Difference in arc rendering between cairo and skia

[Alexandre Bique]

Hi,

I've got two arc renderings, I'm not sure how to share them?

The first one is made with cairo and the second one with skia.

The cairo one's anti-aliasing seems to fades-out to black while the skia one fades out to transparancy.

Is there a setting to control this behavior in skia?
I think that cairo's approach feels sharper and stands out more, what's your thought?

Cheers,

Alex

[Jim Van Verth]

Can you attach the images to an email? It's hard to judge without something to look at.

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Jim Van Verth | Software Engineer | Google.com

[Alexandre Bique]

I could not attach the picture to the post, google group rejected id.

I've uploaded it here: https://we.tl/t-cyUrRfHDwP

After a discussion with my colleagues we think that skia is doing the right thing.

[John Stiles]

It looks like Skia is rendering as expected.

I'm not entirely sure why your Cairo image fades to a darker color when it's being antialiased, but that isn't how an antialiased edge should be rendered. Is it possible that you are drawing a "premultiplied-alpha" image as if it were "unpremultiplied-alpha"? That might explain the discrepancy. If these terms are unfamiliar to you, see https://nigeltao.github.io/blog/2022/premultiplied-alpha.html (which has some Cairo-specific info a few paragraphs in).

To view this discussion on the web visit https://groups.google.com/d/msgid/skia-discuss/73d91de8-bb1c-42a0-ae9d-568c6c7b905fn%40googlegroups.com.