Fold compositing display items into contained drawings if the drawing is a singleton.

third_party/WebKit/Source/platform/graphics/paint/CompositingRecorder.cpp

Index: third_party/WebKit/Source/platform/graphics/paint/CompositingRecorder.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/paint/CompositingRecorder.cpp b/third_party/WebKit/Source/platform/graphics/paint/CompositingRecorder.cpp
index 15fb79b3c8df7d58edebe9b394d98c8483bb7497..74db7214b11d60e66608042996b2e5326ee9cca0 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/CompositingRecorder.cpp
+++ b/third_party/WebKit/Source/platform/graphics/paint/CompositingRecorder.cpp
@@ -7,7 +7,9 @@
 #include "platform/graphics/GraphicsContext.h"
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/graphics/paint/CompositingDisplayItem.h"
+#include "platform/graphics/paint/DrawingRecorder.h"
 #include "platform/graphics/paint/PaintController.h"
+#include "platform/graphics/paint/SkPictureBuilder.h"
 
 namespace blink {
 
@@ -30,7 +32,40 @@ void CompositingRecorder::beginCompositing(GraphicsContext& graphicsContext, con
 
 void CompositingRecorder::endCompositing(GraphicsContext& graphicsContext, const DisplayItemClient& client)
 {
-    graphicsContext.getPaintController().endItem<EndCompositingDisplayItem>(client);
+    // If the end of the current display list is of the form [BeginCompositingDisplayItem] [DrawingDisplayItem],
+    // then fold the BeginCompositingDisplayItem into a new DrawingDisplayItem that replaces them both. This allows
+    // Skia to optimize for the case when the BeginCompositingDisplayItem represents a simple opacity/color that can be merged into
+    // the opacity/color of the drawing. See crbug.com/628831 for more details.
+    PaintController& paintController = graphicsContext.getPaintController();

[wkorman, 2016/07/26 18:41:08]

Need to turn off caching.

[chrishtr, 2016/07/26 18:49:45]

Done.

+    const DisplayItem* lastDisplayItem = paintController.lastDisplayItem(0);
+    const DisplayItem* secondToLastDisplayItem = paintController.lastDisplayItem(1);

[wkorman, 2016/07/26 18:41:08]

fun: opportunity to use 'penultimate' vs 'secondToLast', if you find such a word
entertaining

[chrishtr, 2016/07/26 18:49:45]

Acknowledged.

+    if (lastDisplayItem && secondToLastDisplayItem && lastDisplayItem->drawsContent() && secondToLastDisplayItem->isBeginCompositingDisplayItem()) {
+        FloatRect cullRect(((DrawingDisplayItem*)lastDisplayItem)->picture()->cullRect());
+        const DisplayItemClient& displayItemClient = lastDisplayItem->client();
+        DisplayItem::Type displayItemType = lastDisplayItem->getType();
+
+        // Re-record the last two DisplayItems into a new SkPicture.
+        SkPictureBuilder pictureBuilder(cullRect, nullptr, &graphicsContext);
+        {
+            DrawingRecorder newRecorder(pictureBuilder.context(), displayItemClient, displayItemType, cullRect);

[f(malita), 2016/07/26 19:03:15]

Why is this inner DrawingRecording needed?  Wouldn't pictureBuilder achieve the
same on its own?

[chrishtr, 2016/07/26 19:54:24]

SkPictureBuilder doesn't start a recording of a specific DrawingDisplayItem, it
instead sets up a nested DisplayItemList etc that can be drawn into. To draw
into a DisplayItemList you need a recorder.

+            DCHECK(!DrawingRecorder::useCachedDrawingIfPossible(pictureBuilder.context(), displayItemClient, displayItemType));
+
+            secondToLastDisplayItem->replay(pictureBuilder.context());
+            lastDisplayItem->replay(pictureBuilder.context());
+            EndCompositingDisplayItem(client).replay(pictureBuilder.context());
+        }
+
+        paintController.removeLastDisplayItem(); // Remove the DrawingDisplayItem.
+        paintController.removeLastDisplayItem(); // Remove the BeginCompositingDisplayItem.
+
+        {
+            // Replay the new SKPicture into a new DrawingDisplayItem in the original DisplayItemList.
+            DrawingRecorder newRecorder(graphicsContext, displayItemClient, displayItemType, cullRect);
+            pictureBuilder.endRecording()->playback(graphicsContext.canvas());
+        }
+    } else {
+        graphicsContext.getPaintController().endItem<EndCompositingDisplayItem>(client);
+    }
 }
 
 } // namespace blink