[whatwg] Canvas Proposal: aliasClipping property
oliver at apple.com
Fri Oct 16 21:37:11 PDT 2009
On Oct 16, 2009, at 8:10 PM, Robert O'Callahan wrote:
> On Sat, Oct 17, 2009 at 4:01 AM, Philip Taylor <excors+whatwg at gmail.com
> > wrote:
> Yes, mostly. http://philip.html5.org/tests/canvas/suite/tests/index.2d.composite.uncovered.html
> has relevant tests, matching what I believed the spec said - on
> Windows, Opera 10 passes them all, Firefox 3.5 passes all except
> 'copy' (https://bugzilla.mozilla.org/show_bug.cgi?id=366283), Safari 4
> and Chrome 3 fail them all.
> (Looking at the spec quickly now, I don't see anything that actually
> states this explicitly - the only reference to infinite transparent
> black bitmaps is when drawing shadows. But
> is phrased in terms of rendering shapes onto an image, then
> compositing the image within the clipping region, so I believe it is
> meant to work as I said (and definitely not by compositing only within
> the extent of the shape drawn onto the image).)
> Yes, I think that's pretty clear as written.
> I think there is a reasonable argument that the spec should be
> changed so that compositing happens only within the shape. (In cairo
> terminology, all operators should be bounded.) Perhaps that's what
> Safari and Chrome developers want.
This is the behaviour of the original canvas implementation (and it
makes a degree of sense -- it is possible to fake composition implying
an infinite 0-alpha surrounding when the default composite operator
does not do this, but vice versa is not possible). That said I
suspect we are unable to do anything this anymore :-/
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