vector sample_sphere_shell_uniform(vector u, float alpha)
Three numbers between 0 and 1.
The inner radius to be bounded by. A number between 0 and 1.
Returns a vector of length < 1, based on
Given uniform random
u vectors of three values in /vex/functions/0,1), and a number in [0,1, the returned vectors will be
uniform random and continuous with respect to
u inside the unit sphere shell with the inner raidus alpha.