Scatters rays that collide with arbitrary lines (represented here as blocks), then builds a light volume from the updated rays.
It already has backface culling, but I am definitely open to any and all optimization suggestions! I have another version, a bit more complex, where the boxes know if they are hit by light.
Uses Line-Line Intersection by Ryan Alexander. Inspired by a forum post by TheAustech on The Chaos Rift.