Flector
Builds the flector (fx, fy, fz, fw), unitized and zero-sanitized.
The mirror's normal norm √(fx² + fy²) divides out, so a constructed flector always stores a unit normal — what makes fw exactly half the glide distance and |fz| the mirror's distance from the origin. Signed zeroes sanitize to +0.0. A normal norm that rounds to zero at the SCALE quantum describes a mirror at infinity, and no flector is built.
Parameters
fx
The e423 component.
fy
The e431 component.
fz
The e412 component.
fw
The e4 component.
Throws
when the mirror's normal norm rounds to zero.