Font queries ignore `Font.weight`

[corranwebster]

The FontManager and FontQuery system ignore the Font.weight attribute and look for a style which holds flags for BOLD, ITALIC, BOLD_ITALIC, etc. See:

enable/kiva/fonttools/font.py

Lines 149 to 169 in 62f390f

	def _make_font_query(self):
	""" Returns a FontQuery object that encapsulates our font properties.
	"""
	# XXX: change the weight to a numerical value
	if self.style == BOLD or self.style == BOLD_ITALIC:
	weight = "bold"
	else:
	weight = "normal"
	if self.style == ITALIC or self.style == BOLD_ITALIC:
	style = "italic"
	else:
	style = "normal"
	query = FontQuery(
	family=self.familymap[self.family],
	style=style,
	weight=weight,
	size=self.size,
	)
	if self.face_name != "":
	query.set_name(self.face_name)
	return query

But the str_to_font function populates weight. See:

enable/kiva/fonttools/font.py

Lines 54 to 55 in 62f390f

	elif lword in font_weights:
	weight = font_weights[lword]

As does the trait validator:

enable/kiva/trait_defs/kiva_font_trait.py

Lines 122 to 123 in 62f390f

	elif lword in font_weights:
	weight = font_weights[lword]

As does the Wx editor:

enable/kiva/trait_defs/ui/wx/kiva_font_editor.py

Lines 98 to 100 in 62f390f

	weight=(
	kc.NORMAL, kc.BOLD
	)[font.GetWeight() == wx.FONTWEIGHT_BOLD],

To reproduce, you can use kvia_explorer.py with this script and the agg backend:

# The graphics context is available as gc.

from kiva.api import (
    Font, BOLD_ITALIC, BOLD, ITALIC
)
from kiva.fonttools import str_to_font 

font_1 = Font(
    'Courier New',
    style=BOLD_ITALIC,
    size=24,
)
font_2 = str_to_font('24 pt italic bold Courier New')


with gc:
    gc.set_font(font_1)
    gc.show_text_at_point(f"font_1: weight={font_1.weight} style={font_1.style}", 20, 60)
    gc.set_font(font_2)
    gc.show_text_at_point(f"font_2: weight={font_2.weight} style={font_2.style}", 20, 20)

Which produces:

We would expect the second line to be bold.

Most backends suffer from this: Cairo does not, and a number of backends ignore bold/italic

[corranwebster]

Potential strategy for fixing this:

• change the weight attribute of a Font to instead hold a weight value of 100, 200, ..., 1000 stored in standard constants.
• if we see a weight of BOLD, then assume bold (700) and issue a deprecation warning
• if weight is normal (400) and we see a style of BOLD or BOLD_ITALIC then assume bold (700) and issue a deprecation warning
• otherwise weight is just passed directly to font queries as a numeric value
• for font parsing, continue to only recognise bold for now
• for backends that don't use font queries replicate the above logic. There may be some backends which can't express weights other than normal and bold (eg. Pyglet/OpenGL, Cairo) and so some basic heuristics may be needed (eg. > 500 is bold)

We might possibly keep the select_font API using the older style (although it expects text "bold", "bold italic", etc.)

[corranwebster]

Interestingly enough, Cairo now has a distinction between "toy" font specifications (such as "serif", bold, italic, size) and "real" font selection which uses a "font backend". Their solution was to have two subclasses of a base Font class. I don't think that will work in this situation. Note that PyCairo can't access the "real" font selection system because the backends aren't wrapped in a useful way.