Cairo: Switch back to character codes for mathtext#32101
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Since f630b48, the Cairo backend was switched to use glyph indices for mathtext, just as the Agg backend. Unfortunately, neither Pycairo nor cairocffi expose anything other than the toy font face API. This means the Cairo backend can only access fonts by family name and not explicit path. Apparently, the version of DejaVu Sans that we ship may differ from the system copy WRT glyph indices, so we need to switch back to character codes, which are standardized and won't cause the wrong glyph to be rendered accidentally. Fixes matplotlib#32084
scottshambaugh
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Jul 23, 2026
scottshambaugh
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My bundled / system dejavusans math glyphs indices are off by one, and I tested this locally as resolving it.
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PR summary
Since f630b48, the Cairo backend was switched to use glyph indices for mathtext, just as the Agg backend.
Unfortunately, neither Pycairo nor cairocffi expose anything other than the toy font face API. This means the Cairo backend can only access fonts by family name and not explicit path. Apparently, the version of DejaVu Sans that we ship may differ from the system copy WRT glyph indices, so we need to switch back to character codes, which are standardized and won't cause the wrong glyph to be rendered accidentally.
I can't really add a test, as in order to break, this requires a system-installed copy of DejaVu Sans of the right version that it has different glyph indices.
Fixes #32084
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