Re: CAIRO_OPERATOR_XOR documentation
Bryce Harrington <[email protected]>
| Newsgroups | gmane.comp.lib.cairo |
|---|---|
| Message-ID | <[email protected]> |
On Mon, Apr 06, 2015 at 06:36:53PM -0700, Richard Billington wrote:
> If I interpret this correctly (quoting from
> http://cairographics.org/operators/):
>
> Resulting alpha (aR) Resulting color (xR)
> aA + aB − 2·aA·aB (xaA·(1−aB) + xaB·(1−aA))/aR
>
> If the alpha value for both A and B is 1, then nothing will be drawn
> anywhere? That is, I have something drawn on surface A with alpha at
> 1.0, and I have something on the receiving surface drawn with alpha
> at 1.0. This results in aR = 0.0 so everything in B becomes
> transparent?
Check the truth table for XOR:
https://en.wikipedia.org/wiki/Exclusive_or
Also, look down at the xor example on the alpha blending page
https://en.wikipedia.org/wiki/Alpha_compositing
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