[Webkit-unassigned] [Bug 232280] New: Missing 'from' selector on @keyframes works erratically

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=232280

            Bug ID: 232280
           Summary: Missing 'from' selector on @keyframes works
                    erratically
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Mac (Intel)
                OS: macOS 11
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Animations
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: jzabinski at dolios.dev
                CC: dino at apple.com, graouts at apple.com

When @keyframes rules are used to animate elements and the 'from' selector is missing, the animation behaves erratically.
See this example:

https://stackblitz.com/edit/web-platform-vmalvc?file=styles.css

styles.css contains this @keyframes rule:

@keyframes dash {
  to {
    stroke-dashoffset: 0;
  }
}

Running the project in Safari Technology Preview, I find that the line is animated erratically: anywhere from 20-60% of the time. If I add the 'from' keyword:

@keyframes dash {
  from {
    stroke-dashoffset: 14.7;
  }
  to {
    stroke-dashoffset: 0;
  }
}

The animation seems to happen consistently.

W3C says that 'If a 0% or from keyframe is not specified, then the user agent constructs a 0% keyframe using the computed values of the properties being animated.' That computation does not seem to be happening consistently. (Other browsers like Chrome work fine.)

(Reference: https://www.w3.org/TR/css-animations-1/)

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