Re: [css3-transitions] interpolation between value types

On Tue, Nov 8, 2011 at 2:37 PM, Jennifer Yu <Jennifer.Yu@microsoft.com> wrote:
> While http://dev.w3.org/csswg/css3-transitions/#animation-of-property-types-
> describes how each property type undergoes a transition, it doesn’t define
> how interpolation should occur between value types. eg. between a percentage
> and a length.
>
> I would imagine that you’d compute a length from the percentage, then
> interpolate over the lengths. But this is a little more complicated in the
> case of background-position, for instance. If you have:
>
> {
> background-image: url('1.gif'), url('2.gif'), url('3.gif');
>                 background-size: 100px 100px, 200px 200px, 300px 300px;
>                 background-position: 50%;
>                 transition: background-position 5s;
>                 width: 500px;
>                 height: 500px;
> }
>
> then set element.style.backgroundPosition=”100px”;
>
> What does a transition and its corresponding computed value look like in
> this case?

I believe the intention is to use calc() to represent the intermediate state.

background-position is underdefined in this aspect.

~TJ