Vertex preview (should work for 2D and 3D now)

I tried to copy the algo from softgpu, and it has broken 3d also, so may be related... but I'm probably doing something wrong.  Also, used a fixed z value.

~~Well, I think the 2d may be broken in some cases too (probably still need to apply offset or something?)~~

But at least it works.  You can see which parts of the texture are being used and etc.

~~Could use some help on the coordinates...~~

-[Unknown]