Merge r185152 - Subpixel rendering: Composited layer with subpixel ga…

…p does not get painted properly when its position changes. https://bugs.webkit.org/show_bug.cgi?id=145587 Reviewed by Simon Fraser. The composited layer always snaps to an enclosing device pixel (floors) while the renderer rounds. At certain positions (for example 0.5px on a 1x display), a gap is formed between the layer(0px) and its renderer(1px). In such cases, when the the renderer moves to a position (1.1px) where the gap is closed, we need to issue repaint on the layer in order to get the renderering right. Source/WebCore: Test: compositing/child-layer-with-subpixel-gap-needs-repaint-when-parent-moves.html * rendering/RenderLayerBacking.cpp: (WebCore::RenderLayerBacking::updateAfterLayout): (WebCore::devicePixelFractionGapFromRendererChanged): (WebCore::RenderLayerBacking::updateGeometry): * rendering/RenderLayerBacking.h: LayoutTests: * compositing/child-layer-with-subpixel-gap-needs-repaint-when-parent-moves-expected.html: Added. * compositing/child-layer-with-subpixel-gap-needs-repaint-when-parent-moves.html: Added.
WebKit · Jul 6, 2015 · cbe91c9 · cbe91c9
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diff --git a/LayoutTests/ChangeLog b/LayoutTests/ChangeLog
@@ -1,3 +1,18 @@
+2015-06-03  Zalan Bujtas  <zalan@apple.com>
+
+        Subpixel rendering: Composited layer with subpixel gap does not get painted properly when its position changes.
+        https://bugs.webkit.org/show_bug.cgi?id=145587
+
+        Reviewed by Simon Fraser.
+
+        The composited layer always snaps to an enclosing device pixel (floors) while the renderer rounds.
+        At certain positions (for example 0.5px on a 1x display), a gap is formed between the layer(0px) and its renderer(1px).
+        In such cases, when the the renderer moves to a position (1.1px) where the gap is closed, we need to issue repaint on the layer
+        in order to get the renderering right.
+
+        * compositing/child-layer-with-subpixel-gap-needs-repaint-when-parent-moves-expected.html: Added.
+        * compositing/child-layer-with-subpixel-gap-needs-repaint-when-parent-moves.html: Added.
+
 2015-05-30  Zalan Bujtas  <zalan@apple.com>
 
         REGRESSION (179771): zooming on facebook images covers image

diff --git a/...s/compositing/child-layer-with-subpixel-gap-needs-repaint-when-parent-moves-expected.html b/...s/compositing/child-layer-with-subpixel-gap-needs-repaint-when-parent-moves-expected.html
@@ -0,0 +1,28 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title>This tests that we repaint child layer if the subpixel gap changes between layers when parent layer moves.</title>
+<style>
+    .outer {
+        position: relative;
+        left: 0.7px;
+        height: 200px;
+        width: 200px;
+        background-color: rgba(0, 0, 255, 1);
+    }
+
+    .container-background {
+        position: relative;
+        transform: translateZ(0);
+        height: 100px;
+        width: 100px;
+        background-color: green;
+    }
+
+</style>
+<body>
+<div id=container class=outer>foo
+  <div class=container-background>bar
+  </div>
+</div>
+</body>
diff --git a/LayoutTests/compositing/child-layer-with-subpixel-gap-needs-repaint-when-parent-moves.html b/LayoutTests/compositing/child-layer-with-subpixel-gap-needs-repaint-when-parent-moves.html
@@ -0,0 +1,41 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title>This tests that we repaint child layer if the subpixel gap changes between layers when parent layer moves.</title>
+<style>
+    .outer {
+        position: relative;
+        left: 0.3px;
+        height: 200px;
+        width: 200px;
+        background-color: rgba(0, 0, 255, 1);
+    }
+
+    .container-background {
+        position: relative;
+        transform: translateZ(0);
+        height: 100px;
+        width: 100px;
+        background-color: green;
+    }
+
+</style>
+<script>
+    if (window.testRunner)
+        testRunner.waitUntilDone();
+
+    function runTest() {
+    	setTimeout(function () {
+    	    document.getElementById("container").style.left = "0.7px";
+            if (window.testRunner)
+                testRunner.notifyDone();
+        }, 0);
+    }
+    window.addEventListener('load', runTest, false);
+</script>
+<body>
+<div id=container class=outer>foo
+  <div class=container-background>bar
+  </div>
+</div>
+</body>
diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
@@ -1,3 +1,23 @@
+2015-06-03  Zalan Bujtas  <zalan@apple.com>
+
+        Subpixel rendering: Composited layer with subpixel gap does not get painted properly when its position changes.
+        https://bugs.webkit.org/show_bug.cgi?id=145587
+
+        Reviewed by Simon Fraser.
+
+        The composited layer always snaps to an enclosing device pixel (floors) while the renderer rounds.
+        At certain positions (for example 0.5px on a 1x display), a gap is formed between the layer(0px) and its renderer(1px).
+        In such cases, when the the renderer moves to a position (1.1px) where the gap is closed, we need to issue repaint on the layer
+        in order to get the renderering right.
+
+        Test: compositing/child-layer-with-subpixel-gap-needs-repaint-when-parent-moves.html
+
+        * rendering/RenderLayerBacking.cpp:
+        (WebCore::RenderLayerBacking::updateAfterLayout):
+        (WebCore::devicePixelFractionGapFromRendererChanged):
+        (WebCore::RenderLayerBacking::updateGeometry):
+        * rendering/RenderLayerBacking.h:
+
 2015-05-30  Zalan Bujtas  <zalan@apple.com>
 
         REGRESSION (179771): zooming on facebook images covers image

diff --git a/Source/WebCore/rendering/RenderLayerBacking.cpp b/Source/WebCore/rendering/RenderLayerBacking.cpp
@@ -517,7 +517,7 @@ void RenderLayerBacking::updateAfterLayout(UpdateAfterLayoutFlags flags)
         }
     }
 
-    if (flags & NeedsFullRepaint && !paintsIntoWindow() && !paintsIntoCompositedAncestor())
+    if (flags & NeedsFullRepaint && canIssueSetNeedsDisplay())
         setContentsNeedDisplay();
 }
 
@@ -636,6 +636,13 @@ static LayoutRect clipBox(RenderBox& renderer)
     return result;
 }
 
+static bool devicePixelFractionGapFromRendererChanged(const LayoutSize& previousDevicePixelFractionFromRenderer, const LayoutSize& currentDevicePixelFractionFromRenderer, float deviceScaleFactor)
+{
+    FloatSize previous = snapSizeToDevicePixel(previousDevicePixelFractionFromRenderer, LayoutPoint(), deviceScaleFactor);
+    FloatSize current = snapSizeToDevicePixel(currentDevicePixelFractionFromRenderer, LayoutPoint(), deviceScaleFactor);
+    return previous != current;
+}
+
 static FloatSize pixelFractionForLayerPainting(const LayoutPoint& point, float pixelSnappingFactor)
 {
     LayoutUnit x = point.x();
@@ -730,6 +737,7 @@ void RenderLayerBacking::updateGeometry()
     FloatSize devicePixelOffsetFromRenderer;
     LayoutSize devicePixelFractionFromRenderer;
     calculateDevicePixelOffsetFromRenderer(rendererOffsetFromGraphicsLayer, devicePixelOffsetFromRenderer, devicePixelFractionFromRenderer, deviceScaleFactor);
+    LayoutSize oldDevicePixelFractionFromRenderer = m_devicePixelFractionFromRenderer;
     m_devicePixelFractionFromRenderer = LayoutSize(-devicePixelFractionFromRenderer.width(), -devicePixelFractionFromRenderer.height());
 
     adjustAncestorCompositingBoundsForFlowThread(ancestorCompositingBounds, compAncestor);
@@ -984,6 +992,9 @@ void RenderLayerBacking::updateGeometry()
 
     updateAfterWidgetResize();
 
+    if (devicePixelFractionGapFromRendererChanged(oldDevicePixelFractionFromRenderer, m_devicePixelFractionFromRenderer, deviceScaleFactor) && canIssueSetNeedsDisplay())
+        setContentsNeedDisplay();
+
     compositor().updateScrollCoordinatedStatus(m_owningLayer);
 }
 

diff --git a/Source/WebCore/rendering/RenderLayerBacking.h b/Source/WebCore/rendering/RenderLayerBacking.h
@@ -331,6 +331,8 @@ class RenderLayerBacking final : public GraphicsLayerClient {
     static CSSPropertyID graphicsLayerToCSSProperty(AnimatedPropertyID);
     static AnimatedPropertyID cssToGraphicsLayerProperty(CSSPropertyID);
 
+    bool canIssueSetNeedsDisplay() const { return !paintsIntoWindow() && !paintsIntoCompositedAncestor(); }
+
     RenderLayer& m_owningLayer;
 
     std::unique_ptr<GraphicsLayer> m_ancestorClippingLayer; // Only used if we are clipped by an ancestor which is not a stacking context.