[whatwg] Canvas - globalCompositeOperation

[Vladimir Vukicevic]

Philip Taylor wrote:
 > [...]

Cool stuff!  I'll look through your tests and fix up the mozilla 
implementation as much as possible.

> I would be happy if "darker" was removed from the spec - there isn't
> an obvious definition for it, and it's not interoperably implemented
> at all and it sounds like it never will be. Existing implementations
> can add "apple-plusdarker", "moz-saturate", etc, if they still want to
> provide the old functionality.

I'd be happy with getting rid of it.

> "lighter" seems much easier to define, and more useful, so I think
> it's perhaps worth keeping - but it looks like a pain for those using
> Qt/Java/etc libraries which don't support anything other than the
> standard Porter-Duff operators, and I don't know if it's a difficulty
> for Opera to fix their implementation of it. Does anyone have views on
> this or on "darker"?

Well, if we have lighter, we should keep darker; I think that for 
mozilla at least, we can implement this using some slow-boat fallback 
mechanism -- basically, render the path/image to a separate surface, 
then manually do the requested math if things don't map directly to one 
of our operators; this is what our SVG impl does now for many of the SVG 
filters.

     - Vlad