[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 10:47:29 PDT 2011

Hi Anders,

At this point in time, we see no reason to allow for non-zero padding in
overflow:scroll regions because you can always just move the page into a
unobstructed area and then scroll through that overflow region.



On Thu, Oct 6, 2011 at 1:43 PM, Anders Carlsson <andersca at apple.com> wrote:

> Do you envision this being useful on overflow:scroll regions as well or is
> it just frames? If it's just frames, then it seems like something we could
> keep in ScrollView? (I haven't looked at the patch yet).
> - Anders
> On Oct 6, 2011, at 10:41 AM, Fady Samuel wrote:
> Hi Anders,
> Thanks for your reply.
> Yes, you are correct. This padding would be between the content and the
> overhang area.
> Thanks,
> Fady
> 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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>> webkit-dev at lists.webkit.org
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