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..a89f54e9448f347e30a81159cbac480998fa3ff3 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_numFramesSinceLastRenderingModeSwitch(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_numFramesSinceLastRenderingModeSwitch++;
+    if (m_context->is2d() && buffer()->isAccelerated()
+        && m_numFramesSinceLastRenderingModeSwitch >= ExpensiveCanvasHeuristicParameters::MinFramesBeforeSwitch) {
+        if (RuntimeEnabledFeatures::enableCanvas2dDynamicRenderingModeEnabled()) {
+            if (!m_context->isAccelerationOptimalForCanvasContent()) {
+                Platform::current()->currentThread()->getWebTaskRunner()->postTask(

[Justin Novosad, 2016/07/14 18:07:10]

Add a comment to explain why the switch is asynchronous (can't switch during
paint invalidation step)

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

Done.

+                    BLINK_FROM_HERE, WTF::bind(&disableAccelerationWrapper, m_imageBuffer->m_weakPtrFactory.createWeakPtr()));

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

Out of curiosity, would it be possible to use a lambda here?
disableAccelerationWrapper() seems simple enough that it would be nice to put
its contents inline.

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

Done.

+                m_numFramesSinceLastRenderingModeSwitch = 0;
+            }
+        }
+    }
 }
 
 void HTMLCanvasElement::didDisableAcceleration()