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<dl class="meta">
<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/185916">185916</a></dd>
<dt>Author</dt> <dd>zalan@apple.com</dd>
<dt>Date</dt> <dd>2015-06-24 10:53:44 -0700 (Wed, 24 Jun 2015)</dd>
</dl>
<h3>Log Message</h3>
<pre>Subpixel rendering: roundToDevicePixel() snaps to wrong value.
https://bugs.webkit.org/show_bug.cgi?id=146273
rdar://problem/18509840
Reviewed by Simon Fraser.
Due to the floating point approximate representation, we can't always produce
the correct snap value. This patch addresses the issue by removing redundant kFixedPointDenominator multiplication
and by changing the rounding in roundToDevicePixel() from float to double.
Source/WebCore:
API test is added.
* platform/LayoutUnit.h:
(WebCore::roundToDevicePixel):
Tools:
* TestWebKitAPI/Tests/WebCore/LayoutUnit.cpp:
(TestWebKitAPI::TEST):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCoreplatformLayoutUnith">trunk/Source/WebCore/platform/LayoutUnit.h</a></li>
<li><a href="#trunkToolsChangeLog">trunk/Tools/ChangeLog</a></li>
<li><a href="#trunkToolsTestWebKitAPITestsWebCoreLayoutUnitcpp">trunk/Tools/TestWebKitAPI/Tests/WebCore/LayoutUnit.cpp</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (185915 => 185916)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog 2015-06-24 16:57:30 UTC (rev 185915)
+++ trunk/Source/WebCore/ChangeLog 2015-06-24 17:53:44 UTC (rev 185916)
</span><span class="lines">@@ -1,3 +1,20 @@
</span><ins>+2015-06-24 Zalan Bujtas <zalan@apple.com>
+
+ Subpixel rendering: roundToDevicePixel() snaps to wrong value.
+ https://bugs.webkit.org/show_bug.cgi?id=146273
+ rdar://problem/18509840
+
+ Reviewed by Simon Fraser.
+
+ Due to the floating point approximate representation, we can't always produce
+ the correct snap value. This patch addresses the issue by removing redundant kFixedPointDenominator multiplication
+ and by changing the rounding in roundToDevicePixel() from float to double.
+
+ API test is added.
+
+ * platform/LayoutUnit.h:
+ (WebCore::roundToDevicePixel):
+
</ins><span class="cx"> 2015-06-23 Matt Rajca <mrajca@apple.com>
</span><span class="cx">
</span><span class="cx"> MediaSession: Support setting of metadata
</span></span></pre></div>
<a id="trunkSourceWebCoreplatformLayoutUnith"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/platform/LayoutUnit.h (185915 => 185916)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/platform/LayoutUnit.h 2015-06-24 16:57:30 UTC (rev 185915)
+++ trunk/Source/WebCore/platform/LayoutUnit.h 2015-06-24 17:53:44 UTC (rev 185916)
</span><span class="lines">@@ -874,16 +874,18 @@
</span><span class="cx">
</span><span class="cx"> inline float roundToDevicePixel(LayoutUnit value, const float pixelSnappingFactor, bool needsDirectionalRounding = false)
</span><span class="cx"> {
</span><del>- auto roundInternal = [&] (float valueToRound) { return roundf((valueToRound * pixelSnappingFactor) / kFixedPointDenominator) / pixelSnappingFactor; };
</del><ins>+ double valueToRound = value.toDouble();
+ if (needsDirectionalRounding)
+ valueToRound -= LayoutUnit::epsilon() / (2 * kFixedPointDenominator);
</ins><span class="cx">
</span><del>- float adjustedValue = value.rawValue() - (needsDirectionalRounding ? LayoutUnit::epsilon() / 2.0f : 0);
- if (adjustedValue >= 0)
- return roundInternal(adjustedValue);
</del><ins>+ if (valueToRound >= 0)
+ return round(valueToRound * pixelSnappingFactor) / pixelSnappingFactor;
</ins><span class="cx">
</span><span class="cx"> // This adjusts directional rounding on negative halfway values. It produces the same direction for both negative and positive values.
</span><ins>+ // Instead of rounding negative halfway cases away from zero, we translate them to positive values before rounding.
</ins><span class="cx"> // It helps snapping relative negative coordinates to the same position as if they were positive absolute coordinates.
</span><del>- float translateOrigin = fabsf(adjustedValue - LayoutUnit::fromPixel(1));
- return roundInternal(adjustedValue + (translateOrigin * kFixedPointDenominator)) - translateOrigin;
</del><ins>+ unsigned translateOrigin = -value.rawValue();
+ return (round((valueToRound + translateOrigin) * pixelSnappingFactor) / pixelSnappingFactor) - translateOrigin;
</ins><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> inline float floorToDevicePixel(LayoutUnit value, float pixelSnappingFactor)
</span></span></pre></div>
<a id="trunkToolsChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Tools/ChangeLog (185915 => 185916)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Tools/ChangeLog 2015-06-24 16:57:30 UTC (rev 185915)
+++ trunk/Tools/ChangeLog 2015-06-24 17:53:44 UTC (rev 185916)
</span><span class="lines">@@ -1,3 +1,18 @@
</span><ins>+2015-06-24 Zalan Bujtas <zalan@apple.com>
+
+ Subpixel rendering: roundToDevicePixel() snaps to wrong value.
+ https://bugs.webkit.org/show_bug.cgi?id=146273
+ rdar://problem/18509840
+
+ Reviewed by Simon Fraser.
+
+ Due to the floating point approximate representation, we can't always produce
+ the correct snap value. This patch addresses the issue by removing redundant kFixedPointDenominator multiplication
+ and by changing the rounding in roundToDevicePixel() from float to double.
+
+ * TestWebKitAPI/Tests/WebCore/LayoutUnit.cpp:
+ (TestWebKitAPI::TEST):
+
</ins><span class="cx"> 2015-06-24 Brady Eidson <beidson@apple.com>
</span><span class="cx">
</span><span class="cx"> Update JavaScript dialog delegates to include a WKSecurityOriginRef argument.
</span></span></pre></div>
<a id="trunkToolsTestWebKitAPITestsWebCoreLayoutUnitcpp"></a>
<div class="modfile"><h4>Modified: trunk/Tools/TestWebKitAPI/Tests/WebCore/LayoutUnit.cpp (185915 => 185916)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Tools/TestWebKitAPI/Tests/WebCore/LayoutUnit.cpp 2015-06-24 16:57:30 UTC (rev 185915)
+++ trunk/Tools/TestWebKitAPI/Tests/WebCore/LayoutUnit.cpp 2015-06-24 17:53:44 UTC (rev 185916)
</span><span class="lines">@@ -231,5 +231,19 @@
</span><span class="cx"> ASSERT_EQ((LayoutUnit(intMinForLayoutUnit) + LayoutUnit(1)).floor(), intMinForLayoutUnit + 1);
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+TEST(WebCoreLayoutUnit, LayoutUnitPixelSnapping)
+{
+ for (int i = -100000; i <= 100000; ++i) {
+ ASSERT_EQ(roundToDevicePixel(LayoutUnit(i), 1), i);
+ ASSERT_EQ(roundToDevicePixel(LayoutUnit(i), 2), i);
+ ASSERT_EQ(roundToDevicePixel(LayoutUnit(i), 3), i);
+ }
</ins><span class="cx">
</span><ins>+ for (float i = -10000; i < 0; i = i + 0.5)
+ ASSERT_FLOAT_EQ(roundToDevicePixel(LayoutUnit(i), 2), i);
+
+ for (float i = -10000.25; i < 0; i = i + 0.5)
+ ASSERT_FLOAT_EQ(roundToDevicePixel(LayoutUnit(i), 2), i + 0.25);
+}
+
</ins><span class="cx"> } // namespace TestWebKitAPI
</span></span></pre>
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