Add a single setting to scale all font sizes

This was originally proposed for vegalite and altair in https://github.com/vega/vega-lite/issues/1714 and https://github.com/vega/vega-lite/issues/6988 and reccomended by @domoritz to open an issue here instead.

Currently, it is cumbersome to scale ip all font sizes since it involves setting many different parameters individually, for example:

spec.width = 800;
spec.height = 500;
spec.config.axisY.titleFontSize = 14;
spec.config.axisX.titleFontSize = 14;
spec.config.axisY.labelFontSize = 16;
spec.config.axisX.labelFontSize = 16;
spec.title.fontSize = 20;
spec.encoding.color.legend.titleFontSize = 15;
spec.encoding.color.legend.labelFontSize = 15;
# facet headers fontsize also needs to be set individually now

Providing a shortcut for scaling all these parameters would be highly convenient from a usability perspective, particularly as a setting that applies to all plots (similar to setting a default theme), but also (less importantly) for individual plots. For what it’s worth, this setting is available in other high level plotting libraries such as seaborn (sns.set_theme(font_scale=1.5)) and ggplot (theme_set(theme_grey(base_size = 18))).

I believe this feature is especially important since the the default font sizes in Vega are quite small. If possible, it would also be great to also consider an increase of the default fontsizes to ~1.2 times the current size, but I understand if this default is no longer amendable to change from suggestions.

I believe all the defaults are listed here for future reference https://github.com/vega/vega/blob/main/packages/vega-parser/src/config.js#L82-L129=

Please:

• Check for duplicate issues. Please file separate requests as separate issues on GitHub.
• Clearly describe the goal of the feature request. Why is it needed?
• Describe an envisioned solution. What do you want the new behavior to be?
• If applicable, share mockup images or links to examples illustrating the desired output.
• If applicable, share JSON spec designs for how the behavior would be made available in Vega.

[kanitw]

FYI, for

spec.config.axisY.titleFontSize = 14;
spec.config.axisX.titleFontSize = 14;
spec.config.axisY.labelFontSize = 16;
spec.config.axisX.labelFontSize = 16;

you can just do

spec.config.axis.titleFontSize = 14;
spec.config.axis.labelFontSize = 16;

So it’s a bit less tedious.

[joelostblom]

In Seaborn’s set_theme function, you can change the scaling of all plot elements (so text, axes, markers, etc) via the plotting_context param, and control the size of just the text with the font_scale param. For ggplot I am unsure if there is an option to control the size of all plot elements, but base_size can be used to scale all text as above.