[whatwg] Fwd: RE: Inconsistent behaviour of globalCompositeOperation property - Drawing model discussion

[Robert O'Callahan]

On Wed, Jan 5, 2011 at 12:05 PM, <carol.szabo at nokia.com> wrote:

>
> Given the statements above I no longer think that changing the spec in this
> regard is a good thing, but I still believe that the disappearance of
> shadows for the source-in and copy modes and the strange result when shadows
> are drawn and the composite operation is source-out should be corrected. To
> do this I suggested the following in my previous e-mail, but I got no
> comments about my suggestion so I repeat it here (please excuse my
> insistence):
>
> Replace steps 3 to 6 of the drawing model, with:
>
> 3. When shadows are drawn<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#when-shadows-are-drawn>,
> composite B (source) with A (destination) using destination-over operation.
>
>
> 4. Multiply the alpha component of every pixel in A by globalAlpha<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-context-2d-globalalpha>
> .
>
> 5. Composite A within the clipping region<http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#clipping-region>over the current canvas bitmap using the current composition operator.
>

That might work. However, I have an alternative proposal: if we don't have
good use cases for using shadows with non-"source-over" operators (I don't),
let's just say that shadows don't draw for non-"source-over" operators. That
would reduce spec and implementation complexity.

Rob
-- 
"Now the Bereans were of more noble character than the Thessalonians, for
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