Crumb
c/blender · by nemopy@lemmy.zip · 35d

The Cycles Principled BSDF will support dispersion

https://projects.blender.org/blender/blender/pulls/162041

The patch was accepted and merged to main as of today 2026/08/18

12 points · 6 comments · view on lemmy.world

6 Comments

TacticalToothbrush@discuss.tchncs.de · 4 pts · 35d (3 replies)

Heck yes! no more white noise + IOR range trickery.
People will go nuts when they put in full caustics.

edit: tried it with 2026-08-20 build, and it's okay.
feels more noisy compare to old hacky way.

Hadriscus@jlai.lu · 2 pts · 35d (2 replies)

I don't usually render dispersion, but the few times I've done it in the past was by mixing several refraction bsdfs with varying IORs and colors. How do you use white noise for the same effect?

TacticalToothbrush@discuss.tchncs.de · 3 pts · 35d (1 reply)

I don't usually do dispersion either. I forgot the detail and have to refresh my memory by building it.

This node setup is a simplified version of method in the video linked below basic dispersion setup

https://www.youtube.com/watch?v=lEPZ1IUkoB4

In this video, the author goes into detail as to why using white noise is superior - the dispersed colors are continuous.

And with this glorious feature update (assuming it will land in 5.3) we can skip all the riggamaroo demonstrated in the video and get even more physically "accurate" result.

Hadriscus@jlai.lu · 1 pts · 35d

Cheers, I'll take a look. From your capture I'm not sure I understand how it would create a continuous rainbow. I would expect homogeneous color noise. I suppose the video answers this

Hadriscus@jlai.lu · 3 pts · 35d (1 reply)

That's good news, maybe Cycles doesn't need to go full spectral after all if that sort of effect has special handling.

nemopy@lemmy.zip · 3 pts · 35d

Exactly my thoughts.
I checked the spectral Cycles branch devtalk thread and it seems to be pretty much dead, and this patch looks like the final nail in the coffin.
I hope the work and effort of the community contributed in any way to this, I believe the branch ended in a point where there were too many issues too hard to deal with.

Some more good news is that according to someone who knows more than me presumably (u/Eary in the devtalk forum), I quote:

we can avoid the previous community branch attempt’s complication around E white point and D65 white point CAT adaptation, and we also make the architeture more physically meaningful in a way that the light spectrums can be real known ones with filter, instead of completely arbitrarily uplifted from RGB. [...] This is actually quite elegant

Though they also mention that this implementation has its drawbacks in some specific edge cases and assumptions taken (hardcoded stuff), which would need multiple presets to handle all of them.