the fragment shader, cubemap textures are accessed using a samplerCube
texture coordinates, [s, t, r]T are
used in conjunction with the samplerCube
texture coordinate is interpreted as a direction vector from the centre of the
cube. The direction vector is normally
in world coordinates.
line defined by the vector and the centre of the cube is extended to intersect
one of the cube faces.
image that corresponds to that face is then accessed at the location of the