Speculating here based on my experiences in the past building my own physics engines: running along a wall could speed you up a little bit depending on how they’re handling “keeping you outside the wall”. One common/simple way is to apply x1 = x0 + v*dt, calculate collisions after the moment calculation, and then fudge your position back to being inbounds. If I recall, Q1 used simple bounding boxes on all of the entities as well and there’d probably be some (pardon the pun) corner cases in the “keep out of the wall” algorithm.