Calculate and track display item opaqueness

third_party/WebKit/Source/platform/graphics/paint/DrawingDisplayItem.h

Index: third_party/WebKit/Source/platform/graphics/paint/DrawingDisplayItem.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/DrawingDisplayItem.h b/third_party/WebKit/Source/platform/graphics/paint/DrawingDisplayItem.h
index a2a9c1ddf6e02a9fdafa50ac560e6c9b63f7c035..3af2a3d6b4567abc2be4a79f77e1e941bc9f9bfc 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/DrawingDisplayItem.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/DrawingDisplayItem.h
@@ -6,6 +6,7 @@
 #define DrawingDisplayItem_h
 
 #include "platform/PlatformExport.h"
+#include "platform/RuntimeEnabledFeatures.h"
 #include "platform/geometry/FloatPoint.h"
 #include "platform/graphics/paint/DisplayItem.h"
 #include "third_party/skia/include/core/SkPicture.h"
@@ -25,12 +26,14 @@ public:
     DrawingDisplayItem(const DisplayItemClient& client
         , Type type
         , PassRefPtr<const SkPicture> picture
+        , bool knownToBeOpaque = false
 #if ENABLE(ASSERT)
         , UnderInvalidationCheckingMode underInvalidationCheckingMode = CheckPicture
 #endif
         )
         : DisplayItem(client, type, sizeof(*this))
         , m_picture(picture && picture->approximateOpCount() ? picture : nullptr)
+        , m_knownToBeOpaque(knownToBeOpaque)
 #if ENABLE(ASSERT)
         , m_underInvalidationCheckingMode(underInvalidationCheckingMode)
 #endif
@@ -44,6 +47,8 @@ public:
 
     const SkPicture* picture() const { return m_picture.get(); }
 
+    bool knownToBeOpaque() const { ASSERT(RuntimeEnabledFeatures::slimmingPaintV2Enabled()); return m_knownToBeOpaque; }
+
 #if ENABLE(ASSERT)
     UnderInvalidationCheckingMode underInvalidationCheckingMode() const { return m_underInvalidationCheckingMode; }
     bool equals(const DisplayItem& other) const final;
@@ -56,6 +61,10 @@ private:
 
     RefPtr<const SkPicture> m_picture;
 
+    // True if there are no transparent areas. Only used for SlimmingPaintV2.

[pdr., 2016/01/27 05:07:46]

Jbroman, what do you think about this?

It's very gross but we have several free bits in DisplayItem and bloating
DrawingDisplayItem may hurt memory without spv2. Unless there's a better idea, I
think we should move it.

[jbroman, 2016/01/27 16:04:27]

Ugh, it probably costs us 4-8 bytes per due to pointer alignment, doesn't it?
You could quickly check to see how much memory in total that is in practice
(it's still not massive compared to the usual size of a DrawingDisplayItem +
associated SkPicture + SkRecord). I'm worried it may be premature optimization.

But if you'd really rather have DisplayItem::m_derivedClassDefinedBit1 or
something, we _could_.

+    // TODO(pdr): It's messy, but we may want to move this to DisplayItem which has free bits.
+    const bool m_knownToBeOpaque;
+
 #if ENABLE(ASSERT)
     UnderInvalidationCheckingMode m_underInvalidationCheckingMode;
 #endif