Additive blending for world-space billboards. The billboard's RGB, scaled by its own alpha, is
added to the framebuffer (no depth write, like the other transparent modes), so overlapping
billboards stack and brighten — world-space embers, sparks, muzzle flashes, and light shafts.
Additive blending for world-space billboards. The billboard's RGB, scaled by its own alpha, is added to the framebuffer (no depth write, like the other transparent modes), so overlapping billboards stack and brighten — world-space embers, sparks, muzzle flashes, and light shafts.