[TextServer] Reset subpixel shift on blank glyphs.

[bruvzg]

Fixes #98659

Regression from #93256, accumulated subpixel shift remainder was unnecessarily preserved over word/line break.

[Lielay9]

Mandatory linebreaks work, BREAK_ADAPTIVE and BREAK_GRAPHEME_BOUND still cause issues (first line missmatch expected but second and third should be identical),

[Lielay9]

Additionally, even content on the same line is rather flickery compared to 4.2.

FLICKERING WARNING!

4.4 ,

BADDY_CROPPED.mp4

4.2 ,

GOODY_CROPPED.mp4

[bruvzg]

Additionally, even content on the same line is rather flickery compared to 4.2.

That's looks expected, kerning always have subpixel values, and glyphs are aligned to the pixel boundaries. If you do not want it to be aligned, enable subpixel positioning in the font import settings.

Mandatory linebreaks work, BREAK_ADAPTIVE and BREAK_GRAPHEME_BOUND still cause issues (first line missmatch expected but second and third should be identical),

Enabling subpixel positioning should fix it as well. Fixing it for the pixel aligned font require either full resahping of the sub-strings (a big performance impact), or moving rounding step to draw (can't be done since draw calls do not have any global context), or rounding each glyph position individual (like it was in 4.2, which will reintroduce #93199). I guess we can make #93256 and optional import setting as well.

[Lielay9]

That's looks expected, kerning always have subpixel values, and glyphs are aligned to the pixel boundaries. If you do not want it to be aligned, enable subpixel positioning in the font import settings.

Thanks, using more aggressive subpixel setting seems to alleviate most of the remaining issues.

Enabling subpixel positioning should fix it as well. Fixing it for the pixel aligned font require either full resahping of the sub-strings (a big performance impact), or moving rounding step to draw (can't be done since draw calls do not have any global context), or rounding each glyph position individual (like it was in 4.2, which will reintroduce #93199). I guess we can make #93256 and optional import setting as well.

I cannot speak for the technical side so I have no opinion on that front. That said, the issue (#98659) was found in our accessibility tests flagging a multiline text editor as a potential source of epilepsy. Of course, sizable blocks of text are notoriously bad for photosensitive individuals moving or not, but flickering is definitely not helping (read more). It might be a false flag on our part, but I'd rather err on the side of caution in these kind of issues.

Therefore, if I'm to understand that #93256 is necessary for some fonts to function correctly and fixing the remaining issues isn't feasible, I'm in favor of exposing the original behavior. In addition, maybe the AUTO subpixel positioning could be made more aggressive? It seems to only take effect on sizes no game should probably even use.

[akien-mga]

Thanks!