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[whatwg] Canvas Proposal: aliasClipping property

From: Robert O'Callahan <robert@ocallahan.org>
Date: Fri, 9 Oct 2009 11:10:44 +1300
Message-ID: <11e306600910081510q3a959c72u18420b1f33d44ddc@mail.gmail.com>
On Fri, Oct 9, 2009 at 10:51 AM, Charles Pritchard <chuck at jumis.com> wrote:

> Here is a good example of the conflict between Google and Mozilla over
> clip():
> http://www.imperialviolet.org/2009/09/02/anti-aliased-clipping.html
>
> There is another conflict, with the composition modes between the two, with
> Google
> again taking another principled stand. I'm sorry I don't supporting links
> for that,
> but it effects many of the composite operations (at least four of them).
>
> I'm hoping to have both methods supported, I think they are both valuable.
> I've certainly used both methods in my work the past few years.
>
> This is very much about the clipping pipeline.
>

No, it is entirely about antialiasing. Coverage-based antialiasing causes
problems whenever you draw two objects with adjacent edges that aren't
aligned to pixel boundaries. It doesn't matter whether those boundaries are
induced by clipping or just by filling a path. The post you linked to even
refers to this:

The second problem with anti-aliasing, even when done correctly, is that it
> makes it impossible to put polygons next to each other. Try this demo<http://tulrich.com/geekstuff/canvas/perspective.html>in Firefox and note the hairlines caused by anti-aliasing.
>

Personally I'm not a big fan of coverage-based antialiasing for exactly this
reason, but it's the most common antialiasing technique in graphics
libraries so it's hard to get away from.

Rob
-- 
"He was pierced for our transgressions, he was crushed for our iniquities;
the punishment that brought us peace was upon him, and by his wounds we are
healed. We all, like sheep, have gone astray, each of us has turned to his
own way; and the LORD has laid on him the iniquity of us all." [Isaiah
53:5-6]
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