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<div id="msg">
<dl class="meta">
<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/165963">165963</a></dd>
<dt>Author</dt> <dd>zalan@apple.com</dd>
<dt>Date</dt> <dd>2014-03-20 07:20:22 -0700 (Thu, 20 Mar 2014)</dd>
</dl>
<h3>Log Message</h3>
<pre>Subpixel rendering: Nested layers with subpixel accumulation paint to wrong position.
https://bugs.webkit.org/show_bug.cgi?id=130153
Reviewed by Simon Fraser.
Subpixels (fractional device pixels here) can accumulate through nested layers. Subpixels
need to be propagated through the layer tree so that painting coordinates match layout coordinates.
Subpixel accumulation through nesting (absolute positioning, 2x display):
non-compositing case:
(nested boxes) (layout pos) (norm.paint pos) (translate accumulation, subpixel accumulation, final paint pos)
div -> top: 1.3px 1.3px 1.5px 1.5px 0.2px -> snapped 0.0px -> 1.5px
div -> top: 1.3px 2.6px 2.5px 3.0px 0.4px -> snapped 0.5px -> 2.5px
div -> top: 1.3px 3.9px 4.0px 4.5px 0.6px -> snapped 0.5px -> 4.0px
div -> top: 1.3px 5.2px 5.0px 6.0px 0.8px -> snapped 1.0px -> 5.0px
compositing case:
(nested boxes) (layout pos) (norm.paint pos) (device pixel offset + fractional offset, final pos)
div -> top: 1.3px 1.3px 1.5px 1.0px + 0.3px -> snapped -> 1.5px
div -> top: 1.3px 2.6px 2.5px 2.5px + 0.1px -> snapped -> 2.5px
div -> top: 1.3px 3.9px 4.0px 3.5px + 0.4px -> snapped -> 4.0px
div -> top: 1.3px 5.2px 5.0px 5.0px + 0.2px -> snapped -> 5.0px
Source/WebCore:
Tests: compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation.html
fast/layers/hidpi-nested-layers-with-subpixel-accumulation.html
* rendering/RenderLayer.cpp:
(WebCore::RenderLayer::paintLayerByApplyingTransform):
* rendering/RenderLayerBacking.cpp:
(WebCore::RenderLayerBacking::updateGraphicsLayerGeometry):
* rendering/RenderLayerBacking.h:
(WebCore::RenderLayerBacking::devicePixelFractionFromRenderer):
LayoutTests:
* compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation-expected.html: Added.
* compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation.html: Added.
* fast/layers/hidpi-nested-layers-with-subpixel-accumulation-expected.html: Added.
* fast/layers/hidpi-nested-layers-with-subpixel-accumulation.html: Added.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkLayoutTestsChangeLog">trunk/LayoutTests/ChangeLog</a></li>
<li><a href="#trunkLayoutTestsplatformmacwk2TestExpectations">trunk/LayoutTests/platform/mac-wk2/TestExpectations</a></li>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCorerenderingRenderLayercpp">trunk/Source/WebCore/rendering/RenderLayer.cpp</a></li>
<li><a href="#trunkSourceWebCorerenderingRenderLayerBackingcpp">trunk/Source/WebCore/rendering/RenderLayerBacking.cpp</a></li>
<li><a href="#trunkSourceWebCorerenderingRenderLayerBackingh">trunk/Source/WebCore/rendering/RenderLayerBacking.h</a></li>
</ul>
<h3>Added Paths</h3>
<ul>
<li><a href="#trunkLayoutTestscompositinghidpinestedcompositinglayerswithsubpixelaccumulationexpectedhtml">trunk/LayoutTests/compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation-expected.html</a></li>
<li><a href="#trunkLayoutTestscompositinghidpinestedcompositinglayerswithsubpixelaccumulationhtml">trunk/LayoutTests/compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation.html</a></li>
<li><a href="#trunkLayoutTestsfastlayershidpinestedlayerswithsubpixelaccumulationexpectedhtml">trunk/LayoutTests/fast/layers/hidpi-nested-layers-with-subpixel-accumulation-expected.html</a></li>
<li><a href="#trunkLayoutTestsfastlayershidpinestedlayerswithsubpixelaccumulationhtml">trunk/LayoutTests/fast/layers/hidpi-nested-layers-with-subpixel-accumulation.html</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkLayoutTestsChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/LayoutTests/ChangeLog (165962 => 165963)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/ChangeLog 2014-03-20 14:19:00 UTC (rev 165962)
+++ trunk/LayoutTests/ChangeLog 2014-03-20 14:20:22 UTC (rev 165963)
</span><span class="lines">@@ -1,3 +1,33 @@
</span><ins>+2014-03-20 Zalan Bujtas <zalan@apple.com>
+
+ Subpixel rendering: Nested layers with subpixel accumulation paint to wrong position.
+ https://bugs.webkit.org/show_bug.cgi?id=130153
+
+ Reviewed by Simon Fraser.
+
+ Subpixels (fractional device pixels here) can accumulate through nested layers. Subpixels
+ need to be propagated through the layer tree so that painting coordinates match layout coordinates.
+
+ Subpixel accumulation through nesting (absolute positioning, 2x display):
+ non-compositing case:
+ (nested boxes) (layout pos) (norm.paint pos) (translate accumulation, subpixel accumulation, final paint pos)
+ div -> top: 1.3px 1.3px 1.5px 1.5px 0.2px -> snapped 0.0px -> 1.5px
+ div -> top: 1.3px 2.6px 2.5px 3.0px 0.4px -> snapped 0.5px -> 2.5px
+ div -> top: 1.3px 3.9px 4.0px 4.5px 0.6px -> snapped 0.5px -> 4.0px
+ div -> top: 1.3px 5.2px 5.0px 6.0px 0.8px -> snapped 1.0px -> 5.0px
+
+ compositing case:
+ (nested boxes) (layout pos) (norm.paint pos) (device pixel offset + fractional offset, final pos)
+ div -> top: 1.3px 1.3px 1.5px 1.0px + 0.3px -> snapped -> 1.5px
+ div -> top: 1.3px 2.6px 2.5px 2.5px + 0.1px -> snapped -> 2.5px
+ div -> top: 1.3px 3.9px 4.0px 3.5px + 0.4px -> snapped -> 4.0px
+ div -> top: 1.3px 5.2px 5.0px 5.0px + 0.2px -> snapped -> 5.0px
+
+ * compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation-expected.html: Added.
+ * compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation.html: Added.
+ * fast/layers/hidpi-nested-layers-with-subpixel-accumulation-expected.html: Added.
+ * fast/layers/hidpi-nested-layers-with-subpixel-accumulation.html: Added.
+
</ins><span class="cx"> 2014-03-20 Krzysztof Czech <k.czech@samsung.com>
</span><span class="cx">
</span><span class="cx"> Unreviewed EFL gardening
</span></span></pre></div>
<a id="trunkLayoutTestscompositinghidpinestedcompositinglayerswithsubpixelaccumulationexpectedhtml"></a>
<div class="addfile"><h4>Added: trunk/LayoutTests/compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation-expected.html (0 => 165963)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation-expected.html (rev 0)
+++ trunk/LayoutTests/compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation-expected.html 2014-03-20 14:20:22 UTC (rev 165963)
</span><span class="lines">@@ -0,0 +1,37 @@
</span><ins>+<!DOCTYPE html>
+<html>
+<head>
+<title>This tests that nested compositing layers with subpixel accumulation paint to the same position as regular, non-compositing content.</title>
+<style>
+ div {
+ width: 50px;
+ height: 50px;
+ left: 0px;
+ border: 1px solid;
+ position: absolute;
+ }
+</style>
+</head>
+<body>
+<p id="container"></p>
+<script>
+ left = 0;
+ for (i = 0; i < 6; ++i, left+=55.3) {
+ var container = document.getElementById("container");
+ dimension = 50;
+ for (j = 0; j < 10; ++j, dimension+=-4) {
+ var e = document.createElement("div");
+ e.style.top = "1.3px";
+ e.style.width = dimension + "px";
+ e.style.height = dimension + "px";
+ if (j == 0)
+ e.style.left = left + "px";
+ color = (j * 20);
+ e.style.borderColor = "rgb(" + color + ", " + color + ", " + color + ")";
+ container.appendChild(e);
+ container = e;
+ }
+ }
+</script>
+</body>
+</html>
</ins></span></pre></div>
<a id="trunkLayoutTestscompositinghidpinestedcompositinglayerswithsubpixelaccumulationhtml"></a>
<div class="addfile"><h4>Added: trunk/LayoutTests/compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation.html (0 => 165963)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation.html (rev 0)
+++ trunk/LayoutTests/compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation.html 2014-03-20 14:20:22 UTC (rev 165963)
</span><span class="lines">@@ -0,0 +1,38 @@
</span><ins>+<!DOCTYPE html>
+<html>
+<head>
+<title>This tests that nested compositing layers with subpixel accumulation paint to the same position as regular, non-compositing content.</title>
+<style>
+ div {
+ width: 50px;
+ height: 50px;
+ left: 0px;
+ border: 1px solid;
+ position: absolute;
+ -webkit-transform: translateZ(0);
+ }
+</style>
+</head>
+<body>
+<p id="container"></p>
+<script>
+ left = 0;
+ for (i = 0; i < 6; ++i, left+=55.3) {
+ var container = document.getElementById("container");
+ dimension = 50;
+ for (j = 0; j < 10; ++j, dimension+=-4) {
+ var e = document.createElement("div");
+ e.style.top = "1.3px";
+ e.style.width = dimension + "px";
+ e.style.height = dimension + "px";
+ if (j == 0)
+ e.style.left = left + "px";
+ color = (j * 20);
+ e.style.borderColor = "rgb(" + color + ", " + color + ", " + color + ")";
+ container.appendChild(e);
+ container = e;
+ }
+ }
+</script>
+</body>
+</html>
</ins></span></pre></div>
<a id="trunkLayoutTestsfastlayershidpinestedlayerswithsubpixelaccumulationexpectedhtml"></a>
<div class="addfile"><h4>Added: trunk/LayoutTests/fast/layers/hidpi-nested-layers-with-subpixel-accumulation-expected.html (0 => 165963)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/fast/layers/hidpi-nested-layers-with-subpixel-accumulation-expected.html (rev 0)
+++ trunk/LayoutTests/fast/layers/hidpi-nested-layers-with-subpixel-accumulation-expected.html 2014-03-20 14:20:22 UTC (rev 165963)
</span><span class="lines">@@ -0,0 +1,37 @@
</span><ins>+<!DOCTYPE html>
+<html>
+<head>
+<title>This tests that nested non-compositing layers with subpixel accumulation paint to the same position as regular content.</title>
+<style>
+ div {
+ width: 50px;
+ height: 50px;
+ left: 0px;
+ position: absolute;
+ border: 1px solid;
+ }
+</style>
+</head>
+<body>
+<p id="container"></p>
+<script>
+ left = 0;
+ for (i = 0; i < 6; ++i, left+=55.3) {
+ var container = document.getElementById("container");
+ dimension = 50;
+ for (j = 0; j < 10; ++j, dimension+=-4) {
+ var e = document.createElement("div");
+ e.style.top = "1.3px";
+ e.style.width = dimension + "px";
+ e.style.height = dimension + "px";
+ if (j == 0)
+ e.style.left = left + "px";
+ color = (j * 20);
+ e.style.borderColor = "rgb(" + color + ", " + color + ", " + color + ")";
+ container.appendChild(e);
+ container = e;
+ }
+ }
+</script>
+</body>
+</html>
</ins></span></pre></div>
<a id="trunkLayoutTestsfastlayershidpinestedlayerswithsubpixelaccumulationhtml"></a>
<div class="addfile"><h4>Added: trunk/LayoutTests/fast/layers/hidpi-nested-layers-with-subpixel-accumulation.html (0 => 165963)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/fast/layers/hidpi-nested-layers-with-subpixel-accumulation.html (rev 0)
+++ trunk/LayoutTests/fast/layers/hidpi-nested-layers-with-subpixel-accumulation.html 2014-03-20 14:20:22 UTC (rev 165963)
</span><span class="lines">@@ -0,0 +1,38 @@
</span><ins>+<!DOCTYPE html>
+<html>
+<head>
+<title>This tests that nested non-compositing layers with subpixel accumulation paint to the same position as regular content.</title>
+<style>
+ div {
+ width: 50px;
+ height: 50px;
+ left: 0px;
+ position: absolute;
+ -webkit-transform: rotate(0deg);
+ border: 1px solid;
+ }
+</style>
+</head>
+<body>
+<p id="container"></p>
+<script>
+ left = 0;
+ for (i = 0; i < 6; ++i, left+=55.3) {
+ var container = document.getElementById("container");
+ dimension = 50;
+ for (j = 0; j < 10; ++j, dimension+=-4) {
+ var e = document.createElement("div");
+ e.style.top = "1.3px";
+ e.style.width = dimension + "px";
+ e.style.height = dimension + "px";
+ if (j == 0)
+ e.style.left = left + "px";
+ color = (j * 20);
+ e.style.borderColor = "rgb(" + color + ", " + color + ", " + color + ")";
+ container.appendChild(e);
+ container = e;
+ }
+ }
+</script>
+</body>
+</html>
</ins></span></pre></div>
<a id="trunkLayoutTestsplatformmacwk2TestExpectations"></a>
<div class="modfile"><h4>Modified: trunk/LayoutTests/platform/mac-wk2/TestExpectations (165962 => 165963)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/LayoutTests/platform/mac-wk2/TestExpectations 2014-03-20 14:19:00 UTC (rev 165962)
+++ trunk/LayoutTests/platform/mac-wk2/TestExpectations 2014-03-20 14:20:22 UTC (rev 165963)
</span><span class="lines">@@ -318,6 +318,7 @@
</span><span class="cx"> # hidpi subpixel WebKitTestRunner failure. -blurry generated images.
</span><span class="cx"> webkit.org/b/130175 [ MountainLion Debug ] compositing/hidpi-simple-container-layer-on-device-pixel.html [ ImageOnlyFailure ]
</span><span class="cx"> webkit.org/b/130175 [ MountainLion Debug ] compositing/hidpi-transform-with-render-layer-on-fractional-pixel-value.html [ ImageOnlyFailure ]
</span><ins>+webkit.org/b/130175 [ MountainLion Debug ] compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation.html [ ImageOnlyFailure ]
</ins><span class="cx">
</span><span class="cx"> # Only failing on WK1
</span><span class="cx"> webkit.org/b/104104 fast/overflow/scrollbar-click-retains-focus.html [ Pass ]
</span></span></pre></div>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (165962 => 165963)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog 2014-03-20 14:19:00 UTC (rev 165962)
+++ trunk/Source/WebCore/ChangeLog 2014-03-20 14:20:22 UTC (rev 165963)
</span><span class="lines">@@ -1,3 +1,38 @@
</span><ins>+2014-03-20 Zalan Bujtas <zalan@apple.com>
+
+ Subpixel rendering: Nested layers with subpixel accumulation paint to wrong position.
+ https://bugs.webkit.org/show_bug.cgi?id=130153
+
+ Reviewed by Simon Fraser.
+
+ Subpixels (fractional device pixels here) can accumulate through nested layers. Subpixels
+ need to be propagated through the layer tree so that painting coordinates match layout coordinates.
+
+ Subpixel accumulation through nesting (absolute positioning, 2x display):
+ non-compositing case:
+ (nested boxes) (layout pos) (norm.paint pos) (translate accumulation, subpixel accumulation, final paint pos)
+ div -> top: 1.3px 1.3px 1.5px 1.5px 0.2px -> snapped 0.0px -> 1.5px
+ div -> top: 1.3px 2.6px 2.5px 3.0px 0.4px -> snapped 0.5px -> 2.5px
+ div -> top: 1.3px 3.9px 4.0px 4.5px 0.6px -> snapped 0.5px -> 4.0px
+ div -> top: 1.3px 5.2px 5.0px 6.0px 0.8px -> snapped 1.0px -> 5.0px
+
+ compositing case:
+ (nested boxes) (layout pos) (norm.paint pos) (device pixel offset + fractional offset, final pos)
+ div -> top: 1.3px 1.3px 1.5px 1.0px + 0.3px -> snapped -> 1.5px
+ div -> top: 1.3px 2.6px 2.5px 2.5px + 0.1px -> snapped -> 2.5px
+ div -> top: 1.3px 3.9px 4.0px 3.5px + 0.4px -> snapped -> 4.0px
+ div -> top: 1.3px 5.2px 5.0px 5.0px + 0.2px -> snapped -> 5.0px
+
+ Tests: compositing/hidpi-nested-compositing-layers-with-subpixel-accumulation.html
+ fast/layers/hidpi-nested-layers-with-subpixel-accumulation.html
+
+ * rendering/RenderLayer.cpp:
+ (WebCore::RenderLayer::paintLayerByApplyingTransform):
+ * rendering/RenderLayerBacking.cpp:
+ (WebCore::RenderLayerBacking::updateGraphicsLayerGeometry):
+ * rendering/RenderLayerBacking.h:
+ (WebCore::RenderLayerBacking::devicePixelFractionFromRenderer):
+
</ins><span class="cx"> 2014-03-20 Thiago de Barros Lacerda <thiago.lacerda@openbossa.org>
</span><span class="cx">
</span><span class="cx"> [EFL][GTK] Get CMake to find Freetype2 properly
</span></span></pre></div>
<a id="trunkSourceWebCorerenderingRenderLayercpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/rendering/RenderLayer.cpp (165962 => 165963)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/rendering/RenderLayer.cpp 2014-03-20 14:19:00 UTC (rev 165962)
+++ trunk/Source/WebCore/rendering/RenderLayer.cpp 2014-03-20 14:20:22 UTC (rev 165963)
</span><span class="lines">@@ -4167,14 +4167,18 @@
</span><span class="cx"> // This involves subtracting out the position of the layer in our current coordinate space, but preserving
</span><span class="cx"> // the accumulated error for sub-pixel layout.
</span><span class="cx"> float deviceScaleFactor = renderer().document().deviceScaleFactor();
</span><del>- LayoutPoint delta;
- convertToLayerCoords(paintingInfo.rootLayer, delta);
- delta.moveBy(translationOffset);
</del><ins>+ LayoutPoint offsetFromParent;
+ convertToLayerCoords(paintingInfo.rootLayer, offsetFromParent);
+ offsetFromParent.moveBy(translationOffset);
</ins><span class="cx"> TransformationMatrix transform(renderableTransform(paintingInfo.paintBehavior));
</span><del>- FloatPoint roundedDelta = roundedForPainting(delta, deviceScaleFactor);
- transform.translateRight(roundedDelta.x(), roundedDelta.y());
- LayoutSize adjustedSubPixelAccumulation = paintingInfo.subPixelAccumulation + (delta - LayoutPoint(roundedDelta));
-
</del><ins>+ FloatPoint devicePixelSnappeddOffsetFromParent = roundedForPainting(offsetFromParent, deviceScaleFactor);
+ // Translate the graphics context to the snapping position to avoid off-device-pixel positing.
+ transform.translateRight(devicePixelSnappeddOffsetFromParent.x(), devicePixelSnappeddOffsetFromParent.y());
+ // We handle accumulated subpixels through nested layers here. Since the context gets translated to device pixels,
+ // all we need to do is add the delta to the accumulated pixels coming from ancestor layers. With deep nesting of subpixel positioned
+ // boxes, this could grow to a relatively large number, but the translateRight() balances it.
+ FloatSize delta = offsetFromParent - devicePixelSnappeddOffsetFromParent;
+ LayoutSize adjustedSubPixelAccumulation = paintingInfo.subPixelAccumulation + LayoutSize(delta);
</ins><span class="cx"> // Apply the transform.
</span><span class="cx"> GraphicsContextStateSaver stateSaver(*context);
</span><span class="cx"> context->concatCTM(transform.toAffineTransform());
</span></span></pre></div>
<a id="trunkSourceWebCorerenderingRenderLayerBackingcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/rendering/RenderLayerBacking.cpp (165962 => 165963)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/rendering/RenderLayerBacking.cpp 2014-03-20 14:19:00 UTC (rev 165962)
+++ trunk/Source/WebCore/rendering/RenderLayerBacking.cpp 2014-03-20 14:20:22 UTC (rev 165963)
</span><span class="lines">@@ -739,6 +739,8 @@
</span><span class="cx">
</span><span class="cx"> LayoutPoint offsetFromParent;
</span><span class="cx"> m_owningLayer.convertToLayerCoords(compAncestor, offsetFromParent, RenderLayer::AdjustForColumns);
</span><ins>+ // Device pixel fractions get accumulated through ancestor layers. Our painting offset is layout offset + parent's painting offset.
+ offsetFromParent = offsetFromParent + (compAncestor ? compAncestor->backing()->devicePixelFractionFromRenderer() : LayoutSize());
</ins><span class="cx"> relativeCompositingBounds.moveBy(offsetFromParent);
</span><span class="cx">
</span><span class="cx"> LayoutRect enclosingRelativeCompositingBounds = LayoutRect(enclosingRectForPainting(relativeCompositingBounds, deviceScaleFactor));
</span></span></pre></div>
<a id="trunkSourceWebCorerenderingRenderLayerBackingh"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/rendering/RenderLayerBacking.h (165962 => 165963)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/rendering/RenderLayerBacking.h 2014-03-20 14:19:00 UTC (rev 165962)
+++ trunk/Source/WebCore/rendering/RenderLayerBacking.h 2014-03-20 14:20:22 UTC (rev 165963)
</span><span class="lines">@@ -215,6 +215,8 @@
</span><span class="cx"> void setBlendMode(BlendMode);
</span><span class="cx"> #endif
</span><span class="cx">
</span><ins>+ LayoutSize devicePixelFractionFromRenderer() const { return m_devicePixelFractionFromRenderer; }
+
</ins><span class="cx"> private:
</span><span class="cx"> FloatRect backgroundBoxForPainting() const;
</span><span class="cx">
</span></span></pre>
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