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

Fady Samuel fsamuel at chromium.org
Thu Oct 6 10:41:12 PDT 2011

Hi Anders,

Thanks for your reply.

Yes, you are correct. This padding would be between the content and the
overhang area.



On Thu, Oct 6, 2011 at 1:32 PM, Anders Carlsson <andersca at apple.com> wrote:

> 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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