[Webkit-unassigned] [Bug 216107] New: Negative values in cubic-bezier transform transitions do not work

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=216107

            Bug ID: 216107
           Summary: Negative values in cubic-bezier transform transitions
                    do not work
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Animations
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: joseph at inventivelabs.com.au
                CC: dino at apple.com

Created attachment 407829

  --> https://bugs.webkit.org/attachment.cgi?id=407829&action=review

Save as HTML and open in latest Webkit! "Animate: transform" is broken behavior; "Animate: top" is expected behavior.

When a CSS cubic-bezier easing function contains a negative value, and the transition property is `transform`, the property doesn't animate while in the negative range. It starts animating when the easing function enters the positive range.

**See attachment** for bug reduction with `transform` and expected behavior with `top`. The expected behavior with `transform` is observed in iOS 13, Chrome, and Firefox.

This bug was introduced between Safari 13 and 14. We have been using this animation feature at https://libbyapp.com for several years, and noticed it broke in Saf 14 betas.

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