But wait! Divide by zero? Oh. Whew.
But doesn’t projection require dividing by the z coordinate? If -1<=z<=1, won’t we get divide by 0?
Ah, but it’s really the w coordinate we divide by, and it’s positive definite!
- The original perspective transformation puts a vertex’s z value in w
- Since hither<=z<=yon for vertices that don’t get clipped, w is positive definite (modulo sign convention for hither and yon)
Hence, no worries on that front. All the z=0 vertices will get clipped before we divide out the homogeneous coordinate.