> a very good performance optimization is not to try to reject segments on the X axis in the shader. Rejecting segments which are below or above current pixel

> a very good performance optimization is not to try to reject segments on the X axis in the shader. Rejecting segments which are below or above current pixel boundaries is fine. Rejecting segments which are to the right of the current pixel will most likely increase shader execution time. Thread groups are generally rectangular IME--nv is 8x4, others 8x8. So it doesn't make sense to distinguish X from Y in this respect. But yes, you do want a strategy for dealing with 'branch mispredictions'. Buffering works, and is applicable to the cpu too.