Improving canvas 2D performance by switching graphics rendering pipeline.

third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2D.cpp

Index: third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2D.cpp
diff --git a/third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2D.cpp b/third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2D.cpp
index a8f41ef5f440bb17342b0f8ca18bcd7ee3a13013..e027e2a0f0fd940c1b88d3be9f66796399d18b2f 100644
--- a/third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2D.cpp
+++ b/third_party/WebKit/Source/modules/canvas2d/CanvasRenderingContext2D.cpp
@@ -1068,4 +1068,38 @@ unsigned CanvasRenderingContext2D::hitRegionsCount() const
     return 0;
 }
 
+bool CanvasRenderingContext2D::shouldAccelerate() const
+{
+    // Simple heuristic to determine if the GPU accelerated pipeline should be
+    // used to maximize performance of 2D canvas based on past usage.
+    // The current implementation has a bias towards suggesting
+    // the use of the accelerated pipeline. The coefficients used
+    // to estimate the rendering cost of pipelines are approximate
+    // and were determined experimentally.
+
+    int numDrawPathCalls =
+        m_usageCounters.numDrawCalls[StrokePath] +
+        m_usageCounters.numDrawCalls[FillPath] +
+        m_usageCounters.numDrawCalls[FillText] +
+        m_usageCounters.numDrawCalls[StrokeText] +
+        m_usageCounters.numDrawCalls[FillRect] +
+        m_usageCounters.numDrawCalls[StrokeRect];
+
+    double acceleratedCost =
+        numDrawPathCalls * 0.004 +

[Justin Novosad, 2016/07/12 19:31:24]

These coefficients should all go in ExpensiveCAnvasHeuristicParameters, along
with comment that explaining how they were determined and any caveats.

[sebastienlc, 2016/07/13 19:51:02]

Done.

+        m_usageCounters.numGetImageDataCalls * 0.1 +
+        m_usageCounters.numDrawCalls[DrawImage] * 0.002;
+
+    double unacceleratedCost =
+        numDrawPathCalls * 0.0014 +
+        m_usageCounters.numGetImageDataCalls * 0.001 +
+        m_usageCounters.numDrawCalls[DrawImage] * 0.004;
+
+    double unacceleratedPenalty = 1.5; // greater than 1 to create a bias towards suggesting acceleration

[Justin Novosad, 2016/07/12 19:31:24]

This threshold should be in ExpensiveCanvasHeuristicParameters

[sebastienlc, 2016/07/13 19:51:02]

Done.

+    if (unacceleratedCost * unacceleratedPenalty < acceleratedCost) {
+        return false;
+    }
+    return true;
+}
+
 } // namespace blink