…ndefined (older browser), or <= 1 (actual low-res screen)

- removes translate(0, 0.5)
- uses lower-precision numbers (#2270, #2234)

closes #1445

…anslation we apply on lower DPI screens

The hexbin transform used a hardcoded ox=0.5 to avoid Math.round(.5) ties
on the right edge, but this caused floating bins on the left odd rows.