Screen relative movements are inaccurate

[markwheeler]

screen.move_rel(0, 0) causes things to move a little on both axes. It seems like all relative movements are slightly offset.
Similar error in screen.line_rel()

[tehn]

@markwheeler

indeed there's a bug: https://github.com/monome/norns/blob/master/matron/src/hardware/screen.c#L255

this command shouldn't have the 0.5,0.5 offset. and many other similar bugs can be fixed.

so the issue is the "center" of the pixel is offset by 0.5,0.5. if you use 0,0 it's the "corner" of the pixel and the color will be darker as a result of anti-aliasing an off-center coordinate.

so it seems when typing up the lib i blindly applied this rule to a bunch of stuff that wasn't supposed to have it applied. particularly the _rel commands.

[markwheeler]

Ah yep I see. Looks like this applies to rect and arc also. I would expect screen.rect(0,0,1,1) to draw the top leftmost pixel but I have to offset by -0.5 on both axes to get it there.