Is it possible and easy to do that? I don’t understand the code enough to make it happens. It would be great for vertical shmups in Mame/FBA.
Using the usual horizontal shader and rotating the picture (first in Mame GUI then in Retroarch to make the scanlines vertical) has its issues and is a bit annoying to do all the time.
Unfortunately, the scanlines in that shader are a bit more intensive than most, so you can’t just swap the .x/.y swizzles and have it work properly. You could apply a rotation matrix to the whole thing, but that brings up a host of issues of its own.
Tbh, I think the double-rotation thing you described is going to be your best bet.
I worried about this issue a while ago. For what it’s worth, regular MAME gets the scanline direction right automatically if you use my shader with SDL+GLSL.
Thanks. Seems there is no easy solution then for retroarch atm.
Rotating Mame GUI then Retroarch is OK for scanlines but if you want to use crt-geom with the curved tube effect, it gets rotated too (base of the screen on the right side).