Changeset 143073 in webkit

Timestamp:

Feb 15, 2013 5:05:20 PM (11 years ago)

Author:

Simon Fraser

Message:

Constrain fixed layers to the viewport, not the document
​https://bugs.webkit.org/show_bug.cgi?id=109646

Source/WebCore:

Reviewed by Beth Dakin.

It's bad to constrain position:fixed compositing layers to the
document rect, because their bounds will change every time the scroll
position changes, and we're not good currently at synchronizing scrolling
thread layer updates with main thread layer updates, so jiggles ensue.

Fix by constraining position:fixed layers to the viewport.

Test: compositing/geometry/limit-layer-bounds-fixed.html

• rendering/RenderLayerBacking.cpp:

(WebCore::RenderLayerBacking::updateCompositedBounds):

LayoutTests:

Reviewed by Beth Dakin.

Test with a big fixed element in a compositing layer.

• compositing/geometry/limit-layer-bounds-fixed-expected.txt: Added.
• compositing/geometry/limit-layer-bounds-fixed.html: Added.

Location:

trunk

Files:

• LayoutTests/ChangeLog (modified) (1 diff)
• LayoutTests/compositing/geometry/limit-layer-bounds-fixed-expected.txt (added)
• LayoutTests/compositing/geometry/limit-layer-bounds-fixed.html (added)
• Source/WebCore/ChangeLog (modified) (1 diff)
• Source/WebCore/rendering/RenderLayerBacking.cpp (modified) (1 diff)

trunk/LayoutTests/ChangeLog

@@ +1 @@
+2013-02-15  Simon Fraser  <simon.fraser@apple.com>
+
+        Constrain fixed layers to the viewport, not the document
+        https://bugs.webkit.org/show_bug.cgi?id=109646
+
+        Reviewed by Beth Dakin.
+        
+        Test with a big fixed element in a compositing layer.
+
+        * compositing/geometry/limit-layer-bounds-fixed-expected.txt: Added.
+        * compositing/geometry/limit-layer-bounds-fixed.html: Added.
+
 2013-02-15  Simon Fraser  <simon.fraser@apple.com>
 

trunk/Source/WebCore/ChangeLog

@@ +1 @@
+2013-02-15  Simon Fraser  <simon.fraser@apple.com>
+
+        Constrain fixed layers to the viewport, not the document
+        https://bugs.webkit.org/show_bug.cgi?id=109646
+
+        Reviewed by Beth Dakin.
+        
+        It's bad to constrain position:fixed compositing layers to the
+        document rect, because their bounds will change every time the scroll
+        position changes, and we're not good currently at synchronizing scrolling
+        thread layer updates with main thread layer updates, so jiggles ensue.
+        
+        Fix by constraining position:fixed layers to the viewport.
+
+        Test: compositing/geometry/limit-layer-bounds-fixed.html
+
+        * rendering/RenderLayerBacking.cpp:
+        (WebCore::RenderLayerBacking::updateCompositedBounds):
+
 2013-02-13  Jer Noble  <jer.noble@apple.com>
 

trunk/Source/WebCore/rendering/RenderLayerBacking.cpp

@@ -406 +406 @@
         RenderLayer* rootLayer = view->layer();
 
-        // Start by clipping to the document's bounds.
-        LayoutRect clippingBounds = view->unscaledDocumentRect();
+        LayoutRect clippingBounds;
+        if (renderer()->style()->position() == FixedPosition && renderer()->container() == view)
+            clippingBounds = view->frameView()->viewportConstrainedVisibleContentRect();
+        else
+            clippingBounds = view->unscaledDocumentRect();
 
         if (m_owningLayer != rootLayer)