W3C home > Mailing lists > Public > www-style@w3.org > July 2012

[css3-transforms] interpolation of transform lists

From: L. David Baron <dbaron@dbaron.org>
Date: Thu, 19 Jul 2012 17:38:26 -0400
To: www-style@w3.org
Message-ID: <20120719213826.GA8775@crum.dbaron.org>
http://dev.w3.org/csswg/css3-transforms/Overview.html#animation
says something that's not compatible with earlier drafts of the
transforms spec.  In particular, I'm concerned about the "is a
derivative of a primitive" in:
  # If from- and to-transform have the same number of transform
  # functions, each transform function is a derivative of a
  # primitive and each function pair is a derivative of the same
  # primitive. 
and the later text:
  # Transform functions not listed above are neither primitives nor
  # derivatives and can neither be interpolated with transform
  # functions of primitives listed above nor with itself. UAs have
  # to follow the last rule on Interpolation of Transforms then.

Earlier drafts said that any matched list of transform functions is
interpolated function-by-function rather than via matrix
interpolation.  The new draft adds this concept of primitives to say
that some pairs of syntactically-different but semantically-similar
functions (e.g., translate() and translateX()) can be considered
equivalent for the purpose of this matching.  I think this is fine.

But it also says that some transform functions:  in particular,
perspective(), rotate3d(), matrix(), and matrix3d().  I could
understand the desire to interpolate these (or maybe all of these
except perspective()) as matrices, but it seems inappropriate for
the presence of one of these in a transform list to force other
items in that transform list into the matrix decomposition path,
particularly if it's the other items that are changing in the
animation.

We're planning not to implement this as described in Gecko, but
instead to consider all transform functions to be primitives (which
is more compatible with the behavior prior to the introduction of
the concept of primitives).

-David

-- 
𝄞   L. David Baron                         http://dbaron.org/   𝄂
𝄢   Mozilla                           http://www.mozilla.org/   𝄂
Received on Thursday, 19 July 2012 21:38:50 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 17:20:57 GMT