fix: text rendering did not work correctly with alpha #3934
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Signed-off-by: Nicolas VIVIEN <nicolas@vivien.fr>
lgritz
changed the title
lgritz
reviewed
Aug 11, 2023
| if (c == alpha_channel) | ||
| pixelcolor[c] = alpha + (1.0f - alpha) * pixelcolor[c]; | ||
| else | ||
| pixelcolor[c] = (val * alpha * textcolor[c]) + (1.0f - alpha) * pixelcolor[c]; |
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You may have noticed CI failures. Basically, every test with text in it is failing with this PR.
I think this line is the part that's responsible. Compared to the old code, you have an extra multiplication of the foreground color by alpha. I believe (but admit that I am not 100% sure) that it was correct before because freetype is supplying color results that are already scaled by the glyph's alpha coverage, so now you are doubly accounting for alpha coverage in the foreground.
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@progweb Any comments on the last concerned I raised about the CI failure? |
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Not available, I’ll fix this in few days for the next week. |
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As render text with shadow with channel alpha, I don't get the same result that without channel alpha.
Without channel alpha, shadow option permit to draw a dilated text in black, whereas with channel alpha, OIIO makes a gap...
Working with dev-2.2 branch, I can see the same issue on master branch.
In using this patch, shadow option works as expected on image with alpha buffer.
Ref: #3932
[Note]: OpenImageIO is used in the gpx2video project.