[cairo] [Cairo] Question about anti-alias

Taekyun Kim podain77 at gmail.com
Sun Mar 20 22:18:05 PDT 2011


I have some questions about exact semantics of anti-alias.

General anti-alias steps:
1. calculate coverage of a pixel
2. apply coverage to source pixel
3. composite with destination

So my question is

In step 2, how are the coverages applied to source pixels?
If the source pixel has no alpha (something like rgb_24), does cairo
treat it same with rgba_32 with 1.0 alpha?
Coverage will be multiplied to source alpha channel as well as source rgb
color channels to keep them in premultiplied form, right?

In step 3, if the operator is SRC and the destination format is rgb_24, what
about source pixels with coverage less than 1.0?
They are blended or not?
I think this is the same problem with compositing rgba_32(premultiplied) to
rgb_24 with operator SRC.
Are they converted into unpremultiplied form or just copyed rgb to rgb?

I think just turning on anti-alias should not cause huge visual difference.
(that's just a hint as written in cairo API reference manual)

Thanks in advance.

Best Regards,
Taekyun Kim
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.cairographics.org/archives/cairo/attachments/20110321/9c693449/attachment.html>

More information about the cairo mailing list