Description

QuLogic

opened on Jun 25, 2024

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Bug summary

The anatomy example uses italic text for its annotations. When running with TkCairo (or any other Cairo-based backend), this text is just upright.

Code for reproduction

MPLBACKEND=TkCairo python galleries/examples/showcase/anatomy.py

Actual outcome

Expected outcome

Additional information

No response

Operating system

Fedora 40

Matplotlib Version

d7d1bba

Matplotlib Backend

TkAgg/TkCairo

Python version

3.12.3

Jupyter version

n/a

Installation

git checkout

Activity

1. anntzer commented on Jun 25, 2024

   

   anntzer

   on Jun 25, 2024

   Contributor

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   From a quick look, the relevant functions for cairo's "toy" font APIs are cairo{ft,quartz,win32}_font_face_create_for_toy, which do appear to have some (extremely limited) support for style/weight. Now we just need to figure out the right arguments to pass to these (if any...).
2. QuLogic commented on Jun 25, 2024

   

   QuLogic

   on Jun 25, 2024

   MemberAuthor

   More actions

   Well, we do attempt to set the slant and the weight, but I guess that is not sufficient? Or maybe the family name is too specific?
   

   matplotlib/lib/matplotlib/backends/backend_cairo.py

   Lines 62 to 79 in e353367

   	def _cairo_font_args_from_font_prop(prop):
   	"""
   	Convert a `.FontProperties` or a `.FontEntry` to arguments that can be
   	passed to `.Context.select_font_face`.
   	"""
   	def attr(field):
   	try:
   	return getattr(prop, f"get_{field}")()
   	except AttributeError:
   	return getattr(prop, field)
   	name = attr("name")
   	slant = getattr(cairo, f"FONT_SLANT_{attr('style').upper()}")
   	weight = attr("weight")
   	weight = (cairo.FONT_WEIGHT_NORMAL
   	if font_manager.weight_dict.get(weight, weight) < 550
   	else cairo.FONT_WEIGHT_BOLD)
   	return name, slant, weight
3. anntzer commented on Jun 25, 2024

   

   anntzer

   on Jun 25, 2024

   Contributor

   More actions

   I think the family name is too specific (from what I remember looking at the cairo code; haven't re-checked).
   OTOH as the cairo docs say themselves, trying to render text without actually going through freetype (or win32 or quartz) is only implemented as a "toy" in cairo.
   Although pycairo says it can be integrated with freetype-py (https://pycairo.readthedocs.io/en/latest/tutorial/other.html#freetype-py-cairo), from a quick skim at the examples they seem to just extract the bitmap using freetype and blit it (essentially like we do in FT2Font and FT2Image) rather than rendering as glyphs (text on vector output), so that doesn't really help.
   Also cairo's actual freetype integration seems not implented in pycairo (https://pycairo.readthedocs.io/en/latest/reference/text.html#class-freetypefontface-fontface).
   I suspect (though I would be happy to be proven wrong) that fixing this is quickly going to reach mplcairo territory ;-)
4. anntzer

   added

   backend: cairo

   on Apr 22, 2025
5. QuLogic

   added a parent issue on Sep 1, 2026

   • [MNT]: Deprecate internal Cairo backends #32276

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