Promote opaque fixed position elements.

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 602 matching lines @@
 
     // Scroll 3000 pixels down to bring the scrollable area to somewhere in the middle.
     frameDocument.view()->setScrollPosition(DoublePoint(0.0, 3000.0), ProgrammaticScroll);
     document().view()->updateAllLifecyclePhases();
 
     ASSERT_TRUE(frameDocument.view()->layoutViewItem().hasLayer());
     // The width is 485 pixels due to the size of the scrollbar.
     EXPECT_RECT_EQ(IntRect(0, 0, 500, 7500), recomputeInterestRect(frameDocument.view()->layoutViewItem().enclosingLayer()->graphicsLayerBacking()));
 }
 
+TEST_F(CompositedLayerMappingTest, PromoteOpaqueFixedPosition)
+{
+    document().frame()->settings()->setPreferCompositingToLCDTextEnabled(false);
+    RuntimeEnabledFeatures::setCompositeOpaqueFixedPositionEnabled(true);

[chrishtr, 2016/09/29 17:25:25]

Restore these flags at the end of the test. I think there might be helper RAII
classes for this.

[flackr, 2016/09/29 18:01:28]

Done. I couldn't find any helper classes or existing use of helpers in other
tests, but let me know if you know of one.

+
+    setBodyInnerHTML(
+        "<div id='translucent' style='width: 20px; height: 20px; position: fixed; top: 100px; left: 100px;'></div>"
+        "<div id='opaque' style='width: 20px; height: 20px; position: fixed; top: 100px; left: 200px; background: white;'></div>"
+        "<div id='opaque-with-shadow' style='width: 20px; height: 20px; position: fixed; top: 100px; left: 300px; background: white; box-shadow: 10px 10px 5px #888888;'></div>"
+        "<div id='spacer' style='height: 2000px'></div>");
+
+    document().view()->updateAllLifecyclePhases();
+
+    // The translucent fixed box should not be promoted.
+    Element* element = document().getElementById("translucent");
+    PaintLayer* paintLayer = toLayoutBoxModelObject(element->layoutObject())->layer();
+    EXPECT_EQ(NotComposited, paintLayer->compositingState());
+
+    // The opaque fixed box should be promoted and be opaque so that text will be drawn
+    // with subpixel anti-aliasing.
+    element = document().getElementById("opaque");
+    paintLayer = toLayoutBoxModelObject(element->layoutObject())->layer();
+    EXPECT_EQ(PaintsIntoOwnBacking, paintLayer->compositingState());
+    EXPECT_TRUE(paintLayer->graphicsLayerBacking()->contentsOpaque());
+
+    // The opaque fixed box with shadow should not be promoted because the layer will
+    // include the shadow which is not opaque.
+    element = document().getElementById("opaque-with-shadow");
+    paintLayer = toLayoutBoxModelObject(element->layoutObject())->layer();
+    EXPECT_EQ(NotComposited, paintLayer->compositingState());
+}
+
+
 TEST_F(CompositedLayerMappingTest, ScrollingContentsAndForegroundLayerPaintingPhase)
 {
     document().frame()->settings()->setPreferCompositingToLCDTextEnabled(true);
     setBodyInnerHTML(
         "<div id='container' style='position: relative; z-index: 1; overflow: scroll; width: 300px; height: 300px'>"
         "    <div id='negative-composited-child' style='background-color: red; width: 1px; height: 1px; position: absolute; backface-visibility: hidden; z-index: -1'></div>"
         "    <div style='background-color: blue; width: 2000px; height: 2000px; position: relative; top: 10px'></div>"
         "</div>");
 
     CompositedLayerMapping* mapping = toLayoutBlock(getLayoutObjectByElementId("container"))->layer()->compositedLayerMapping();
@@ skipping 153 matching lines @@
         document().setRootScroller(nullptr, nonThrow);
         document().view()->updateAllLifecyclePhases();
         ASSERT_EQ(document().documentElement(), rootScrollerController.globalRootScroller());
 
         EXPECT_TRUE(mapping3->clippingLayer());
         EXPECT_TRUE(mapping3->clippingLayer()->platformLayer()->masksToBounds());
     }
 }
 
 } // namespace blink