[Bug]: Style flag errors trying to save figures as PDF with font Inter #29396

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1. anntzer

   added

   status: confirmed bug

   topic: text/fonts

   on Jan 4, 2025
2. anntzer commented on Jan 4, 2025

   

   anntzer

   on Jan 4, 2025

   Last edited by anntzer

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   Note for repro: to trigger the bug it may be necessary to use the explicit path to the "bad" (actually, variable) font, i.e. something like

   from pylab import *; from pathlib import Path
   figtext(.5, .5, "foo", font=Path("/path/to/InterVariable.ttf"))  # or font="Inter Variable" also seems to "work" here
   savefig("/tmp/test.pdf")

   but the bug is valid.

   It basically arises because of the conversion of FT_STYLE_FLAG_XXX to enum.Flag (regression in #28842), which means that any unknown value in style_flags raises the error seen above. Note that such values are explicitly allowed by the FreeType docs (https://freetype.org/freetype2/docs/reference/ft2-face_creation.html#ft_facerec): "[Since 2.6.1] Bits 16-30 hold the number of named instances available for the current face if we have a GX or OpenType variation (sub)font. Bit 31 is always zero (that is, style_flags is always a positive value). Note that a variation font has always at least one named instance, namely the default instance."

   There's a few fixes possible there:

   • switch the use of enum.Flag to enum.IntFlag, which allows "unregistered" high bits; probably the easiest fix by far.
   • or, on Py3.11+ only, use boundary=KEEP when declaring the enum (the easiest way to do so with the current pybind11 enum machinery is probably p11x::enums["StyleFlags"].attr("_boundary_") = py::module::import("enum").attr("KEEP"); at the same place as where the enum docs are set, but one can probably also adjust the P11X_DECLARE_ENUM macro to avoid touching at semi-internal APIs if desired). However I don't think there's an equivalent available on Py3.10.
   • or, split out bits 16-30 of style_flags (per the documentation) and store them in a separate attribute, as they are semantically separate.

   Note that face_flags likely suffers from the same issue; at least, the commented out FaceFlag values in ft2font_wrapper.cpp's P11X_DECLARE_ENUM("FaceFlags", ...) should probably be ifdef'd as done in DECLARE_FLAG just above.
3. anntzer

   added

   Release criticalFor bugs that make the library unusable (segfaults, incorrect plots, etc) and major regressions.For bugs that make the library unusable (segfaults, incorrect plots, etc) and major regressions.

   on Jan 4, 2025
4. anntzer

   added this to the v3.10.1 milestone on Jan 4, 2025
5. QuLogic commented on Jan 8, 2025

   

   QuLogic

   on Jan 8, 2025

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   Note that face_flags likely suffers from the same issue; at least, the commented out FaceFlag values in ft2font_wrapper.cpp's P11X_DECLARE_ENUM("FaceFlags", ...) should probably be ifdef'd as done in DECLARE_FLAG just above.

   These can't be #ifdef because P11X_DECLARE_ENUM is a macro invocation. If we could rewrite that as some kind of template, then it might be possible, but not as a macro.
6. anntzer commented on Jan 8, 2025

   

   anntzer

   on Jan 8, 2025

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   Good catch. The following appears to work, though:

   #ifdef FT_FACE_FLAG_VARIATION
       #define FACE_FLAG_VARIATION {"VARIATION", FaceFlags::VARIATION},
   #else
       #define FACE_FLAG_VARIATION
   #endif
   P11X_DECLARE_ENUM(
       "FaceFlags", "Flag",
       {"SCALABLE", FaceFlags::SCALABLE},
       {"FIXED_SIZES", FaceFlags::FIXED_SIZES},
       {"FIXED_WIDTH", FaceFlags::FIXED_WIDTH},
       {"SFNT", FaceFlags::SFNT},
       {"HORIZONTAL", FaceFlags::HORIZONTAL},
       {"VERTICAL", FaceFlags::VERTICAL},
       {"KERNING", FaceFlags::KERNING},
       {"FAST_GLYPHS", FaceFlags::FAST_GLYPHS},
       {"MULTIPLE_MASTERS", FaceFlags::MULTIPLE_MASTERS},
       {"GLYPH_NAMES", FaceFlags::GLYPH_NAMES},
       {"EXTERNAL_STREAM", FaceFlags::EXTERNAL_STREAM},
       {"HINTER", FaceFlags::HINTER},
       {"CID_KEYED", FaceFlags::CID_KEYED},
       {"TRICKY", FaceFlags::TRICKY},
       {"COLOR", FaceFlags::COLOR},
       FACE_FLAG_VARIATION  // backcompat: ft 2.9.0.
       // ditto for the others
   );
7. oscargus

   closed this as completedin #29431on Jan 8, 2025