commit | e4b78613c5152a38fe6712643dcbe7582591427f | [log] [tgz] |
---|---|---|
author | Alison Maher <almaher@microsoft.com> | Thu Oct 21 00:40:31 2021 |
committer | Blink WPT Bot <blink-w3c-test-autoroller@chromium.org> | Thu Oct 21 00:47:51 2021 |
tree | 1ee35a34ede1a8f0f46552ab66ba0416c47f7f2b | |
parent | efd81ed08a5f126111abfa870361637b0676f1b0 [diff] |
[FlexNG] Initial set-up for single-line column flex fragmentation Spec: https://drafts.csswg.org/css-flexbox-1/#pagination There are four different algorithms for fragmenting flex items depending on the type of container. The first of which I will be focusing on is fragmentation for a single-line column flex container since it will be most similar to normal block fragmentation. Because we need to know the item location before fragmenting, an additional layout pass was added to NGFlexLayoutAlgorithm:: GiveLinesAndItemsFinalPositionAndSize() to take fragmentation into account, at which point we know the final block offset of the item. The looping mechanism in this method was replaced by a newly added NGFlexItemIterator, which will iterate over items with break tokens first, and continue from sibling items thereafter. The code to set up the constraint space for item layout in BuildSpaceForLayout() was updated with an additional call to SetupSpaceBuilderForFragmentation() in the final fragmentation layout pass. Because we re-layout the entire flex container on every pass, and then perform a final layout pass taking fragmentation into account, a new bool was added to the constraint space's RareData to keep track of when to avoid caching. We want to avoid caching the initial (non-fragmenting) layout pass - this prevents the fragmented results from getting overridden each time. There may be potential to avoid this if we can store this information between fragmentainers, or if we cache it in a new slot type instead of not caching at all. With this CL, we can now support fragmentation for a single item in a single-line column flex container that spans several fragmentainers. In order to support multiple fragmented sibling items, additional work will need to be done - including proper block offset calculation, intrinsic block size calculation, and handling of a break before, all of which have TODOs. Some other interesting open questions and areas of investigation include (TODOs included in the code for these, as well): - How will the devtools logic work when items have multiple fragments? - An additional layout pass is already made for items that stretch via ApplyStretchAlignmentToChild(). It would be optimal if we could make use of this layout pass to apply fragmentation, as well, to avoid yet another layout pass in this case. - How to handle flexbox writing mode roots? They are currently treated as monolithic. Bug: 660611 Change-Id: I35bcf407bbf741bb5df71f2acc70767be74090c0 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3212348 Reviewed-by: David Grogan <dgrogan@chromium.org> Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org> Reviewed-by: Morten Stenshorne <mstensho@chromium.org> Commit-Queue: Alison Maher <almaher@microsoft.com> Cr-Commit-Position: refs/heads/main@{#933725}
The web-platform-tests Project is a cross-browser test suite for the Web-platform stack. Writing tests in a way that allows them to be run in all browsers gives browser projects confidence that they are shipping software that is compatible with other implementations, and that later implementations will be compatible with their implementations. This in turn gives Web authors/developers confidence that they can actually rely on the Web platform to deliver on the promise of working across browsers and devices without needing extra layers of abstraction to paper over the gaps left by specification editors and implementors.
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