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Remove fallback code for glyph indices#30168

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Merged

QuLogic merged 1 commit intomatplotlib:text-overhaulfromQuLogic:no-glyph-fallback

Jun 19, 2025

Merged

Remove fallback code for glyph indices#30168

QuLogic merged 1 commit intomatplotlib:text-overhaulfromQuLogic:no-glyph-fallback

Jun 19, 2025

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QuLogic commentedJun 12, 2025

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 callingFT2Font.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 fromthetext-overhaul-images branch, 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-overhaul branch.

PR checklist

[n/a] "closes #0000" is in the body of the PR description tolink the related issue
new and changed code istested
[n/a]Plotting related features are demonstrated in anexample
[n/a]New Features andAPI Changes are noted with adirective and release note
[n/a] Documentation complies withgeneral anddocstring guidelines

Remove fallback code for glyph indices

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Glyph indices are specific to each font. It does not make sense to fallback based on glyph index to another font.This could only really be populated by calling `FT2Font.set_text`, buteven that was fragile. If a fallback font was used for a character withthe same glyph index as a previous character in the main font, thenthese lookups could be overwritten to the fallback instead of the mainfont, with a completely different character!Fortunately, nothing actually uses or requires a fallback through glyphindices.

QuLogic added this to thev3.11.0 milestone

Jun 12, 2025

QuLogic added this toFont and text overhaul

Jun 12, 2025

QuLogic added the Maintenance label

Jun 12, 2025

github-project-automationbot moved this toWaiting for other PR inFont and text overhaul

Jun 12, 2025

github-actionsbot added topic: mplot3d topic: text/fonts labels

Jun 12, 2025

QuLogic moved this fromWaiting for other PR toReady for Review inFont and text overhaul

Jun 12, 2025

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QuLogic commentedJun 13, 2025•
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As an example, in DejaVu Sans, the letter A is glyph index 36:

>>> dejavu = FT2Font('lib/matplotlib/mpl-data/fonts/ttf/DejaVuSans.ttf')>>> dejavu.get_char_index(ord('A'))36

which has metrics like:

>>> g = dejavu.load_glyph(36)>>> g.bbox(6, 0, 519, 576)

In the Last Resort font, the Tibetan block is glyph index 36:

>>> lastresort = FT2Font('lib/matplotlib/mpl-data/fonts/ttf/LastResortHE-Regular.ttf')>>> lastresort.set_charmap(0)>>> lastresort.get_char_index(ord('\U00000F00'))36>>> g = lastresort.load_glyph(36)>>> g.bbox(72, -167, 808, 578)

So if we have a string with both using fallbacks, then the last glyph 'wins':

>>> font = FT2Font('lib/matplotlib/mpl-data/fonts/ttf/DejaVuSans.ttf', _fallback_list=[lastresort])>>> font.set_text('A\U00000F00')array([[  0.,   0.],       [528.,   0.]])>>> g = font.load_glyph(36)>>> g.bbox(72, -167, 808, 578)

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!