Paint local background colors onto foreground layer.

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMappingTest.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/layout/compositing/CompositedLayerMapping.h"
 
 #include "core/frame/FrameView.h"
 #include "core/layout/LayoutBoxModelObject.h"
 #include "core/layout/LayoutTestHelper.h"
 #include "core/layout/api/LayoutViewItem.h"
@@ skipping 27 matching lines @@
     bool interestRectChangedEnoughToRepaint(const IntRect& previousInterestRect, const IntRect& newInterestRect, const IntSize& layerSize)
     {
         return CompositedLayerMapping::interestRectChangedEnoughToRepaint(previousInterestRect, newInterestRect, layerSize);
     }
 
     IntRect previousInterestRect(const GraphicsLayer* graphicsLayer)
     {
         return graphicsLayer->m_previousInterestRect;
     }
 
+    bool shouldPaintBackgroundOntoScrollingContentsLayer(const char* elementId)
+    {
+        CompositedLayerMapping* mapping = toLayoutBlock(getLayoutObjectByElementId(elementId))->layer()->compositedLayerMapping();
+        return mapping->shouldPaintBackgroundOntoScrollingContentsLayer();
+    }
+
 private:
     void SetUp() override
     {
         RenderingTest::SetUp();
         enableCompositing();
     }
 
     void TearDown() override
     {
         RenderingTest::TearDown();
@@ skipping 561 matching lines @@
     Element* negativeCompositedChild = document().getElementById("negative-composited-child");
     negativeCompositedChild->parentNode()->removeChild(negativeCompositedChild);
     document().view()->updateAllLifecyclePhases();
 
     mapping = toLayoutBlock(getLayoutObjectByElementId("container"))->layer()->compositedLayerMapping();
     ASSERT_TRUE(mapping->scrollingContentsLayer());
     EXPECT_EQ(static_cast<GraphicsLayerPaintingPhase>(GraphicsLayerPaintOverflowContents | GraphicsLayerPaintCompositedScroll | GraphicsLayerPaintForeground), mapping->scrollingContentsLayer()->paintingPhase());
     EXPECT_FALSE(mapping->foregroundLayer());
 }
 
+TEST_F(CompositedLayerMappingTest, ShouldPaintBackgroundOntoScrollingContentsLayer)
+{
+    document().frame()->settings()->setPreferCompositingToLCDTextEnabled(true);
+    setBodyInnerHTML(
+        "<style>.scroller { overflow: scroll; will-change: transform; width: 300px; height: 300px;} .spacer { height: 1000px; }</style>"
+        "<div id='scroller1' class='scroller' style='background: white local;'>"
+        "    <div id='negative-composited-child' style='background-color: red; width: 1px; height: 1px; position: absolute; backface-visibility: hidden; z-index: -1'></div>"
+        "    <div class='spacer'></div>"
+        "</div>"
+        "<div id='scroller2' class='scroller' style='background: white content-box; padding: 10px;'>"
+        "    <div class='spacer'></div>"
+        "</div>"
+        "<div id='scroller3' class='scroller' style='background: white local content-box; padding: 10px;'>"
+        "    <div class='spacer'></div>"
+        "</div>"
+        );
+
+    // First scroller cannot paint background into scrolling contents layer because it has a negative z-index child.
+    EXPECT_FALSE(shouldPaintBackgroundOntoScrollingContentsLayer("scroller1"));
+
+    // Second scroller cannot paint background into scrolling contents layer because it has a content-box clip without local attachment.
+    EXPECT_FALSE(shouldPaintBackgroundOntoScrollingContentsLayer("scroller2"));
+
+    // Third scroller can paint background into scrolling contents layer.
+    EXPECT_TRUE(shouldPaintBackgroundOntoScrollingContentsLayer("scroller3"));
+}
+
 } // namespace blink