Remove fallback code for glyph indices #30168
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Glyph indices are specific to each font. It does not make sense to fall back based on glyph index to another font. This could only really be populated by calling `FT2Font.set_text`, but even that was fragile. If a fallback font was used for a character with the same glyph index as a previous character in the main font, then these lookups could be overwritten to the fallback instead of the main font, with a completely different character! Fortunately, nothing actually uses or requires a fallback through glyph indices.
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As an example, in DejaVu Sans, the letter A is glyph index 36: which has metrics like: In the Last Resort font, the Tibetan block is glyph index 36: So if we have a string with both using fallbacks, then the last glyph 'wins': If we had multiple fonts in the fallbacks, and multiple characters in those fonts that used the same glyph index, then lookup would depend on the order of characters in the text! |
anntzer
approved these changes
Jun 15, 2025
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looks good! Can you please drop the last commit and self-merge? The windows failures are a know issue with a new numpy release that is fixed on main. |
tacaswell
approved these changes
Jun 19, 2025
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Not going to wait for CI, because it's just going to fail, and then run again when merged, and fail there too... |
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PR summary
Glyph indices are specific to each font. It does not make sense to fall back based on glyph index to another font.
This could only really be populated by calling
FT2Font.set_text, but even that was fragile. If a fallback font was used for a character with the same glyph index as a previous character in the main font, then these lookups could be overwritten to the fallback instead of the main font, with a completely different character!Fortunately, nothing actually uses or requires a fallback through glyph indices, and this is all internal to the extension.
Note to reviewers: the second commit here is just the last commit from the
text-overhaul-imagesbranch, but is not actually relevant here. Please only review the first commit as the second will be dropped before merging. If you prefer, I can targetmain, but I thought this was relevant to thetext-overhaulbranch.PR checklist