[Webkit-unassigned] [Bug 235757] When interpolating between transform lists partial prefix matches should not use matrix interpolation

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=235757

--- Comment #5 from Martin Robinson <mrobinson at webkit.org> ---
(In reply to Simon Fraser (smfr) from comment #4)
> (In reply to Martin Robinson from comment #0)
> > When interpolating between two transform lists that have a match prefix, for
> > instance:
> > 
> > from transform: translateX(25px) rotate(25deg)
> > to tranform: translateX(100px)
> > 
> > The match prefix should blend together directly and the rest of the list
> > should be blended using matrix interpolation. This especially comes into
> > play when doing multiple rotations around an axis.
>  
> I see this in the CSS Transforms 1 spec[1], but not the level 2 spec [2].
> When does "blend the rest as a matrix" happen, and when does "blend with the
> equivalent identify function" happen?

It's true that the specification doesn't say this explicitly, but it's implied in the next section which discusses accumulation of transform lists:

"Accumulation of two transform lists Va and Vb follows the same steps as interpolation with regards to matching transform functions including padding lists with identity transform functions, converting none to an identity transform function, and converting both arguments to matrices as necessary (see CSS Transforms 1 § 11 Interpolation of Transforms)."

Perhaps this is a specification bug?

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