Re: [css-compositing] How do 'alpha-compositing' and 'blend-mode' interact?

On Sat, Jul 21, 2012 at 11:21 AM, Maciej Stachowiak <mjs@apple.com> wrote:

>
> How do 'alpha-compositing' and 'blend-mode' interact if you have set both?
> I was unable to determine this from the spec. Does it actually make sense
> to specify both to non-default values at the same time?


Yes, it does in certain use cases.
Say for instance, you have text that is blending with a video underneath,
but I also want the text to clip the video. (see for instance the Marvel
trailer : http://www.youtube.com/watch?v=aTDNosVEEyk)


> I was unable to understand what their relationship is supposed to be.
>
>
> Some other comments:
>
> - The property values for the 'alpha-compositing' operator are
> inconsistent with the values for HTML5 Canvas: <
> http://www.w3.org/TR/2dcontext/#dom-context-2d-globalcompositeoperation>.
> I suggest making them match if there is no compelling advantage to the new
> names, otherwise this will be needlessly confusing to authors.
>
> - Consider renaming 'alpha-compositing' to 'composite-operator' for
> similar reasons.
>
> Regards,
> Maciej
>
>
>