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

[Gregg Tavares]

On Thu, Mar 14, 2013 at 12:46 PM, Dean Jackson <dino at apple.com> wrote:

> I'm not sure I like this proposal. Why is canvas special? Why doesn't
> <img> get an opaque attribute (or flag)? Why not every element?
>
> I don't think the performance benefit, which is mostly going to be on very
> limited hardware, is worth changing the rendering model that is consistent
> across every other part of the Web.
>

This is why a context creation parameter .... getContext("...",
{alpha:false})  makes sense.

It's labeling the content as having no alpha. Just like a JPG has no alpha.
You don't specify the optimization, you just specify the content. The UA
can decide if it can optimize on its own.




>
> Dean
>
> On 15/03/2013, at 4:53 AM, Stephen White <senorblanco at chromium.org> wrote:
>
> Hi Dirk,
>
> There have been at least five options considered, with contributions from
> Chromium, Adobe and Mozilla so far.  The moz-opaque idea was first floated
> by Robert O'Callahan from Mozilla, and Ian Hickson offered to spec it if
> another browser vendor wanted to implement it.  I took him up on that
> offer, and have made my humble effort to massage it into a concrete
> proposal in the linked message above.
>
> After proposing it here, the alternative suggestion is to sync it up with
> the WebGL syntax, and use a context creation object at getContext() time
> rather than an attribute on the <canvas> element.  I have no strong
> feelings about this either way, and I'm working on a patch to try out the
> WebGL approach (I already have a WebKit patch which implements the
> platform-independent parts of the opaque attribute approach).  However, if
> we do go that way, I'd prefer not to make this proposal conditional on
> changes to the WebGL spec, concerns which I've outlined over on what-wg.
>
> Stephen
>
>
> On Wed, Mar 13, 2013 at 12:30 PM, 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
>> > _______________________________________________
>> > webkit-dev mailing list
>> > webkit-dev at lists.webkit.org
>> > https://lists.webkit.org/mailman/listinfo/webkit-dev
>>
>>
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