Rough Glass Shadows

Hello everyone,

I was trying to find a solution but without luck. So, my question is about Cycles: is it possible to get blurry shadows from a rough glass material (without Compositor)? If yes, then, how to control the blurriness?


Have you considered changing the light properties instead of the material? I see you might be using Nishita Sky, so it would be increasing the degrees of the sun size. Play around with that parameter!

Hope it helps :slight_smile:

I don’t need to blur all shadows. I’m looking the way to make the shadows from rough glass materials more physically correct. So, you solution doesn’t help :slight_smile:

No, can’t be done with brute force alone. You’d need to bump the normal of the glass shader (or roughness? not sure) and rely on caustic transmission (no transparency tricks) with millions of samples with the Cycles engine. Luxcore engine has better ways to do caustics, but loose out on some other goodies.

Caustics turned on, Glass shader alone, Bump added… the shadow becomes fully opaque.

Samples? You need millions, maybe trillions of samples for a path tracer like Cycles to resolve this to something close to sharp. An image is going to take years to compute - so not an option to brute force it.

CarlG, I understand that it’s not possible to achieve nice results. But there is no anything that resembles that the glass is transparent: Glass shader alone is treated like a completely opaque material (look at the shadow from the yellow glass).

Looks like you don’t have transparent shadows enabled

And you can’t. For shadow rays;
if you use transparency, you can’t control blurriness.
if you use translucency, you get full diffusion.
if you use refraction, you should be able to get the blurriness but at tons and tons of samples.
Note that for refraction, you can use geometry/incoming as the normal to avoid bending light and still have “rough transparency”. I often use this trick for “thin geometry”, i.e. if I want rough highlights from backlight, but I have never had the need to try this for shadow rays.
What is the material you want to create, and do you have a real world reference that show the effect?

Edit: Actually, for very rough glass you can get away with refractive caustics, and even normal adjustments will show up. Since caustics is a global setting, you now have to decide to make all materials caustics based with the problems that arise from that. I never have caustics enabled and make my materials accordingly by faking some light transport and suffer the accuracy. Never had a complaint about it though.

They are enabled. According to the tooltip, that setting affects only Transparent shader.

OK. I’ve experimented a little bit more and it looks like it makes sense. Thank you!