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

[Brandon Jones]

I think "opaque" vs. "alpha: false" is a matter of opinion. The
functionality doesn't change, regardless of what you call it.

I agree with Gregg that this really should be implemented to reflect the
functionality that WebGL already has. Wether 2D or 3D, there's a lot of
common ground between the various canvas contexts and it doesn't make much
sense to reinvent the wheel when one context type has already implemented
the functionality.

--Brandon


On Wed, Mar 13, 2013 at 1:02 PM, Maciej Stachowiak <mjs at apple.com> wrote:

>
> An attribute on the canvas element would presumably be equally applicable
> to all contexts. Is there a reason that it's better to have opaqueness
> specified at context creation time instead of on the canvas? Also, I think
> "opaque" is easier to understand than "alpha: false".
>
>  - Maciej
>
> On Mar 13, 2013, at 9:57 AM, Gregg Tavares <gman at google.com> wrote:
>
> 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
> future.
>
> 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
>> ENABLE(OPAQUE_CANVAS).
>> >
>> > Let me know if you have any comments or concerns.
>> >
>> > Stephen
>> > _______________________________________________
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>>
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