Quake

I have also done Quake mapping and even done an editor for fun[0] some time ago :-P. You are supposed to stick to the grid, the crate texture is sized so that it fits perfectly on the grid. If you go off the grid things become a bit harder, but this is why pretty much everything on Quake is axis aligned :-P. It is ridiculously simple to make stuff actually. About rotation, most editors that people used even in the 90s had support for texture locking for both translation and rotation. id's original editor was very primitive though, but later editors like Worldcraft and Radiant had those features. WRT. texture coordinates, they are converted to U/V (or actually S/T) pairs, but it happens quite late during the edge span rasterization. You can see the inner rasterizer loop here[1] where it draws an edge span and performs a linear interpolatio