[Webkit-unassigned] [Bug 227615] New: animation-fill-mode does not correctly apply viewport-based units

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=227615

            Bug ID: 227615
           Summary: animation-fill-mode does not correctly apply
                    viewport-based units
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: All
               URL: https://will.harris.ch/tcr-animation-fill-mode.html
                OS: All
            Status: NEW
          Keywords: HasReduction
          Severity: Normal
          Priority: P2
         Component: Animations
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: will-web-webkitbugs at harris.ch
                CC: dino at apple.com, graouts at apple.com

If an animation is applied with an "animation-fill-mode", and the values in the first/last animation frame are expressed using viewport units (vw, vh), the affected element will not be correctly positioned if the viewport is subsequently resized after the animation has ended (e.g. desktop browser when resizing, mobile browser when orientation is changed).

The attached test case reduction shows the issue. It contains three divs, all positioned with viewport units:

- one reference div, unanimated
- one div animated without "animation-fill-mode"
- one div animated with "animation-fill-mode"

The animated divs share the same animation and CSS positioning. The only difference is that the last div's animation also uses a fill mode.

When the browser window is resized, the top two divs move correctly, and remain aligned with a reference marker line. The last div does not move as expected to respect the changed viewport size.

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