Most resources seem to suggest that points on the clip planes are also
inside the frustum, e.g.: https://www.cubic.org/docs/3dclip.htm
This seems to resolve some rendering issues in Grim Fandango in OpenGL
mode where the screen remained black. This was because of quads being
drawn with their vertex positions exactly on the clip planes.
The previous clipping implementation was problematic especially when
clipping against the near plane. Triangles are now correctly clipped
using homogenous coordinates against all frustum planes.
Texture coordinates and vertex colors are now correctly interpolated.
The earier implementation was just a placeholder.
This code has also been optimised to be much more memory
friendly by removing a _lot_ of extraneous copies. The result
is that, when profiled, it's around 8x faster than the previous
implementation.
Co-Authored-By: Ali Mohammad Pur <ali.mpfard@gmail.com>
