vector sample_sphere_cone(vector center, float maxangle, vector u)
Direction in the center of the cone. This does not need to be normalized.
Maximum angle, in radians, away from
center that any sample of the cone
will be, so long as all
u values are between 0 and 1.
Three numbers between 0 and 1.
Returns a vector of length < 1, based on
Given uniform random
u vectors of three values in [0,1), the returned vectors will be
uniform random and continuous with respect to
u inside the unit sphere,
in the volume within
maxangle of the direction indicated by