The original code was commented on.
Unlike blender 2.79, the grid units are now displayed only when RV3D_VIEW_IS_AXIS.
The visible subdivisions in the grid are made by the GPU and depending on the pixel.
The code used here only mimics this behavior and adds a bit of overhead.
Reviewers: fclem, campbellbarton
Subscribers: FloridaJo, zlsa, rl.amorato, EitanSomething
Differential Revision: https://developer.blender.org/D4325
859f2561c8