W3C home > Mailing lists > Public > www-style@w3.org > July 2015

Re: [css-snappoints] Feedback roll-up

From: Robert O'Callahan <robert@ocallahan.org>
Date: Fri, 3 Jul 2015 18:27:39 +1200
Message-ID: <CAOp6jLZ=PQ2x1WUQFs2ag0U_2iBQ3wRCVpZG9XWkTa4oU7EYqg@mail.gmail.com>
To: Majid Valipour <majidvp@chromium.org>
Cc: Matt Rakow <marakow@microsoft.com>, "www-style@w3.org" <www-style@w3.org>, Simon Fraser <smfr@me.com>, "bfulgham@apple.com" <bfulgham@apple.com>
On Fri, Jul 3, 2015 at 3:07 AM, Majid Valipour <majidvp@chromium.org> wrote:

> I would argue that there should be a way for programmatic scrolling to
> evade "snap-points" when necessary. Perhaps evading snap points should be
> default for programmatic scrolls with an option to opt in to snap points!
> When an application uses a programmatic scrolls to scroll to a specific
> offset it actually means to scroll to that offset and snap points should
> not interfere with that. (Element.scrollIntoView and focus are the only
> exceptions IMO)
>
> Changing this behavior breaks long-standing developer expectations of
> setting scroll offsets and it taking effect (See example below). It also
> prevents some legitimate usecase such as animating scroll offsets.
>

I agree.

However, that conflicts with the spec text "If the content changes such
that the visual viewport would no longer rest on a snap point (e.g. content
is added, moved, deleted, resized), the scroll offset must be modified to
maintain this guarantee." It doesn't make sense to allow some DOM APIs to
violate that invariant but require other content changes to preserve it. If
a script scrolls away from a snappoint, and then there's an insignificant
DOM change, what would we do? I suggest we just remove that spec
requirement; I think it's hard to implement and is likely to produce
undesirable behavior anyway.

Rob
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Received on Friday, 3 July 2015 06:33:44 UTC

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