fix rectangle normals

[ffreyer]

I added extra coordinates to Rect3D. Now each face has its own set of coordinates, and normals act as surface normals.

[ffreyer]

Btw, shouldn't minimum and maximum return the true minimum and maximum?
For example, with r = Rect3D(Poitn3f0(0), Vec3f0(-1)) you currently get minimum(r) = Vec3f0(0).

[SimonDanisch]

Oh, good point :-O I guess, I kinda assume, you dont have negative widths... But then again, it's not enforced by the constructor!

[ffreyer]

I think there are situations where it's convenient to use negative widths. Say you want to add a floor rectangle in some 3D plot. Then it's more convenient to write Rect3D(Point3f0(0), Vec3f0(1, 1, -0.2)) than Rect3D(Point3f0(0, 0, -0.2), Vec3f0(1, 1, 0.2)) imo.

[SimonDanisch]

It is, but we may want to rewrite that in the constructor to still end up with positive widths, I suppose