Cairo Antialiasing Outline Issue?

[Uli Schlachter]

Hi,

Am 20.04.24 um 18:38 schrieb Richard Rosenman:
> Can you see the faint greenish outline within the yellow:

actually, I cannot.

However, I looked at the individual color channels of the image and 
noticed that the blue channel is completely empty except for some 
outline around the lines. This outline "reaches into" the upper part of 
the image. I guess this is what you are talking about.

I don't really know what causes this. As others in the thread wrote, 
this might be some inaccuracies somewhere in the code. However, to me it 
seems more like the lines were drawn against a transparent background 
with antialiasing. The result would look good against a transparent 
background, but not when later drawn against a background of the same color.

But this is just a guess.

If my guess is correct, perhaps you can somehow re-arranges things to 
draw these lines directly against their later background.

Another alternative would be to use "poor man's antialiasing": Draw in a 
higher resolution without antialiasing and scale down later.

If you happen to have a self-contained C program that reproduces this 
problem, I might be able to dig deeper. However, I am not sure how 
helpful the result be to you in the near future.

Cheers,
Uli
-- 
If you have a problem, and you use threads to solve it, then you have 
two problems and four of them happen randomly in a way you cannot 
reproduce but your users suffer.
     -- pq in #wayland