[Webkit-unassigned] [Bug 108556] Constrain layers for fixed position elements to the viewport

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=108556


Simon Fraser (smfr) <simon.fraser at apple.com> changed:

           What    |Removed                     |Added
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                 CC|                            |simon.fraser at apple.com




--- Comment #1 from Simon Fraser (smfr) <simon.fraser at apple.com>  2013-01-31 17:42:33 PST ---
Something like this (but it needs to check if the layer really is fixed):

diff --git a/Source/WebCore/rendering/RenderLayerBacking.cpp b/Source/WebCore/rendering/RenderLayerBacking.cpp
index 75fded054ca231b778640df24bfc4eab1f8f54d3..6953fd62ec30313f1e271441ac1a036032c66614 100644
--- a/Source/WebCore/rendering/RenderLayerBacking.cpp
+++ b/Source/WebCore/rendering/RenderLayerBacking.cpp
@@ -407,6 +407,11 @@ void RenderLayerBacking::updateCompositedBounds()

         // Start by clipping to the document's bounds.
         LayoutRect clippingBounds = view->unscaledDocumentRect();
+        
+        if (renderer()->style()->position() == FixedPosition) {
+            LayoutRect viewportRect = view->frameView()->viewportConstrainedVisibleContentRect();
+            clippingBounds.intersect(viewportRect);
+        }

         if (m_owningLayer != rootLayer)
             clippingBounds.intersect(m_owningLayer->backgroundClipRect(RenderLayer::ClipRectsContext(rootLayer, 0, AbsoluteClipRects)).rect()); // FIXME: Incorrect for CSS regions.

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