[iOS] scrollIntoViewIfNeeded is not working with scroll-snap points

• Component: Layout and Rendering
• Status: RESOLVED FIXED

[Brent Fulgham]

In Bug 145216, I corrected a problem where programmatic scrolls did not update the scroll snap state.

Unfortunately, I did not recognize that these changes were not sufficient to correct the problem in iOS, because many of the ScrollAnimator methods used on Mac are stubbed out on iOS.

This needs to be corrected so that the iOS ScrollAnimator knows about the current scroll snap offset index, so that its default '0' value doesn't keep getting retrieved by WebCore code and resetting the offset.

It may be that iOS should keep around a ScrollController object so that we can share the axis offset handling code between the two ports.

[Brent Fulgham]

This bug manifests as a scroll area (with snap points), where calling 'scrollIntoViewIfNeeded" causes the right scroll snap region to move into view, only to flash back to the zeroth scroll element.

[Radar WebKit Bug Importer]

<rdar://problem/21081501>

[Brent Fulgham]

Created attachment 255161 [details]
WIP Patch

[Brent Fulgham]

Created attachment 255172 [details]
Patch

[Simon Fraser (smfr)]

Comment on attachment 255172 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=255172&action=review

> Source/WebCore/page/scrolling/ScrollingStateScrollingNode.h:54
> +        HorizontalSnapOffsetIndex,
> +        VerticalSnapOffsetIndex,

Maybe these should have "Current" in the name.

> Source/WebCore/page/scrolling/ScrollingStateScrollingNode.h:115
> +    unsigned m_currentHorizontalSnapPointIndex { 0 };
> +    unsigned m_currentVerticalSnapPointIndex { 0 };

Do we need to distinguish between "not set" and 0?

> Source/WebCore/platform/cocoa/ScrollController.mm:134
>      , m_lastMomentumScrollTimestamp(0)
> +#if ENABLE(RUBBER_BANDING)
>      , m_startTime(0)

Could use C++11 initialization to avoid these.

[Brent Fulgham]

Comment on attachment 255172 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=255172&action=review

>> Source/WebCore/page/scrolling/ScrollingStateScrollingNode.h:54
>> +        VerticalSnapOffsetIndex,
> 
> Maybe these should have "Current" in the name.

I like that better. I'll change to that.

>> Source/WebCore/page/scrolling/ScrollingStateScrollingNode.h:115
>> +    unsigned m_currentVerticalSnapPointIndex { 0 };
> 
> Do we need to distinguish between "not set" and 0?

No. "non set" is indicated by empty snap offset vectors.

>> Source/WebCore/platform/cocoa/ScrollController.mm:134
>>      , m_startTime(0)
> 
> Could use C++11 initialization to avoid these.

Good idea.

[Brent Fulgham]

Committed r185762: <http://trac.webkit.org/changeset/185762>