Fix Compositing of Opaque Scrolling Layers and Add Tests

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

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableAreaTest.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableAreaTest.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableAreaTest.cpp
index f11b78585bf5bbf4aa33df3d6d844357746ec8e4..1a14130ba4d825265b4394adeb4779e0f8850cbe 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableAreaTest.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableAreaTest.cpp
@@ -4,25 +4,71 @@
 
 #include "core/paint/PaintLayerScrollableAreaTest.h"
 
+#include "platform/graphics/GraphicsLayer.h"
+
 namespace blink {
 
+TEST_F(PaintLayerScrollableAreaTest, 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>"
+        "<div id='scroller4' class='scroller' style='background: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUg), white local;'><div class='spacer'></div></div>"
+        "<div id='scroller5' class='scroller' style='background: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUg) local, white local;'><div class='spacer'></div></div>"
+        "<div id='scroller6' class='scroller' style='background: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUg) local, white padding-box; padding: 10px;'><div class='spacer'></div></div>"
+        "<div id='scroller7' class='scroller' style='background: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUg) local, white 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"));
+
+    // Fourth scroller cannot paint background into scrolling contents layer because the background image is not locally attached.
+    EXPECT_FALSE(shouldPaintBackgroundOntoScrollingContentsLayer("scroller4"));
+
+    // Fifth scroller can paint background into scrolling contents layer because both the image and color are locally attached.
+    EXPECT_TRUE(shouldPaintBackgroundOntoScrollingContentsLayer("scroller5"));
+
+    // Sixth scroller can paint background into scrolling contents layer because the image is locally attached and even though
+    // the color is not, it is filled to the padding box so it will be drawn the same as a locally attached background.
+    EXPECT_TRUE(shouldPaintBackgroundOntoScrollingContentsLayer("scroller6"));
+
+    // Seventh scroller cannot paint background into scrolling contents layer because the color is filled to the content
+    // box and we have padding so it is not equivalent to a locally attached background.
+    EXPECT_FALSE(shouldPaintBackgroundOntoScrollingContentsLayer("scroller7"));
+}
+
 TEST_F(PaintLayerScrollableAreaTest, OpaqueLayersPromoted)
 {
     RuntimeEnabledFeatures::setCompositeOpaqueScrollersEnabled(true);
 
     setBodyInnerHTML(
         "<style>"
-        "#scroller { overflow: scroll; height: 300px; width: 300px; background-color: rgb(0,128,0); }"
-        "#scrolled { height: 1000px; width: 250px; }"
+        "#scroller { overflow: scroll; height: 200px; width: 200px; background: white local content-box; border: 10px solid rgba(0, 255, 0, 0.5); }"
+        "#scrolled { height: 300px; }"
         "</style>"
         "<div id=\"scroller\"><div id=\"scrolled\"></div></div>");
     document().view()->updateAllLifecyclePhases();
 
-    ASSERT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
+    EXPECT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
     Element* scroller = document().getElementById("scroller");
     PaintLayer* paintLayer = toLayoutBoxModelObject(scroller->layoutObject())->layer();
     ASSERT_TRUE(paintLayer);
-    ASSERT_TRUE(paintLayer->needsCompositedScrolling());
+    EXPECT_TRUE(paintLayer->needsCompositedScrolling());
+    EXPECT_TRUE(paintLayer->graphicsLayerBacking());
+    ASSERT_TRUE(paintLayer->graphicsLayerBackingForScrolling());
+    EXPECT_TRUE(paintLayer->graphicsLayerBackingForScrolling()->contentsOpaque());
 }
 
 TEST_F(PaintLayerScrollableAreaTest, TransparentLayersNotPromoted)
@@ -31,17 +77,77 @@ TEST_F(PaintLayerScrollableAreaTest, TransparentLayersNotPromoted)
 
     setBodyInnerHTML(
         "<style>"
-        "#scroller { overflow: scroll; height: 300px; width: 300px; background-color: rgba(0,128,0,0.5); }"
-        "#scrolled { height: 1000px; width: 250px; }"
+        "#scroller { overflow: scroll; height: 200px; width: 200px; background: rgba(0, 255, 0, 0.5) local content-box; border: 10px solid rgba(0, 255, 0, 0.5); }"
+        "#scrolled { height: 300px; }"
         "</style>"
         "<div id=\"scroller\"><div id=\"scrolled\"></div></div>");
     document().view()->updateAllLifecyclePhases();
 
-    ASSERT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
+    EXPECT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
     Element* scroller = document().getElementById("scroller");
     PaintLayer* paintLayer = toLayoutBoxModelObject(scroller->layoutObject())->layer();
     ASSERT_TRUE(paintLayer);
-    ASSERT_TRUE(!paintLayer->needsCompositedScrolling());
+    EXPECT_FALSE(paintLayer->needsCompositedScrolling());
+    EXPECT_FALSE(paintLayer->graphicsLayerBacking());
+    EXPECT_FALSE(paintLayer->graphicsLayerBackingForScrolling());
 }
 
+TEST_F(PaintLayerScrollableAreaTest, OpaqueLayersDepromotedOnStyleChange)
+{
+    RuntimeEnabledFeatures::setCompositeOpaqueScrollersEnabled(true);
+
+    setBodyInnerHTML(
+        "<style>"
+        "#scroller { overflow: scroll; height: 200px; width: 200px; background: white local content-box; }"
+        "#scrolled { height: 300px; }"
+        "</style>"
+        "<div id=\"scroller\"><div id=\"scrolled\"></div></div>");
+    document().view()->updateAllLifecyclePhases();
+
+    EXPECT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
+    Element* scroller = document().getElementById("scroller");
+    PaintLayer* paintLayer = toLayoutBoxModelObject(scroller->layoutObject())->layer();
+    ASSERT_TRUE(paintLayer);
+    EXPECT_TRUE(paintLayer->needsCompositedScrolling());
+
+    // Change the background to transparent
+    scroller->setAttribute(HTMLNames::styleAttr, "background: rgba(255,255,255,0.5) local content-box;");
+    document().view()->updateAllLifecyclePhases();
+    paintLayer = toLayoutBoxModelObject(scroller->layoutObject())->layer();
+    ASSERT_TRUE(paintLayer);
+    EXPECT_FALSE(paintLayer->needsCompositedScrolling());
+    EXPECT_FALSE(paintLayer->graphicsLayerBacking());
+    EXPECT_FALSE(paintLayer->graphicsLayerBackingForScrolling());
+}
+
+TEST_F(PaintLayerScrollableAreaTest, OpaqueLayersPromotedOnStyleChange)
+{
+    RuntimeEnabledFeatures::setCompositeOpaqueScrollersEnabled(true);
+
+    setBodyInnerHTML(
+        "<style>"
+        "#scroller { overflow: scroll; height: 200px; width: 200px; background: rgba(255,255,255,0.5) local content-box; }"
+        "#scrolled { height: 300px; }"
+        "</style>"
+        "<div id=\"scroller\"><div id=\"scrolled\"></div></div>");
+    document().view()->updateAllLifecyclePhases();
+
+    EXPECT_TRUE(RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled());
+    Element* scroller = document().getElementById("scroller");
+    PaintLayer* paintLayer = toLayoutBoxModelObject(scroller->layoutObject())->layer();
+    ASSERT_TRUE(paintLayer);
+    EXPECT_FALSE(paintLayer->needsCompositedScrolling());
+
+    // Change the background to transparent
+    scroller->setAttribute(HTMLNames::styleAttr, "background: white local content-box;");
+    document().view()->updateAllLifecyclePhases();
+    paintLayer = toLayoutBoxModelObject(scroller->layoutObject())->layer();
+    ASSERT_TRUE(paintLayer);
+    EXPECT_TRUE(paintLayer->needsCompositedScrolling());
+    EXPECT_TRUE(paintLayer->graphicsLayerBacking());
+    ASSERT_TRUE(paintLayer->graphicsLayerBackingForScrolling());
+    EXPECT_TRUE(paintLayer->graphicsLayerBackingForScrolling()->contentsOpaque());
+}
+
+
 }