[webkit-dev] Adding "Scroll Padding" to allow scroll beyond the edge of the page (within some bounds)

Anders Carlsson andersca at apple.com
Thu Oct 6 10:32:16 PDT 2011

Hi Fady,

so if I'm understanding correctly, in the context of rubber-band scrolling, this padding would be between the content and the overhang area?

As far as constrainsScrollingToContentEdge goes, I'd like to get rid of it and just have two scroll functions, one that constrains to the content edge and one that doesn't.

- Anders

On Oct 6, 2011, at 10:03 AM, Fady Samuel wrote:

> Hi all,
> We'd like to provide a general mechanism in WebKit for embedders to scroll page content so that it is not hidden by embedder-provided UI elements that overlap the page. 
> In some cases, if a floating UI element overlaps the edge of the page, we'd like to allow the embedder to scroll beyond the edge of the page to allow the hidden content to move to an area that isn't overlapped by UI elements. This feature is orthogonal to rubber band scrolling.
> One approach we considered taking is to allow the platform to set "scroll padding" to a FrameView/ScrollableArea to allow scrolling beyond the edge of the page. 
> As a more concrete example, one can imagine a persistent Chromium extension that floats above the edge of the page. A link may lie behind the floating window.  That link would be inaccessible unless the page is allowed to scroll beyond its edge. 
> An experimental and incomplete implementation of this idea can be found here: https://bugs.webkit.org/show_bug.cgi?id=68184
> After some additional consideration since this patch was posted, I don't believe scroll padding should interact with ScrollView::constrainsScrollingToContentEdge the way it does in the patch. Instead, I feel that scroll padding should be ignored if constrainsScrollingToContentEdge is false. That way rubber band scrolling is not affected at all by this.
> What are your thoughts and suggestions? Is this feature sufficiently general to be implemented in WebCore? What are your thoughts about its interaction with ScrollView::constrainsScrollingToContentEdge?
> Thanks,
> Fady
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