Subtree caching implementation in blink-core

Source/platform/graphics/paint/SubtreeRecorder.cpp

Index: Source/platform/graphics/paint/SubtreeRecorder.cpp
diff --git a/Source/platform/graphics/paint/SubtreeRecorder.cpp b/Source/platform/graphics/paint/SubtreeRecorder.cpp
index 5cc1e8caf64f7784318d66d3480247c9ab8fd53c..f8a3163ace99a9dcf2db5648ec221bc43d1991c4 100644
--- a/Source/platform/graphics/paint/SubtreeRecorder.cpp
+++ b/Source/platform/graphics/paint/SubtreeRecorder.cpp
@@ -13,46 +13,50 @@
 
 namespace blink {
 
+bool SubtreeRecorder::useCachedSubtreeIfPossible(GraphicsContext& context, const DisplayItemClientWrapper& client, int paintPhase)

[pdr., 2015/08/20 22:45:06]

int paintPhase -> PaintPhase phase, or maybe unsigned?

+{
+    // The conditions of returning false is not complete for a specific client.
+    // The client must check additional conditions before calling this function.
+
+    ASSERT(RuntimeEnabledFeatures::slimmingPaintV2Enabled());
+    ASSERT(context.displayItemList());
+
+    if (context.displayItemList()->displayItemConstructionIsDisabled() || RuntimeEnabledFeatures::slimmingPaintUnderInvalidationCheckingEnabled())
+        return false;
+
+    if (!context.displayItemList()->clientCacheIsValid(client.displayItemClient()))
+        return false;
+
+    // Append CachedSubtree display item only if we have cached the subtree.

[pdr., 2015/08/20 22:45:06]

WDYT about disabling the empty pair optimization for subtrees instead of doing
this extra check?

[Xianzhu, 2015/08/21 00:31:38]

That will generate empty subtrees for paint phases that produces nothing, e.g.
PaintPhaseOutline phase for a subtree containing no object having outline.
PaintPhaseSelection, PaintPhaseMask, etc. also have such problems.

+    // Otherwise it means that we generated an empty subtree previously
+    // (e.g in PaintPhaseOutline phase but there is no descendant has outline).
+    if (context.displayItemList()->subtreeCacheIsValid(client.displayItemClient(), DisplayItem::paintPhaseToBeginSubtreeType(paintPhase)))
+        context.displayItemList()->createAndAppend<CachedDisplayItem>(client, DisplayItem::paintPhaseToCachedSubtreeType(paintPhase));
+    return true;
+}
+
 SubtreeRecorder::SubtreeRecorder(GraphicsContext& context, const DisplayItemClientWrapper& client, int paintPhase)
     : m_displayItemList(context.displayItemList())
     , m_client(client)
     , m_paintPhase(paintPhase)
-    , m_canUseCache(false)
-#if ENABLE(ASSERT)
-    , m_checkedCanUseCache(false)
-#endif
 {
-    if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
-        return;
-
+    ASSERT(RuntimeEnabledFeatures::slimmingPaintV2Enabled());
     ASSERT(m_displayItemList);
 
-    // TODO(wangxianzhu): Implement subtree caching.
+    // Must check SubtreeRecorder::useCachedSubtreeIfPossible before creating the DrawingRecorder.
+    // ASSERT(!useCachedSubtreeIfPossible(context, client, paintPhase));
 
-    if (!m_canUseCache)
-        m_displayItemList->createAndAppend<BeginSubtreeDisplayItem>(m_client, DisplayItem::paintPhaseToBeginSubtreeType(paintPhase));
+    m_displayItemList->createAndAppend<BeginSubtreeDisplayItem>(client, DisplayItem::paintPhaseToBeginSubtreeType(paintPhase));
 }
 
 SubtreeRecorder::~SubtreeRecorder()
 {
-    if (!RuntimeEnabledFeatures::slimmingPaintV2Enabled())
-        return;
+    ASSERT(RuntimeEnabledFeatures::slimmingPaintV2Enabled());
 
-    ASSERT(m_checkedCanUseCache);
-    if (m_canUseCache)
-        m_displayItemList->createAndAppend<CachedDisplayItem>(m_client, DisplayItem::paintPhaseToCachedSubtreeType(m_paintPhase));
-    else if (m_displayItemList->lastDisplayItemIsNoopBegin())
+    if (m_displayItemList->lastDisplayItemIsNoopBegin())
         m_displayItemList->removeLastDisplayItem();
     else
         m_displayItemList->createAndAppend<EndSubtreeDisplayItem>(m_client, DisplayItem::paintPhaseToEndSubtreeType(m_paintPhase));
 }
 
-bool SubtreeRecorder::canUseCache() const
-{
-#if ENABLE(ASSERT)
-    m_checkedCanUseCache = true;
-#endif
-    return m_canUseCache;
-}
-
 } // namespace blink