The perspective matrix now as in glm (because the near frustum plane was
wrong). So there is a factor "2" on the component w and the skybox must
be changed in consequence.
Former-commit-id: 09dd049c177532b9ace34a5a60b1b96014652297
Planes are changed to ax+by+cz=d, so the plane with normal (0, 1, 0) and
distance 1 is y=1.
Operators == and !=.
Former-commit-id: 5267a183a9e6fb490de099d536ea2f64558f674d
Gawaboumga