PR summary

This is internal API for querying font variations and setting them. FreeType sometimes calls them MM (multiple master) vars or variation axes, but I tried to stick to variations/variation axis. For the named styles, FreeType sometimes calls that a named style or a named instance, and I tried to use named style everywhere.

Font variations essentially allow fonts to have multiple styles in one by varying some parameter along an "Axis". For example, one font can contain all weights with a Weight axis ranging from Thin to Extra Bold, or an upright and italic font with a Slant axis for the angle. Some fonts may contain named styles which group some specific settings together under a a name (e.g., Bold may be Weight=700 or whatever the designer decides.)

Current internal API additions are:

• FT2Font.get_variation_descriptor which returns a list of the variation axes and a list of the named styles.
• FT2Font.get_default_variation_style which returns the index of the default name style (in the above list.)
• FT2Font.get_variations which returns the float values for each axis (in the order of the above list.)
• FT2Font.set_variations which allows setting the float values for each axis as a list, or selecting a named style by index.

This does not contain any public API; for that there are some questions that we might need to think about:

• Should users select a font (by name or otherwise) and then apply variations with something like Text.set_fontvariations and/or FontProperties.set_variations?
• Or, should variable fonts match anything within their range?
  • That is, if a variable font has a Weight axis between 100 and 1000, should that font automatically match ("FontName", weight="bold") / ("FontName", weight="regular"), etc.
  • If a variable font has a named style for, e.g., Bold, should that automatically add a name of "FontName Bold" as well (as in ENH: Allow fonts to be addressed by any of their SFNT family names #31183)?

I do not expect this to be ready for 3.11 until we discuss some of these options.

AI Disclosure

None

PR checklist

• "closes #0000" is in the body of the PR description to link the related issue
• new and changed code is tested
• Plotting related features are demonstrated in an example
• New Features and API Changes are noted with a directive and release note
• Documentation complies with general and docstring guidelines