Improving canvas 2D performance by switching graphics rendering pipeline.

third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
index 4dede47795e53ea3150db3e8b3eb3fb629914f17..7fce4434ac99a816724c31199d24812288e9fb70 100644
--- a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
@@ -147,6 +147,7 @@ inline HTMLCanvasElement::HTMLCanvasElement(Document& document)
     , m_originClean(true)
     , m_didFailToCreateImageBuffer(false)
     , m_imageBufferIsClear(false)
+    , m_numFramesSincePipelineSwitch(0)
 {
     CanvasMetrics::countCanvasContextUsage(CanvasMetrics::CanvasCreated);
 }
@@ -292,6 +293,13 @@ void HTMLCanvasElement::didDraw(const FloatRect& rect)
         buffer()->didDraw(rect);
 }
 
+static void disableAccelerationWrapper(WeakPtr<ImageBuffer> buffer)
+{
+    if (buffer) {
+        buffer->disableAcceleration();
+    }
+}
+
 void HTMLCanvasElement::didFinalizeFrame()
 {
     notifyListenersCanvasChanged();
@@ -315,6 +323,18 @@ void HTMLCanvasElement::didFinalizeFrame()
         ro->invalidatePaintRectangle(mappedDirtyRect);
     }
     m_dirtyRect = FloatRect();
+
+    m_numFramesSincePipelineSwitch++;
+    if (m_context->is2d() && buffer()->isAccelerated() && m_numFramesSincePipelineSwitch >= 3) {

[Justin Novosad, 2016/07/12 19:31:23]

This hard coded 3 should go into a named constant in
ExpensiveCanvasHeuristicParameters

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

Done.

+        if (RuntimeEnabledFeatures::enableCanvas2dDynamicPipelineModeEnabled()) {
+            if (!m_context->shouldAccelerate()) {
+                Platform::current()->currentThread()->getWebTaskRunner()->postTask(
+                    BLINK_FROM_HERE, WTF::bind(&disableAccelerationWrapper,
+                    m_imageBuffer->m_weakPtrFactory.createWeakPtr()));
+                m_numFramesSincePipelineSwitch = 0;
+            }
+        }
+    }
 }
 
 void HTMLCanvasElement::didDisableAcceleration()