LÖVE

If you set a note on "Quarter", "Start" or "Stop" it's another square to draw, the user could potentially slow down the program and I'd like to avoid it; and now that I know how spritebatches' image IDs work, I find them nicer

okay. It's just that drawing the whole grid only at the start means that you get lines being erased when you erase notes, unless that's a bug.

That's a bug... I don't know why, but in some PCs either lines or squares are 1px down (or maybe they're 1px up on the other PCs), so deleting them (by drawing a 5*5 black square) erases a line too