Bug 176454 - Implement CSS overscroll-behavior
Summary: Implement CSS overscroll-behavior
Status: NEW
Alias: None
Product: WebKit
Classification: Unclassified
Component: CSS (show other bugs)
Version: WebKit Nightly Build
Hardware: Unspecified Unspecified
: P2 Normal
Assignee: Frédéric Wang (:fredw)
URL: https://drafts.csswg.org/css-overscro...
Keywords: InRadar
: 179266 (view as bug list)
Depends on: 192358 192397
  Show dependency treegraph
Reported: 2017-09-06 07:13 PDT by Majid Valipour
Modified: 2019-07-25 10:23 PDT (History)
27 users (show)

See Also:

Testcase (2.70 KB, text/html)
2018-09-10 08:07 PDT, Frédéric Wang (:fredw)
no flags Details
WIP Patch (CSS parsing only) (67.14 KB, patch)
2018-09-10 08:07 PDT, Frédéric Wang (:fredw)
no flags Details | Formatted Diff | Diff
WIP Patch (CSS parsing only) (16.18 KB, patch)
2018-09-26 07:55 PDT, Frédéric Wang (:fredw)
no flags Details | Formatted Diff | Diff
Testcase of annoying scroll chaining (630 bytes, text/html)
2018-10-31 04:32 PDT, Frédéric Wang (:fredw)
no flags Details
WIP Patch (CSS parsing and preference option) (26.17 KB, patch)
2018-11-15 05:23 PST, Frédéric Wang (:fredw)
no flags Details | Formatted Diff | Diff
WIP Patch (33.37 KB, patch)
2018-11-27 07:43 PST, Frédéric Wang (:fredw)
no flags Details | Formatted Diff | Diff
WIP Patch (33.37 KB, patch)
2018-11-28 10:21 PST, Frédéric Wang (:fredw)
no flags Details | Formatted Diff | Diff
WIP Patch (33.58 KB, patch)
2018-11-28 10:32 PST, Frédéric Wang (:fredw)
no flags Details | Formatted Diff | Diff
Add overscroll behavior property to scrolling tree (7.64 KB, patch)
2018-11-29 07:59 PST, Frédéric Wang (:fredw)
no flags Details | Formatted Diff | Diff
WIP Patch (53.63 KB, patch)
2018-12-03 14:50 PST, Frédéric Wang (:fredw)
no flags Details | Formatted Diff | Diff
Patch (53.88 KB, patch)
2018-12-04 03:18 PST, Frédéric Wang (:fredw)
no flags Details | Formatted Diff | Diff
Patch (applies on top of bug 192358) (52.88 KB, patch)
2018-12-04 09:16 PST, Frédéric Wang (:fredw)
no flags Details | Formatted Diff | Diff
tentative rebase (not tested) (52.06 KB, patch)
2019-02-27 09:20 PST, Frédéric Wang (:fredw)
no flags Details | Formatted Diff | Diff

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Description Majid Valipour 2017-09-06 07:13:08 PDT
Consider implementing the new CSS scroll-boundary-behavior property.

## Specification
This feature specification is being incubated in WICG: 

Note that this is first CSSWG spec which is going through this new process). 

Additional background on this feature may be found here: 

## Summary
CSS scroll-boundary-behavior standardizes a supercharged version of "-ms-scroll-chaining". It
allows developers to determine the browser's behavior once a scroller has reached its full extent.
The unused delta can be propagated to the parent causing scroll chaining, create a glow/bounce
effect without chaining, or just get consumed silently. In particular when used on viewport
defining element, it controls if overscroll can be used for navigation actions such as pull-to-
refresh or swipe navigation.

scroll-boundary-behavior: auto | contain | none

  * `auto`: propagate scroll to the parent scroller. If there is no parent scroller (e.g.,
    viewport) user-agent may perform a default action (e.g. navigation) or show any appropriate
    overscroll UI affordance. This is the default value.
  * `contain`: do not propagate. The user agent may show an appropriate overscroll UI affordance
    such as bounce or glow.
  * `none`: same as contain but also prevents any overscroll UI affordance e.g. bounce or glow.

There will be scroll-boundary-behavior-{x,y} long-hands to control each axis individually.

## Current State
The specification and API has received positive feedback and support from EdgeHTML [1], Mozilla
[2], Chromium[3], and web developers [4,5]. We at Chromium have an implementation landed in
Canary (behind a feature flag**). If we don't receive any strong negative signal we plan to ship
in M63 per intent-to-ship. [3]

[1] https://github.com/w3c/csswg-drafts/issues/769#issuecomment-270228948
[2] https://bugzilla.mozilla.org/show_bug.cgi?id=951793#c11
[3] https://groups.google.com/a/chromium.org/d/msg/blink-dev/OqBNF2efmFA/3ByBUKyaCgAJ
[4] https://github.com/w3c/csswg-drafts/issues/769#issuecomment-279832555
[5] https://github.com/w3c/csswg-drafts/issues/769#issuecomment-288878908

** --enable-web-platform-experimental-features or --enable-blink-features=CSSScrollBoundaryBehavior
Comment 1 Radar WebKit Bug Importer 2017-09-07 13:56:45 PDT
Comment 2 Benoit Girard 2017-11-22 10:29:26 PST
The property has been renamed to 'overscroll-behavior': https://github.com/WICG/overscroll-behavior

There's been no major changes otherwise.
Comment 3 Simon Fraser (smfr) 2017-12-07 10:45:20 PST
*** Bug 179266 has been marked as a duplicate of this bug. ***
Comment 4 Frédéric Wang (:fredw) 2018-09-10 08:07:08 PDT
Created attachment 349309 [details]
Comment 5 Frédéric Wang (:fredw) 2018-09-10 08:07:48 PDT
Created attachment 349310 [details]
WIP Patch (CSS parsing only)
Comment 6 Frédéric Wang (:fredw) 2018-09-26 07:55:08 PDT
Created attachment 350862 [details]
WIP Patch (CSS parsing only)

Use runtime instead of compile time flag
Comment 7 Frédéric Wang (:fredw) 2018-10-31 04:32:04 PDT
Created attachment 353488 [details]
Testcase of annoying scroll chaining

This is a simple use case showing when scroll chaining can be annoying. If you scroll the overflow node to its maximum limit, release it and try to scroll it any further then the scrolling is propagated to the main frame (expected scroll chaining behavior). Then if you don't wait a bit but scroll immediately the overflow node again in the other direction, then the scrolling still applies to the main frame. The "position: fixed" is not essential here, but it can make things even more confusing since one does not see the overflow node moving when the main frame is scrolled.
Comment 8 Frédéric Wang (:fredw) 2018-11-15 05:23:57 PST
Created attachment 354920 [details]
WIP Patch (CSS parsing and preference option)
Comment 9 Frédéric Wang (:fredw) 2018-11-27 07:43:54 PST
Created attachment 355733 [details]
WIP Patch
Comment 10 Frédéric Wang (:fredw) 2018-11-28 10:21:11 PST
Created attachment 355887 [details]
WIP Patch

Just some minor change with respect to the 355733, so that "non-local boundary default actions" (e.g. scroll chaining or navigation) are now blocked for overscroll-behavior: none or contain. For now this works on macOS and GTK on attachment 349309 [details] but iOS uses a different code path.
Comment 11 Frédéric Wang (:fredw) 2018-11-28 10:32:19 PST
Created attachment 355888 [details]
WIP Patch

Sorry, I uploaded the wrong patch. Here is the correct one. Also I forgot to say that this only blocks scrolling via the mouse, not via the keyboard (my chromium release on Linux seems to have the same behavior).
Comment 12 Frédéric Wang (:fredw) 2018-11-29 07:59:53 PST
Created attachment 356006 [details]
Add overscroll behavior property to scrolling tree
Comment 13 Frédéric Wang (:fredw) 2018-12-03 14:50:11 PST
Created attachment 356410 [details]
WIP Patch

@smfr: I tried to experiment with UIScrollView's bounces/alwaysBounceHorizontal/alwaysBounceVertical but unfortunately it does not seem possible to use them to disable/enable bouncing in independent directions. I don't see any straightforward UIScrollView API to disable scroll chaining. I guess UIScrollView should probably have an overscroll property none/contain/auto so that it is possible to enable/disable things like bouncing or scrolling chaining (more generally local and non-local boundary default actions) via the UIKitSPI. I understand this is proprietary code and hence has to be handled by Apple, right? If so, can you please comment on rdar://problem/34315997 ?

This patch passes the horizontal/vertical overscroll behavior to the UI process, but probably it would be cleaner to move the OverscrollBehavior enum in ScrollTypes.h
Comment 14 Frédéric Wang (:fredw) 2018-12-04 03:18:25 PST
Created attachment 356479 [details]
Comment 15 Frédéric Wang (:fredw) 2018-12-04 09:16:44 PST
Created attachment 356505 [details]
Patch (applies on top of bug 192358)
Comment 16 Frédéric Wang (:fredw) 2018-12-06 01:23:56 PST
There is a WPT manual test at https://w3c-test.org/css/css-overscroll-behavior/overscrollBehavior-manual.html
Comment 17 jonjohnjohnson 2018-12-10 13:57:50 PST
Definitely know I'm being a sort of busy body, but sincerely wondering if the webkit implementation of `overscroll-behavior` using the `contain` (or even `none`) value will allow for the same scroll containment in iOS that is showcased in in the following quite complex and hacked link:


Meaning, we won't have to resort to such a mess to get this user experience?
Comment 18 Ben Frain 2019-02-12 08:27:50 PST
Really hope this is implemented soon. Any modal on iOS that has scrolling inside suffers terribly currently. Having this would mean an end to toggling overflow hidden every time we want a modal with scrollable content.
Comment 19 Henrik Joreteg 2019-02-21 06:16:02 PST
This is big deal for anybody who's implementing any sort of slide-in "hamburger" menu, etc.

For example, I'm currently working with one of the largest retailers in the world on a UI that involves a shopping cart that slides in from the right so you can quickly see cart contents without leaving your shopping experience.

As you add things to your cart that list will grow to the point where it needs to be scrolled. It's obviously not desirable to scroll the underlying page. 

What amounts to being a simple CSS rule in most browsers currently requires frustrating hacks to get it to working correctly on iOS.

Closely related... the additional requirement for adding '-webkit-overflow-scrolling: touch' is another weird one. I can't imagine a scenario where I'm wanting something to on the page to be scrollable but where I *don't* want momentum scrolling. Frankly, scrolling something without this behavior feels super broken. Seems to me it should just be the default.

Anyway, these scrolling-related issues happen increasingly as developers build more complex web pages and currently, it's one of those things that make developers curse Apple.

I think getting this resolved would buy a lot of goodwill.

Please consider implementing this. Thanks!
Comment 20 Frédéric Wang (:fredw) 2019-02-27 09:20:01 PST
Created attachment 363094 [details]
tentative rebase (not tested)
Comment 21 Dmitry Semenov 2019-04-15 10:58:16 PDT
Would be great if this also allowed to prevent edge swipe to go back gesture.

This would help with horizontal carousels. Users often want to swipe carousel, but swipe to "the previous page" instead. The majority of e-commerce websites use a carousel on the product page.

At least for those that use "native" horizontal scroll with `-webkit-overflow-scrolling: touch`.
Comment 22 jonjohnjohnson 2019-04-15 11:51:03 PDT
(In reply to Dmitry Semenov from comment #21)

As far as...
> This would help with horizontal carousels.
I believe spec has you covered, in that internal horizontal scrolling can be made to never chain out to the native viewport behavior with values `none`/`contain`. 

But for this general case...
> Would be great if this also allowed to prevent edge swipe to go back gesture.
Sadly, I think the current spec covers this general case only if your website already has the viewport horizontally scrolling. See https://github.com/w3c/csswg-drafts/issues/3349

- https://developers.google.com/web/updates/2017/11/overscroll-behavior
- https://drafts.csswg.org/css-overscroll-behavior-1/
Comment 23 jonjohnjohnson 2019-04-19 07:57:42 PDT
(In reply to Frédéric Wang (:fredw))

Beware of https://bugs.chromium.org/p/chromium/issues/detail?id=954423 when implementing this on the viewport scroller. Considering css compat with regards to html/body propagation of this property.
Comment 24 Frédéric Wang (:fredw) 2019-06-28 04:06:44 PDT
It seems there are discussions elsewhere to introduce flow-relative properties:


I personally think it makes sense.