Improving canvas 2D performance by switching graphics rendering pipeline.

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 51 matching lines @@
     // failure of subsequent allocations required for double buffering.
     PreferDisplayListOverGpuSizeThreshold = 4096 * 4096,
 
     // Disable Acceleration heuristic parameters
     //===========================================
 
     GetImageDataForcesNoAcceleration = 1,
 
 }; // enum
 
+
+// Constants and Coefficients for 2D Canvas Dynamic Rendering Mode
+// ===============================================================
+
+// Approximate relative costs of different types of operations for the
+// accelerated rendering pipeline and the recording rendering pipeline.
+// These costs were estimated experimentally based on the performance
+// of each pipeline in the animometer benchmark. Multiple factors influence
+// the true cost of each type of operation, including:
+// - The hardware configuration
+// - Version of the project
+// - Additional details about the operation:
+//   - Subtype of operation (png vs svg image, arc vs line...)
+//   - Scale
+//   - Associated effects (patterns, gradients...)
+
+const double AcceleratedDrawPathApproximateCost     = 0.004;

[Stephen White, 2016/07/14 18:53:05]

Could you put the methodology you used to create the constants into a doc, so
that we can re-run them as the rendering algorithms change? In particular, I
plan to change the path rendering algorithm which should should bump a lot of
these numbers.

[sebastienlc, 2016/07/14 22:26:53]

Done.

+const double AcceleratedGetImageDataApproximateCost = 0.1;
+const double AcceleratedDrawImageApproximateCost    = 0.002;
+
+const double RecordingDrawPathApproximateCost       = 0.0014;

[Stephen White, 2016/07/14 18:53:05]

Bikeshedding on names a bit: I'm not sure I like the nomenclature of
"Accelerated" vs "Recording". Isn't this really accelerated vs non-accelerated,
it's just that the latter uses the display list path, which is (currently) not
accelerated?

And what about the devices on which the recording path *is* accelerated? (I
thought this was the case on Android, but I could be wrong.) Should we use
different constants there?

[sebastienlc, 2016/07/14 22:26:53]

Done.

+const double RecordingGetImageDataApproximateCost   = 0.001;

[Stephen White, 2016/07/14 18:53:04]

I'm a little confused about GetImageData in "Recording" mode. My understand was
that this isn't possible (since we'd need to hand pixels back from the
compositor thread to the main thread), and we drop to non-display-list mode
already (prior to your change). Justin, could you clarify? Are we really ending
up in software-renderered, display-list mode here on a GetImageData? If not,
this "Recording" name is probably wrong.

Maybe we should just add a comment here to explain that this "Recording" mode
may not actually be recording.

[sebastienlc, 2016/07/14 22:26:53]

Done.

+const double RecordingDrawImageApproximateCost      = 0.004;
+
+// Coefficient used in the isAccelerationOptimalForCanvasContent
+// heuristic to create a bias in the output.
+// If set to a value greater than 1, it creates a bias towards suggesting acceleration.
+// If set to a value smaller than 1, it creates a bias towards not suggesting acceleration
+// For example, if its value is 1.5, then disabling gpu acceleration will only be suggested if
+// recordingCost * 1.5 < acceleratedCost.
+const double AcceleratedHeuristicBias = 1.5;
+
+// Minimum number of frames that need to be rendered
+// 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