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

[Elliott Sprehn]

alpha:false is super confusing to me. It makes it sound as though all
draw*() operations that use an alpha channel will fail... does globalAlpha
still work?

It's sad that WebGL picked such a generic name that isn't about all "alpha"
related things.


On Wed, Mar 13, 2013 at 2:59 PM, Rik Cabanier <cabanier at gmail.com> wrote:

> The main reason for this feature is to enhance performance of canvas
> operations.
> Are we certain that this will always be the case? For instance, is google
> going to make certain that the cairo and core graphics backends don't slow
> down?
>
> Rik
>
>
> On Wed, Mar 13, 2013 at 1:21 PM, Brandon Jones <bajones at google.com> wrote:
>
>> 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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>>
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