Simplify and speed up painting of clipping masks

third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp

 // 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.
 
 #include "core/paint/PaintLayerPainter.h"
 
 #include "core/frame/LocalFrame.h"
 #include "core/layout/LayoutView.h"
 #include "core/paint/ClipPathClipper.h"
 #include "core/paint/FilterPainter.h"
 #include "core/paint/LayerClipRecorder.h"
+#include "core/paint/LayoutObjectDrawingRecorder.h"
 #include "core/paint/ObjectPaintProperties.h"
 #include "core/paint/PaintInfo.h"
 #include "core/paint/PaintLayer.h"
 #include "core/paint/ScrollRecorder.h"
 #include "core/paint/ScrollableAreaPainter.h"
 #include "core/paint/Transform3DRecorder.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/geometry/FloatPoint3D.h"
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/graphics/paint/CompositingRecorder.h"
@@ skipping 872 matching lines @@
       default:
         clippingRule = LayerClipRecorder::IncludeSelfForBorderRadius;
         break;
     }
 
     clipRecorder.emplace(context, *m_paintLayer.layoutObject(), clipType,
                          clipRect, &paintingInfo, fragment.paginationOffset,
                          paintFlags, clippingRule);
   }
 
+  // If we are painting a mask for any reason and we have already processed the
+  // clips, there is no need to go through the remaining painting pipeline.
+  // We know that the mask just needs the area bounded by the clip rects to be
+  // filled with black.
+  if (clipRecorder && phase == PaintPhaseClippingMask) {
+    fillMaskingFragment(context, *clipRecorder);
+    return;
+  }
+
   LayoutRect newCullRect(clipRect.rect());
   Optional<ScrollRecorder> scrollRecorder;
   LayoutPoint paintOffset = -m_paintLayer.layoutBoxLocation();
   if (RuntimeEnabledFeatures::slimmingPaintV2Enabled()) {
     const auto* objectPaintProperties =
         m_paintLayer.layoutObject()->paintProperties();
     DCHECK(objectPaintProperties &&
            objectPaintProperties->localBorderBoxProperties());
     paintOffset +=
         toSize(objectPaintProperties->localBorderBoxProperties()->paintOffset);
@@ skipping 195 matching lines @@
     return;
 
   PaintLayerPaintingInfo paintingInfo(&m_paintLayer,
                                       LayoutRect(enclosingIntRect(damageRect)),
                                       paintFlags, LayoutSize());
   paintLayer(context, paintingInfo, PaintLayerPaintingOverlayScrollbars);
 
   m_paintLayer.setContainsDirtyOverlayScrollbars(false);
 }
 
+void PaintLayerPainter::fillMaskingFragment(
+    GraphicsContext& context,
+    const LayerClipRecorder& clipRecorder) {
+  DCHECK(m_paintLayer.compositingState() == PaintsIntoOwnBacking);
+  DCHECK(m_paintLayer.layoutObject()->isBox());
+
+  const LayoutBox* layoutBox = toLayoutBox(m_paintLayer.layoutObject());
+  if (LayoutObjectDrawingRecorder::useCachedDrawingIfPossible(
+          context, *layoutBox, PaintPhaseClippingMask))
+    return;
+
+  IntRect clipBoundingRect = clipRecorder.snappedClipRect();
+  for (auto& roundedRect : clipRecorder.roundedRects()) {
+    IntRect snappedRect = enclosingIntRect(roundedRect.rect());
+    clipBoundingRect.unite(snappedRect);
+  }
+  LayoutObjectDrawingRecorder drawingRecorder(
+      context, *layoutBox, PaintPhaseClippingMask, clipBoundingRect);
+  context.fillRect(clipBoundingRect, Color::black);
+}
+
 }  // namespace blink