Title: [260828] trunk
- Revision
- 260828
- Author
- [email protected]
- Date
- 2020-04-28 09:05:36 -0700 (Tue, 28 Apr 2020)
Log Message
msn.com: Header flickers when scrolling articles
https://bugs.webkit.org/show_bug.cgi?id=211126
<rdar://problem/56439177>
Reviewed by Simon Fraser.
Source/WebCore:
Test: compositing/fixed-with-clip-stability.html
In case of fixed positioned elements the decision to create backing depends on clip rect.
However RenderLayer::localClipRect() tests for backing in call to clippingRootForPainting(). This creates
instability since clipping depends on backing decision, and backing decision depends on clipping.
* rendering/RenderLayer.cpp:
(WebCore::RenderLayer::localClipRect const):
Specifically the result of clipExceedsBounds test here is affected by computed offsetFromRoot:
"clipRect.contains(cssClipRect)" test fails for zero sized clips with different offsets.
Compute clipExceedsBounds by looking at the clip sizes only and ignoring the position (which should match).
LayoutTests:
* compositing/fixed-with-clip-stability-expected.txt: Added.
* compositing/fixed-with-clip-stability.html: Added.
Modified Paths
Added Paths
Diff
Modified: trunk/LayoutTests/ChangeLog (260827 => 260828)
--- trunk/LayoutTests/ChangeLog 2020-04-28 15:25:11 UTC (rev 260827)
+++ trunk/LayoutTests/ChangeLog 2020-04-28 16:05:36 UTC (rev 260828)
@@ -1,3 +1,14 @@
+2020-04-28 Antti Koivisto <[email protected]>
+
+ msn.com: Header flickers when scrolling articles
+ https://bugs.webkit.org/show_bug.cgi?id=211126
+ <rdar://problem/56439177>
+
+ Reviewed by Simon Fraser.
+
+ * compositing/fixed-with-clip-stability-expected.txt: Added.
+ * compositing/fixed-with-clip-stability.html: Added.
+
2020-04-28 Jason Lawrence <[email protected]>
[ Mac wk2 ] tiled-drawing/scrolling/scroll-snap/scroll-snap-mandatory-padding.html is flaky failing.
Added: trunk/LayoutTests/compositing/fixed-with-clip-stability-expected.txt (0 => 260828)
--- trunk/LayoutTests/compositing/fixed-with-clip-stability-expected.txt (rev 0)
+++ trunk/LayoutTests/compositing/fixed-with-clip-stability-expected.txt 2020-04-28 16:05:36 UTC (rev 260828)
@@ -0,0 +1,2 @@
+text
+PASS
Added: trunk/LayoutTests/compositing/fixed-with-clip-stability.html (0 => 260828)
--- trunk/LayoutTests/compositing/fixed-with-clip-stability.html (rev 0)
+++ trunk/LayoutTests/compositing/fixed-with-clip-stability.html 2020-04-28 16:05:36 UTC (rev 260828)
@@ -0,0 +1,21 @@
+<style>
+body { height: 10000px; }
+.fixed { position:fixed; background-color: green; width: 200px; height:200px; left: 100px;}
+.clipped-fixed { position: fixed; top: 50px; left: 40px; width: 200px; height:20px; clip:rect(0,0,0,0)}
+</style>
+<div class=fixed><div class=clipped-fixed>text</div></div>
+<pre id=results></pre>
+<script>
+if (window.internals) {
+ testRunner.dumpAsText();
+
+ const result1 = internals.layerTreeAsText(document);
+ document.querySelector('.fixed').style.color = "blue";
+ const result2 = internals.layerTreeAsText(document);
+
+ const pass = result1 == result2;
+ results.textContent = pass ? "PASS" : "FAIL";
+ if (!pass)
+ results.textContent += "\n" + result1 + "\n" + result2;
+}
+</script>
Modified: trunk/Source/WebCore/ChangeLog (260827 => 260828)
--- trunk/Source/WebCore/ChangeLog 2020-04-28 15:25:11 UTC (rev 260827)
+++ trunk/Source/WebCore/ChangeLog 2020-04-28 16:05:36 UTC (rev 260828)
@@ -1,3 +1,25 @@
+2020-04-28 Antti Koivisto <[email protected]>
+
+ msn.com: Header flickers when scrolling articles
+ https://bugs.webkit.org/show_bug.cgi?id=211126
+ <rdar://problem/56439177>
+
+ Reviewed by Simon Fraser.
+
+ Test: compositing/fixed-with-clip-stability.html
+
+ In case of fixed positioned elements the decision to create backing depends on clip rect.
+ However RenderLayer::localClipRect() tests for backing in call to clippingRootForPainting(). This creates
+ instability since clipping depends on backing decision, and backing decision depends on clipping.
+
+ * rendering/RenderLayer.cpp:
+ (WebCore::RenderLayer::localClipRect const):
+
+ Specifically the result of clipExceedsBounds test here is affected by computed offsetFromRoot:
+ "clipRect.contains(cssClipRect)" test fails for zero sized clips with different offsets.
+
+ Compute clipExceedsBounds by looking at the clip sizes only and ignoring the position (which should match).
+
2020-04-28 Zalan Bujtas <[email protected]>
[LFC] Introduce FormattingContext::ConstraintsForOutOfFlowContent
Modified: trunk/Source/WebCore/rendering/RenderLayer.cpp (260827 => 260828)
--- trunk/Source/WebCore/rendering/RenderLayer.cpp 2020-04-28 15:25:11 UTC (rev 260827)
+++ trunk/Source/WebCore/rendering/RenderLayer.cpp 2020-04-28 16:05:36 UTC (rev 260828)
@@ -5978,8 +5978,8 @@
if (renderer().hasClip()) {
// CSS clip may be larger than our border box.
- LayoutRect cssClipRect = downcast<RenderBox>(renderer()).clipRect(toLayoutPoint(offsetFromRoot), nullptr);
- clipExceedsBounds = !clipRect.contains(cssClipRect);
+ LayoutRect cssClipRect = downcast<RenderBox>(renderer()).clipRect({ }, nullptr);
+ clipExceedsBounds = !cssClipRect.isEmpty() && (clipRect.width() < cssClipRect.width() || clipRect.height() < cssClipRect.height());
}
clipRect.move(-offsetFromRoot);
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