Implement a paint offset cache for slimming paint v2

Source/core/paint/LayoutObjectDrawingRecorder.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef LayoutObjectDrawingRecorder_h
 #define LayoutObjectDrawingRecorder_h
 
 #include "core/layout/LayoutObject.h"
 #include "core/paint/PaintPhase.h"
+#include "platform/geometry/LayoutPoint.h"
 #include "platform/geometry/LayoutRect.h"
 #include "platform/graphics/paint/DisplayItemCacheSkipper.h"
 #include "platform/graphics/paint/DrawingRecorder.h"
 #include "wtf/Allocator.h"
 #include "wtf/Optional.h"
 
 namespace blink {
 
 class GraphicsContext;
 
 // Convenience wrapper of DrawingRecorder for LayoutObject painters.
 class LayoutObjectDrawingRecorder final {
     ALLOW_ONLY_INLINE_ALLOCATION();
 public:
-    static bool useCachedDrawingIfPossible(GraphicsContext& context, const LayoutObject& layoutObject, DisplayItem::Type displayItemType)
+    static bool useCachedDrawingIfPossible(GraphicsContext& context, const LayoutObject& layoutObject, DisplayItem::Type displayItemType, const LayoutPoint& paintOffset)
     {
+        // TODO(pdr): The paint offset cache should be stored on LayoutObject but is temporarily on the DisplayItemList.
+        if (RuntimeEnabledFeatures::slimmingPaintV2Enabled() && !context.displayItemList()->paintOffsetIsUnchanged(layoutObject.displayItemClient(), paintOffset))
+            return false;
         if (layoutObject.fullPaintInvalidationReason() == PaintInvalidationDelayedFull)
             return false;
         return DrawingRecorder::useCachedDrawingIfPossible(context, layoutObject, displayItemType);
     }
 
-    static bool useCachedDrawingIfPossible(GraphicsContext& context, const LayoutObject& layoutObject, PaintPhase phase)
+    static bool useCachedDrawingIfPossible(GraphicsContext& context, const LayoutObject& layoutObject, PaintPhase phase, const LayoutPoint& paintOffset)
     {
-        return useCachedDrawingIfPossible(context, layoutObject, DisplayItem::paintPhaseToDrawingType(phase));
+        return useCachedDrawingIfPossible(context, layoutObject, DisplayItem::paintPhaseToDrawingType(phase), paintOffset);
     }
 
-    LayoutObjectDrawingRecorder(GraphicsContext& context, const LayoutObject& layoutObject, DisplayItem::Type displayItemType, const FloatRect& clip)
+    LayoutObjectDrawingRecorder(GraphicsContext& context, const LayoutObject& layoutObject, DisplayItem::Type displayItemType, const FloatRect& clip, const LayoutPoint& paintOffset)
     {
+        if (RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
+            // TODO(pdr): The paint offset cache should be stored on LayoutObject but is temporarily on the DisplayItemList.
+            if (!context.displayItemList()->paintOffsetIsUnchanged(layoutObject.displayItemClient(), paintOffset)) {
+                context.displayItemList()->recordPaintOffset(layoutObject.displayItemClient(), paintOffset);
+                context.displayItemList()->invalidatePaintOffset(layoutObject.displayItemClient());
+            } else {
+                ASSERT(!context.displayItemList()->paintOffsetWasInvalidated(layoutObject.displayItemClient()) || !context.displayItemList()->clientCacheIsValid(layoutObject.displayItemClient()));
+            }
+        }
+
         // We may paint a delayed-invalidation object before it's actually invalidated.
         if (layoutObject.fullPaintInvalidationReason() == PaintInvalidationDelayedFull)
             m_cacheSkipper.emplace(context);
         m_drawingRecorder.emplace(context, layoutObject, displayItemType, clip);
     }
-    LayoutObjectDrawingRecorder(GraphicsContext& context, const LayoutObject& layoutObject, DisplayItem::Type displayItemType, const LayoutRect& clip)
-        : LayoutObjectDrawingRecorder(context, layoutObject, displayItemType, FloatRect(clip)) { }
 
-    LayoutObjectDrawingRecorder(GraphicsContext& context, const LayoutObject& layoutObject, PaintPhase phase, const FloatRect& clip)
-        : LayoutObjectDrawingRecorder(context, layoutObject, DisplayItem::paintPhaseToDrawingType(phase), clip) { }
+    LayoutObjectDrawingRecorder(GraphicsContext& context, const LayoutObject& layoutObject, DisplayItem::Type displayItemType, const LayoutRect& clip, const LayoutPoint& paintOffset)
+        : LayoutObjectDrawingRecorder(context, layoutObject, displayItemType, FloatRect(clip), paintOffset) { }
 
-    LayoutObjectDrawingRecorder(GraphicsContext& context, const LayoutObject& layoutObject, PaintPhase phase, const LayoutRect& clip)
-        : LayoutObjectDrawingRecorder(context, layoutObject, DisplayItem::paintPhaseToDrawingType(phase), FloatRect(clip)) { }
+    LayoutObjectDrawingRecorder(GraphicsContext& context, const LayoutObject& layoutObject, PaintPhase phase, const FloatRect& clip, const LayoutPoint& paintOffset)
+        : LayoutObjectDrawingRecorder(context, layoutObject, DisplayItem::paintPhaseToDrawingType(phase), clip, paintOffset) { }
 
-    LayoutObjectDrawingRecorder(GraphicsContext& context, const LayoutObject& layoutObject, PaintPhase phase, const IntRect& clip)
-        : LayoutObjectDrawingRecorder(context, layoutObject, DisplayItem::paintPhaseToDrawingType(phase), FloatRect(clip)) { }
+    LayoutObjectDrawingRecorder(GraphicsContext& context, const LayoutObject& layoutObject, PaintPhase phase, const LayoutRect& clip, const LayoutPoint& paintOffset)
+        : LayoutObjectDrawingRecorder(context, layoutObject, DisplayItem::paintPhaseToDrawingType(phase), FloatRect(clip), paintOffset) { }
+
+    LayoutObjectDrawingRecorder(GraphicsContext& context, const LayoutObject& layoutObject, PaintPhase phase, const IntRect& clip, const LayoutPoint& paintOffset)
+        : LayoutObjectDrawingRecorder(context, layoutObject, DisplayItem::paintPhaseToDrawingType(phase), FloatRect(clip), paintOffset) { }
 
 #if ENABLE(ASSERT)
     void setUnderInvalidationCheckingMode(DrawingDisplayItem::UnderInvalidationCheckingMode mode) { m_drawingRecorder->setUnderInvalidationCheckingMode(mode); }
 #endif
 
 private:
     Optional<DisplayItemCacheSkipper> m_cacheSkipper;
     Optional<DrawingRecorder> m_drawingRecorder;
 };
 
 } // namespace blink
 
 #endif // LayoutObjectDrawingRecorder_h