I find that the file is not at all messed up, coordinate wise (see attachment).

One technicality though about brush definitions:

While I agree that it is all about vertices, it is also about half-spaces, i.e. plane definitions. 6 plane definitions (equations that evaluate to >0 for outside or <0 for inside) make up a hexagonal (cube, bush whatever). Each plane is defined via three vertices in the map file. That is its weakness (and maybe room for extension).

Here is the catch as far as I understood:

- you can of course manipulate your blender cube any way you like

- that does not always leave you with planes since your manipulated four vertices are no longer guaranteed to lie on a plane

- the blender exporter takes (I guess) the first three vertices per quad (since our cube has 6 quad faces)

- our UFORadiant loads three vertices per quad (it cannot do any other since it only has these three per side)

- it sets up a plane equation (presumably) and takes into account the other planes

- the fourth point gets either interpolated along the lines of three other plane equations or some existing point gets taken into account

That's the mess we're in. Nothing to do with coordinates really. This will sound monstrous probably:

My question is: How hard is it to change the brushes definition to two triangles instead of one? It would break up each quad into two, will leave us with easier phong interpolation, etc.? Probably no longer is a Q2 engine, then