Fontconfig Error - Fonts fail to render

[kykrueger]

Hello,

I am having an issue with saving altair charts after doing an install with conda on a miniconda3 docker image.
The versions I am using are:
altair 4.1.0 and
altair_saver 0.5.0

This error is thrown when the chart is saved:
Fontconfig error: Cannot load default config file

The resulting png when using the Window Rank Example then contains square symbols instead of the expected characters.

I expect this is due to the fonts in this docker image being installed different than other systems, but other packages seem to be able to handle this and find the fonts which are indeed available in the underlying Debian Image.

This issue is not present when saving to html, but with png, svg and pdf.

[kykrueger]

It seems like the problem is a part of altair-cli

[kykrueger]

A bit further down the rabbit hole, and canvas seems to be responsible.
Shashank3736/captcha-canvas#20

[kykrueger]

Adding fontconfig to my docker image fixed the problem.
I did this with
apt install fontconfig