Alpha below which impostor pixels are discarded.
Views per atlas side (octahedral mode). 8 = 64 views.
Only bake views from above the horizon (better resolution for things seen from the ground).
'octahedral': frames × frames views over the (hemi)sphere; the quad shows whichever view is closest to the
camera direction, so the object turns correctly as you walk around it.
'billboard': one side view on a quad that turns around the vertical axis. Cheaper to bake, 4× less memory per
view, fine for symmetric objects far away.
Atlas width and height in pixels. Each view gets size / frames pixels.
How an impostor is baked and drawn.