Dual ParaboloidMath Cheat Sheet
How to map (rx,ry,rz) unit vector to
(s,t) texture coordinate in [-1,1] range
Reverse mapping: (s,t) to (rx,ry,rz)
rz = (-1 + s2 + t2) / (s2 + t2 + 1)
rx = - 2 s / (s2 + t2 + 1)
ry = - 2 t / (s2 + t2 + 1)
rz = - (-1 + s2 + t2) / (s2 + t2 + 1)