Bug 142552 – scroll-snap-destination and scroll-snap-coordinate do not seem to work together properly

• Status: RESOLVED
• Resolution: FIXED
• Component: Layout and Rendering

[Brent Fulgham]

Created attachment 248372 [details]
Example (manual) failing test case

The "scroll-snap-destination" property is used to specify a location in the scrolling container's viewport that should be used for snapping. The "scroll-snap-coordinate" property is used to specify the coordinate in each of the child elements to align with the "scroll-snap-destination" location.

This does not seem to work properly at present.

[Radar WebKit Bug Importer]

<rdar://problem/20114743>

[Brent Fulgham]

Created attachment 249215 [details]
Patch

[Brent Fulgham]

There were the following problems:

1. During testing I encountered at least one case where the CSSParser handed me a scroll-snap-destination with more than two components. I am no longer able to reproduce this, but I have added an assertion to try to catch this in the future.

2. We were not always putting a '0' offset snap point, which prevented us from snap scrolling to the beginning of the scroll container. This had the effect of creating a weird "drift" effect where WebKit tried to pull you away from the left edge of content towards the first snap point.

3. When using scroll-snap-destination/scroll-snap-coordinate markup, we were not generate per-element snap offsets to use as the basis for the "-destination" and "-coordinate" values to adjust.

[Dean Jackson]

Comment on attachment 249215 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=249215&action=review

> Source/WebCore/page/scrolling/AxisScrollSnapOffsets.cpp:103
> +            // Only add zero at the beginning

Nit: Missing full stop.

[Brent Fulgham]

Committed r181855: <http://trac.webkit.org/changeset/181855>

[Simon Fraser (smfr)]

Comment on attachment 249215 [details]
Patch

Why no tests?