Improved heuristic for disable acceleration.

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

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  * Copyright (C) 2012, 2013 Intel Corporation. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
@@ skipping 1052 matching lines @@
 unsigned CanvasRenderingContext2D::hitRegionsCount() const
 {
     if (m_hitRegionManager)
         return m_hitRegionManager->getHitRegionsCount();
 
     return 0;
 }
 
 bool CanvasRenderingContext2D::isAccelerationOptimalForCanvasContent() const
 {
-    // Simple heuristic to determine if the GPU accelerated pipeline should be
-    // used to maximize performance of 2D canvas based on past usage.
+    // Heuristic to determine if the GPU accelerated rendering pipeline is optimal
+    // for performance based on past usage. It has a bias towards suggesting that the
+    // accelerated pipeline is optimal.
 
-    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];
+    float acceleratedCost = estimateRenderingCost(ExpensiveCanvasHeuristicParameters::AcceleratedModeIndex);
 
-    double acceleratedCost =
-        numDrawPathCalls * ExpensiveCanvasHeuristicParameters::AcceleratedDrawPathApproximateCost +
-        m_usageCounters.numGetImageDataCalls * ExpensiveCanvasHeuristicParameters::AcceleratedGetImageDataApproximateCost+
-        m_usageCounters.numDrawCalls[DrawImage] * ExpensiveCanvasHeuristicParameters::AcceleratedDrawImageApproximateCost;
+    float recordingCost = estimateRenderingCost(ExpensiveCanvasHeuristicParameters::RecordingModeIndex);
 
-    double recordingCost =
-        numDrawPathCalls * ExpensiveCanvasHeuristicParameters::RecordingDrawPathApproximateCost +
-        m_usageCounters.numGetImageDataCalls * ExpensiveCanvasHeuristicParameters::UnacceleratedGetImageDataApproximateCost +
-        m_usageCounters.numDrawCalls[DrawImage] * ExpensiveCanvasHeuristicParameters::RecordingDrawImageApproximateCost;
+    float costDifference = acceleratedCost - recordingCost;
+    float percentCostReduction = costDifference / acceleratedCost * 100.0;
+    float costDifferencePerFrame = costDifference / m_usageCounters.numFramesSinceReset;
 
-    if (recordingCost * ExpensiveCanvasHeuristicParameters::AcceleratedHeuristicBias < acceleratedCost) {
+    if (percentCostReduction >= ExpensiveCanvasHeuristicParameters::MinPercentageImprovementToSuggestDisableAcceleration
+        && costDifferencePerFrame >= ExpensiveCanvasHeuristicParameters::MinCostPerFrameImprovementToSuggestDisableAcceleration) {
         return false;
     }
     return true;
 }
 
 void CanvasRenderingContext2D::resetUsageTracking()
 {
     UsageCounters newCounters;
     m_usageCounters = newCounters;
 }
 
 } // namespace blink