[webkit-dev] New web-facing canvas feature: "opaque" attribute

Gregg Tavares gman at google.com
Wed Mar 13 09:57:35 PDT 2013

It would be nice if this was the same as WebGL instead of different.
Especially because 2d canvas and WebGL need to inter-operate in the near

In WebGL to create a canvas with no alpha (an opaque canvas) you do this

   gl = canvas.getContext("experimental-webgl", { alpha: false });

Why can't 2D canvas be this

   ctx = canvas.getContext("2d", {alpha: false});

As for why this is important to be the same see the proposal for Canvas in
Workers here (http://wiki.whatwg.org/wiki/CanvasInWorkers)

In that proposal the "backingstore" of a canvas can be moved to/from a
worker. That solution may or many not be the final solution but it points
out that whatever solution is chosen we need the solution to work for both
canvas 2d and WebGL and as such needs a common way to create backing stores
with no alpha.

On Wed, Mar 13, 2013 at 9:30 AM, Dirk Schulze <dschulze at adobe.com> wrote:

> This is a very long thread and I did not see any conclusions or agreement
> on this thread. Can you summarize the topic and the status on the
> acceptance level please?
> Greetings,
> Dirk
> On Mar 13, 2013, at 9:15 AM, Stephen White <senorblanco at chromium.org>
> wrote:
> > Hi WebKittens,
> >
> > I'm planning to implement the canvas "opaque" attribute, as proposed
> here:
> http://lists.w3.org/Archives/Public/public-whatwg-archive/2013Mar/0109.html
> .
> >
> > This is an attribute that causes the allocation of an opaque backing
> store for <canvas>, allowing optimizations at the time the canvas is
> composited into the page, such as disabling blending and culling obscured
> content.  It is based on the moz-opaque attribute currently shipping in
> Firefox.
> >
> > I'll be placing the feature behind the build-time flag
> >
> > Let me know if you have any comments or concerns.
> >
> > Stephen
> > _______________________________________________
> > webkit-dev mailing list
> > webkit-dev at lists.webkit.org
> > https://lists.webkit.org/mailman/listinfo/webkit-dev
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