[whatwg] Adding blending to the canvas API

[Rik Cabanier]

All,

I'm working on a spec to add blending and compositing through simple CSS
keywords. It is trying to define a generic model that is not specific to
Canvas, HTML or SVG and then lists how the model could be implemented.
We've gotten some comments that this feature would be useful in Canvas as
well so I was wondering if it made sense to add it to the canvas API.

I can see 2 ways of adding this:
1. extend the list of compositing operators (
http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#compositing)
with blending. This is what is currently in the draft spec (
https://dvcs.w3.org/hg/FXTF/rawfile/tip/compositing/index.html chapter 7)

2. create a new attribute on the context called 'globalBlendOperation' that
takes the same list of blend operations as css (
https://dvcs.w3.org/hg/FXTF/rawfile/tip/compositing/index.html#blend-mode)

Any thoughts?