Subpixel rendering: RenderLayer's clipping should snap to device pixe…

…l boundaries. https://bugs.webkit.org/show_bug.cgi?id=131466 Reviewed by Simon Fraser. Fractional pixel clipping can produce cruft on RenderLayers. Since RenderLayer sizing and painting are snapped, painting clip rect needs to be snapped the same way. Source/WebCore: Test: fast/clip/clip-when-rect-has-fractional-pixel-value.html * rendering/RenderLayer.cpp: (WebCore::RenderLayer::clipToRect): LayoutTests: * fast/clip/clip-when-rect-has-fractional-pixel-value-expected.html: Added. * fast/clip/clip-when-rect-has-fractional-pixel-value.html: Added. Canonical link: https://commits.webkit.org/149982@main git-svn-id: https://svn.webkit.org/repository/webkit/trunk@167562 268f45cc-cd09-0410-ab3c-d52691b4dbfc
WebKit · Apr 20, 2014 · d1ab07182011638c64a3b2458ec70250d368ab6f · d1ab071
1 parent bd46a9a
commit d1ab07182011638c64a3b2458ec70250d368ab6f
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diff --git a/LayoutTests/ChangeLog b/LayoutTests/ChangeLog
@@ -1,3 +1,16 @@
+2014-04-19  Zalan Bujtas  <zalan@apple.com>
+
+        Subpixel rendering: RenderLayer's clipping should snap to device pixel boundaries.
+        https://bugs.webkit.org/show_bug.cgi?id=131466
+
+        Reviewed by Simon Fraser.
+
+        Fractional pixel clipping can produce cruft on RenderLayers. Since RenderLayer
+        sizing and painting are snapped, painting clip rect needs to be snapped the same way.
+
+        * fast/clip/clip-when-rect-has-fractional-pixel-value-expected.html: Added.
+        * fast/clip/clip-when-rect-has-fractional-pixel-value.html: Added.
+
 2014-04-19  Chris Fleizach  <cfleizach@apple.com>
 
         AX: grid rows are not recognized do to lack of explicit role="row", role="gridcell"

diff --git a/LayoutTests/fast/clip/clip-when-rect-has-fractional-pixel-value-expected.html b/LayoutTests/fast/clip/clip-when-rect-has-fractional-pixel-value-expected.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title>This tests that clipping a block element does not leave cruft behind.</title>
+<style>
+  div {
+    position: absolute;
+    top: 0;
+    left: 0;
+    width: 100px;
+    height: 72px;
+    background-color: yellow;
+    -webkit-transform: translateZ(0);
+  }
+</style>
+</head>
+<body>
+  <div></div>
+</body>
diff --git a/LayoutTests/fast/clip/clip-when-rect-has-fractional-pixel-value.html b/LayoutTests/fast/clip/clip-when-rect-has-fractional-pixel-value.html
@@ -0,0 +1,21 @@
+<html>
+<head>
+<title>This tests that clipping a block element does not leave cruft behind.</title>
+<style>
+  div {
+    position: absolute;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    clip: rect(0, 100, 6.5em, 0);
+    font-size: 11px;
+    background-color: yellow;
+    -webkit-transform: translateZ(0);
+  }
+</style>
+</head>
+<body>
+  <div></div>
+</body>
+
diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
@@ -1,3 +1,18 @@
+2014-04-19  Zalan Bujtas  <zalan@apple.com>
+
+        Subpixel rendering: RenderLayer's clipping should snap to device pixel boundaries.
+        https://bugs.webkit.org/show_bug.cgi?id=131466
+
+        Reviewed by Simon Fraser.
+
+        Fractional pixel clipping can produce cruft on RenderLayers. Since RenderLayer
+        sizing and painting are snapped, painting clip rect needs to be snapped the same way.
+
+        Test: fast/clip/clip-when-rect-has-fractional-pixel-value.html
+
+        * rendering/RenderLayer.cpp:
+        (WebCore::RenderLayer::clipToRect):
+
 2014-04-19  Brent Fulgham  <bfulgham@apple.com>
 
         Latched scrolling may interact badly with custom programmatic scrolling

diff --git a/Source/WebCore/rendering/RenderLayer.cpp b/Source/WebCore/rendering/RenderLayer.cpp
@@ -3630,9 +3630,10 @@ static bool inContainingBlockChain(RenderLayer* startLayer, RenderLayer* endLaye
 void RenderLayer::clipToRect(RenderLayer* rootLayer, GraphicsContext* context, const LayoutRect& paintDirtyRect, const ClipRect& clipRect,
                              BorderRadiusClippingRule rule)
 {
+    float deviceScaleFactor = renderer().document().deviceScaleFactor();
     if (clipRect.rect() != paintDirtyRect || clipRect.hasRadius()) {
         context->save();
-        context->clip(clipRect.rect());
+        context->clip(pixelSnappedForPainting(clipRect.rect(), deviceScaleFactor));
     }
 
     if (!clipRect.hasRadius())
@@ -3645,7 +3646,7 @@ void RenderLayer::clipToRect(RenderLayer* rootLayer, GraphicsContext* context, c
         if (layer->renderer().hasOverflowClip() && layer->renderer().style().hasBorderRadius() && inContainingBlockChain(this, layer)) {
                 LayoutPoint delta;
                 layer->convertToLayerCoords(rootLayer, delta);
-                context->clipRoundedRect(FloatRoundedRect(layer->renderer().style().getRoundedInnerBorderFor(LayoutRect(delta, layer->size()))));
+                context->clipRoundedRect(layer->renderer().style().getRoundedInnerBorderFor(LayoutRect(delta, layer->size())).pixelSnappedRoundedRectForPainting(deviceScaleFactor));
         }
 
         if (layer == rootLayer)