Better method for accretion disk rendering

[bgmeulem]

Currently, I manually set a max radius on which I sample points. It's rather unclear what's supposed to happen when ghost images pass through. I assume a perfectly opaque accretion disk with sharp cutoff at the max radius.

I'm not planning on implementing actual ray tracing, scattering functions, absorption etc (have a look at the SKIRT project if that's if interest to you), but I can probably figure something out that works better then what I do now.