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

Why are you trying to define how canvas works in a CSS spec? Canvas is
defined as part of HTML, including how the compositing operations are
applied. The text here is completely unhelpful.

- James
On Dec 11, 2013 7:16 PM, "Rik Cabanier" <cabanier@gmail.com> wrote:

>
>
>
> On Wed, Dec 11, 2013 at 6:57 PM, James Robinson <jamesr@google.com> wrote:
>
>>
>> On Wed, Dec 11, 2013 at 6:44 PM, Rik Cabanier <cabanier@gmail.com> wrote:
>>
>>>
>>>
>>>>
>>>> Canvas is defined in HTML.  Having text here to define a behavior that
>>>> canvas does not use is just confusing with no upside.
>>>>
>>>
>>> No, canvas refers to the compositing spec for the 'globalComposite'
>>> operator [1]:
>>>
>>> The globalCompositeOperation attribute sets the current composition
>>> operator, which controls how shapes and images are drawn onto the scratch
>>> bitmap<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#scratch-bitmap>,
>>> once they have had globalAlpha<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-context-2d-globalalpha> and
>>> the current transformation matrix applied. The possible values are those
>>> defined in the Compositing and Blending specification. [COMPOSITE]<http://www.whatwg.org/specs/web-apps/current-work/multipage/references.html#refsCOMPOSITE>
>>>
>>>
>>> Do you think the canvas spec should be more clear that compositing is
>>> defined in the "Compositing and Blending specification"?
>>>
>>
>> The paragraph in question -  "9.2.3. Clip to self behavior" - describes a
>> behavior that is not used by canvas, or (from what you've said) by anything
>> in the Compositing and Blending spec.  What value does it have other than
>> creating confusion, in that case?
>>
>
> Section 5-10 define a generic model for blending and compositing.
> The normative section defines a subsection of that model. Hopefully we can
> implement the whole model over the coming years.
> By defining it this way, it should be more clear to an implementor how
> things are supposed to be work.
> For example, the problems that you mentioned earlier:
>
> Firefox applied the compositing operation to the entire canvas, respecting
> the current clip, and WebKit applied the compositing operation only to the
> "bounds" of the draw.
>
>  would not have happened if there had been a definition like you find in
> the current spec:
> http://dev.w3.org/fxtf/compositing-1/#groupcompositingcliptoself
>
> I don't really see a way to define how compositing works in canvas without
> describing the clip-to-self behavior somehow...
>