Feature request: set mathtext fonts via the object oriented API

[ngoldbaum]

As far as I can see (and according to the documentation), the only way to set the font of mathtext snippets in plots is via the mathtext.fontset rcparam.

It would be nice if there were some way to control the fonts used for mathtext rendering without messing with the rcparams system. Maybe the font could be chosen based on the FontProperties instance associated with the Text object? To make a concrete example, it would be nice if the y label for this plot were rendered using a serif font, like the rest of the plot.

import numpy as np
from matplotlib import pyplot as plt
from matplotlib.font_manager import FontProperties

fig, ax = plt.subplots()

fp = FontProperties(**{'family': 'stixgeneral'})

im = ax.imshow(np.random.random((800, 800)))
cb = fig.colorbar(im)
cbax = cb.ax

ax.set_xlabel('x label')
ax.set_ylabel(r'$\rm{y\ label}$')
cb.set_label('colorbar label')

labels = ax.xaxis.get_ticklabels() + ax.yaxis.get_ticklabels()
labels += cbax.yaxis.get_ticklabels()
labels += [ax.xaxis.label, ax.yaxis.label, cbax.yaxis.label]

for label in labels:
    label.set_fontproperties(fp)

plt.savefig('test.png')

For additional context, see #6514 and my message to the matplotlib-devel mailing list: https://mail.python.org/pipermail/matplotlib-devel/2016-May/000454.html

[zblz]

Can this be achieved with an rc_context withouth touching user rcparams?

with mpl.rc_context(rc={'mathtext.fontset':'stix'}):
    fig, ax = ....

I agree it would be nice for a way to set both text and mathtext fonts as a group so they are consistent, and currently it is not completely obvious.with mpl.rc_context(fname='mpl.rc', rc={'text.usetex': True}):

edit: nevermind, I saw you already mentioned the context manager in the email.

[ngoldbaum]

While it's true that this issue can be dealt with using a context manager (ping @mdboom and @WeatherGod, let's move discussion to this issue since it has a clearer call for action), I think that's less useful than being able to programmatically customize fonts using the FontProperties interface. Keep in mind that I'm thinking in the context of yt, which has a several thousand line wrapper around matplotlib, so saying "use the context manager" is more complex for me since the plotting code is spread out over several modules (since I make use of inheritance to avoid code duplication) and many different functions.

Here's a couple reasons to justify why I want something besides the context manager approach:

1. It provides a uniform interface for setting fonts for all text.
2. I might not know that the text being displayed by a given Text object (for example, a label in a plot) is MathText or regular text - so I need to implement two very different code paths, one that sets an RC param as the plot is drawn, another that sets the FontProperties at some point before the plot is drawn, just to ensure that the two kinds of text have consistent fonts.
3. This isn't isolated to axis and colorbar labels, since the tick marks for axes that have logarithmic scales are rendered in MathText by default, so I also need to have special handling for tick label fonts as well.
4. It violates the principle of least surprise to silently ignore the font settings from the FontParameters associated with a text object, just because the text being displayed contains a MathText expression.

[mdboom]

The tricky bit here is that math rendering requires a particular set of fonts that work together (the "fontset") rather than a single font. There are only a very small set of such fontsets supported. So we'd need to add a new property to FontProperty to set the fontset and ignore all others. Not really an ideal API either.

[ngoldbaum]

That actually sounds nice to me - I could do:

fp = FontProperties(**{'family': 'stixgeneral', 'mathtext-fontset': 'cmr'})

And non-mathtext text will use 'stixgeneral', while mathtext uses computer modern.

[WeatherGod]

I'll be +1 to that idea, but I get the point that it isn't ideal. As a
user, I say "use this font", and that font doesn't get used... I would be
rather surprised. It isn't immediately obvious that I would need to specify
two parameters to set my fonts. The font-handling system is probably due
for an overhaul soon, I think.

On Wed, Jun 1, 2016 at 1:28 PM, ngoldbaum notifications@github.com wrote:

That actually sounds nice to me - I could do:

fp = FontProperties(**{'family': 'stixgeneral', 'mathtext-fontset': 'cmr'})

And non-mathtext text will use 'stixgeneral', while mathtext uses computer
modern.

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[zblz]

A possible alternative would be to set mathtext.fontset by default to None, and write some logic that selects the fontset depending on the FontProperties of the surrounding text, trying to get as good a match as possible. If mathtext.fontset is specified, then we go with that no matter the FontProperties. I imagine that this would be closer to most user's expected behaviour.

However, in the case specified by @ngoldbaum ('family': 'stixgeneral') the fontset chosen would probably have to be stix rather than cmr...

[efiring]

On 2016/06/01 10:51 PM, Victor Zabalza wrote:

A possible alternative would be to set |mathtext.fontset| by default to
None, and write some logic that selects the fontset depending on the
FontProperties of the surrounding text, trying to get as good a match as
possible.

Looking at surrounding text? That sounds much too complicated and magical.

[anntzer]

Closed by #18145.