The grid units are responsive to the existing grid scale, subdivisions, and overall blender UI scale settings. Further options are added to the viewport overlay menu configuring a scale multiplier for the unit labels, as well as their tint and opacity. The addon preferences define defaults for new scenes and take effect on next startup. Font/unit texture configs take effect immediately.

The unit cards use lookups on a regular png texture; you can copy/modify this atlas to contain any glyphs/representation you want, provided the size remains at 512x512 and glyphs are divided into a 5x5 grid. The addon prefs allow you to set a path to this custom texture.

The unit labels have an algorithm that maintains visibility and avoids crowding based on window/viewport pixel size and viewport camera properties.

Units are drawn in batch, with limiting of how many cards are drawn based on view frustum intersections with the perspective/ortho grid, to maintain high performance.

All versions are available in the product files, just be sure to grab the latest one unless you actually need to go back for some reason.

Changelog

v4
* Allowing the overall viewport show/hide toggle to control the grid unit settings, keeping it more in line with how the other viewport overlay controls work.

v3
* Adding support for length preference to be reflected in the labels used, e.g. centimeters, inches, meters, feet.
* Fixing labels for imperial unit system.
* Evened out ortho vs. perspective scale bump.
* Added a hack for *imperial units* to mimic the sort of major grid line jumps the Blender grid is doing at various scales; it's a confusing set of grid lines to begin with, but this addon's labels need to follow them.
* Fixing a draw issue with +Z/-Z axis orthographic at very small view distances.

v2
* Mac OS X support, better cross-platform shader code.

v1
* Initial release