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Re: [css-compositing] Request to move Compositing and Blending spec to CR

From: Robert O'Callahan <robert@ocallahan.org>
Date: Fri, 13 Dec 2013 18:24:14 +1300
Message-ID: <CAOp6jLaC9tfMuSFVy8iOfbkHSRY8UrHYpduo4AmQCzs+Moj7rQ@mail.gmail.com>
To: Rik Cabanier <cabanier@gmail.com>
Cc: James Robinson <jamesr@google.com>, www-svg <www-svg@w3.org>, www-style list <www-style@w3.org>, "public-fx@w3.org" <public-fx@w3.org>
On Fri, Dec 13, 2013 at 4:50 PM, Rik Cabanier <cabanier@gmail.com> wrote:

> On Thu, Dec 12, 2013 at 7:29 PM, Robert O'Callahan <robert@ocallahan.org>wrote:
>
>> On Fri, Dec 13, 2013 at 4:13 PM, Rik Cabanier <cabanier@gmail.com> wrote:
>>
>>> No, the spec should not refer to blogs. Also, this is not 'potentially'
>>> useful as the absence of this description has caused confusion in the past.
>>>
>>
>> I agree with James. Having the spec define behavior that is never used by
>> any Web feature is very confusing.
>>
>> Section 4 is not really needed at all since the HTML5 canvas spec defines
>> the canvas compositing behavior.
>>
>
> Can you point where that is defined in the canvas spec?
>

http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#drawing-model


>
>
>> If you want the Compositing and Blending spec to define new compositing
>> modes for canvas, then define a list of operators that the HTML canvas spec
>> can refer to, but don't define globalCompositeOperation here. Don't even
>> mention canvas here.
>>
>
> It's needed because the canvas spec doesn't say anything about how
> compositing should happen.
> I don't want to break canvas by removing this.
>

All you need to define for canvas is the per-pixel compositing behavior.


>
> Another very important reason is also that if this property/behavior is
>>> included in the spec, the W3C patent policy will apply.
>>>
>>
>> Describing something in a W3C spec that is not actually used by any
>> features in that spec, just so we can get the patent policy to apply to it,
>> borders on bad faith.
>>
>
> It *is* being used.
>

Where? Pointing to "clip to self" saying "don't do this" does not
constitute a use.


> Also, future spec might want to refer to this. Another example is the
> proposal for masking in canvas which has an option for clip-to-self. It
> would be unfortunate that we would have to rev the compositing spec to
> progress canvas or filters.
>

If a future spec will use it, the future spec can define it. Any use of
clip-to-self will have to define what the clip-to-self region is for each
drawing operation, which is not necessarily easy to do. It certainly
shouldn't be done by saying the clip-to-self region is where alpha > 0, for
the reasons James pointed out near the beginning of this thread.

Rob
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Received on Friday, 13 December 2013 05:24:41 UTC

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