Comment by zamalek

Back in the day I was writing a liero clone, and came up with a neat scheme for pixel-perfect collisions (probably serendipitously, no claims it's unique). A 64bit integer can be seen as an 8x8 mask. You can pixel shift it up and down by simply bitshift left or right by 8n bits. Pixel shift left and right required more instructions; if I was to write it today I would probably store an additional rotated version instead (as that would then effectively pixel shift left and right with bit shifts).

You then have the terrain chopped up into these 8x8s too, and can then do a collision test with at most 4 of them with the 1 character/entity mask.