristicParameters
+
+}  // namespace blink
+
+#endif