Use wider cells for proportional fonts
Every once in a while, people end up with proportional fonts in their terminals (e.g. due to some misconfiguration such as Red Hat 1715761). This is hardly readable due to the heavy overlap between letters.
In order to mitigate the problem, and make it easier to fix from within gnome-terminal, I think we should use wider cells in these cases, to (mostly) avoid overlaps. That would still look ugly, but would be much more usable.
Currently the width of a cell is the average width of the ASCII letters (weighted heavily towards the width of the space character, to work around caching ligatures), measured in vtedraw.cc
font_info_measure_font()
using the sample string defined in VTE_DRAW_SINGLE_WIDE_CHARACTERS
.
It would be better to go for the maximum of widths, or at least a formula that favors larger numbers (such as quadratic/cubic mean, or 90th percentile, or a weighted average of the min and max values, or just stuff more "mmmMMMwwwWWW" characters into the sample string, etc.).
On a technical note: It could be desirable to separate the width measurement from the caching of glyphs.