CSS Scroll Snap - support snapping to nested elements
https://bugs.webkit.org/show_bug.cgi?id=145843
<rdar://problem/21339581>
Reviewed by Darin Adler.
Source/WebCore:
Tested by css3/scroll-snap/nested-elements.html
The Scroll Snap Point implementation was not properly handling nested elements.
This could be resolved by recursively calling 'appendChildSnapOffsets', but this
seemed like an inefficient approach, especially considering how often this method
is called during various scaling and other operations.
Instead, do the following:
(1) Add a new HashSet to RenderView that holds a collection of RenderElements that
have scroll-snap-coordinates.
(2) During RenderElement::styleWillChange, register all elements that have the
scroll-snap-coordinates style with the RenderView.
(3) When performing 'appendChildSnapOffsets', refer to the HashSet of elements, select the
subset of these entries relevant to the current scrolling container, and build up the
set of scroll-snap-coordinates needed for the current scrolling container.
* page/scrolling/AxisScrollSnapOffsets.cpp:
(WebCore::appendChildSnapOffsets): Check the scroll-snap-coordinate RenderElement HashSet
for the RenderView to find all elements that are children of the current scrolling container.
Add the scroll-snap-coordinates for these RenderElements to the current set of snap points.
* rendering/RenderElement.cpp:
(WebCore::findEnclosingScrollableContainer): New helper function.
(WebCore::RenderElement::styleWillChange): If the current element has scroll-snap-coordinate
defined, remember it for later so we can use it with the relevant scrolling container
after layout completes.
(WebCore::RenderElement::willBeRemovedFromTree): Unregister the current element from the
RenderView.
(WebCore::RenderElement::findEnclosingScrollableContainer): Added. Locate the relevant
scrolling container for the current object.
* rendering/RenderElement.h:
* rendering/RenderView.cpp:
(WebCore::Document::registerRenderElementWithScrollSnapCoordinates): Added.
(WebCore::Document::unregisterRenderElementWithScrollSnapCoordinates): Added.
* rendering/RenderView.h:
LayoutTests:
* css3/scroll-snap/nested-elements-expected.txt: Added.
* css3/scroll-snap/nested-elements.html: Added.
* css3/scroll-snap/scroll-snap-offsets-expected.txt: Updated to
account for 50%/50% scroll-snap-coordinates.
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@185606 268f45cc-cd09-0410-ab3c-d52691b4dbfc
12 files changed
