[Webkit-unassigned] [Bug 276681] New: Contain:size breaks object-fit

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=276681

            Bug ID: 276681
           Summary: Contain:size breaks object-fit
           Product: WebKit
           Version: Safari 17
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: e at ericportis.com
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

Right now, in WebKit, applying contain:size to an element with object-fit:contain effectively disables object-fit:contain.

The CSSWG has resolved that contain:size should only affect the size of the element's box, but not affect the natural aspect-ratio of its contents (which are used by object-fit): https://github.com/w3c/csswg-drafts/issues/10116#issuecomment-2035803916

Use cases:
- Using object-fit along with auto-sizes (this issue blocks https://bugs.webkit.org/show_bug.cgi?id=253143 because of https://html.spec.whatwg.org/multipage/rendering.html#img-contain-size)
- Making an img's box size completely determined from the "outside-in" without distorting it, e.g., in grids: https://codepen.io/eeeps/pen/PorPgvy

While the spec has not been written yet, there are Web Platform Tests for this resolution, which WebKit alone fails:

https://wpt.fyi/results/css/css-images?label=master&product=safari%5Bstable%5D&product=safari%5Bexperimental%5D&product=firefox%5Bstable%5D&product=chrome%5Bstable%5D&aligned&q=object-fit-containsize%20or%20object-fit-containcontain

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