Trying to do Caustics (reflected light from a Gold object) and not having much luck.

Any good tutorials on this? I couldn't find much in the docs that helped.

-Craig

By the way, I found my old video tutorial on Caustics by Peter Bowmar and have followed an old posting on OdForce and I still can't get it to work. I know I have done this in the past and am wondering if something is broken…

This is 8.1.704 running on XP.

-Craig

I did a video on caustics back for 6 or 7 (can't remember). However, as I am avoiding sleep, here's an example .hip file.

Basically, you assign a Photon Plastic shader to the Vase, set Specular prob to 1, set the rest to 0.

ASsign another to the ground, diffuse only.

Calc your photons in the Mantra ROP.

Render using the GI Light ROP.

The part I always forget is assigning the photon shader to the ground…

Cheers,

Peter B

Hi Peter!

Thanks a lot. I actually found your tutorial a while ago and it seemed like I was doing everything correctly. I went back to an old H7 version and it seems like it works properly. Could it be broken in H8? Or at least the version I am using (8.1.704)?

I can't seem to get H8 to render out a pmap larger than 1 KB.. But H7 does it fine.

Maybe it's just me.

How's it going over there? How are you liking London? Hopefully we can do lunch in Soho again soon!

-Craig

Also I am finding I have to crank up the “Global Tint” in the Irradiance Tab to really high numbers (>100) to really see the Caustics. I am using “No Irradiance”, but this seems to be the only way to brighten the photons up.

Or am I missing something obvious?

Again, I am doing this in H7…

Thanks,
Craig

Hey Craig,

Its not uncommon to crank the # Photons cast to a huge number like 50m. The more photons that “stick” will brighten the image up and improve the quality of the caustic.

I'm still kind of frustrated that you can't “point” the photon casting in a specific direction and cone angle. So many photons are wasted in most scenes as a result. Realistic? No, but we're making movies (or games) dammit!

Cheers,

Peter B

It seems like I get different results in the size of the photon map if I change the Cone Angle of the light, plus Jason's response to my other posting about Photons says that the Cone Angle does control where photons go, so perhaps we do get some control.

In my case a huge majority of photons are going to get reflected off into nowhere, so a huge number is still needed to get decent caustics.

-Craig

PS: By the way, I am using Houdini 7 because 8.1 seemed to not work correctly for this. Is this just me?…

Hi Craig,
I did this in 8.1.866, worked OK for me. Also, I believe that the cone angle does affect it but what happens is the photons cast in the “non cone angle” areas have 0 energy, which still “wastes” them IMHO. I discussed this with SESI a long time ago, so perhaps it changed
The problem is there is a relatively low upper limit (2 billion or something) on the total number you can cast so any with 0 energy don't contribute to the caustic look, meaning the sampling isn't as nice.

Cheers,

Peter B

Wow, good point. I don't want to shoot “blanks”!!

If they can make them emit only where you want them to be emitted this process would probably get much faster and higher quality!

Thanks so much for your help!

-Craig