LuxCoreRender Forums

I'm getting problems with caustics flickering - is there any sort of random seed?

Luxcorerender produced really nice caustics but sometimes "they seem to move erratically in an animation instead of linearly"

I don't think it's fireflies - it seems the caustics jump around from one spot to another between two frames only 1 frame apart but the material creating the caustic hasn't changed that much...

(Examples resized and edited to small size):

In this short video - the caustics on the sand are smooth and move in relation to the surface of the water. this is how I would expect it to work. But the caustics on the surface of the water are all over the place and don't move smoothly. In the end of the video looking into the water the caustics on the bottom of the water are all erratic and "flashing" In this wave video - I would expect the caustics to move in relation to the water waves but they jump all over and it looks like they are flickering. (I read the other thread on flickering video and this seems different?) This is large areas of flickering not just smaller spots...

These ARE denoised - but I compared the non-denoised and the non-denoised also has the caustics flickering erratically.

Render engine: "BIDIRCPU"
Sampler: "METROPOLIS"
Light: Sun
Environment: Sky

The flickering caustics are created by SDS paths (specular-diffuse-specular). They are either impossible or very very hard to find for Bidir.
You will need to use the Path engine with light tracing and PhotonGI caustics cache to render them.

Thanks for the reply...

Interesting... I always thought Bidir produced more desirable "pronounced" caustics...

Would it be correct to say PhotonGI cache just speeds up the caustics or is it required to create them?

Is there any sort of random seed or trick to get them consistent between frames on an animation? Or just switch to Path + PhotonGI?

zukazuka wrote: Sun Apr 26, 2020 3:46 pm Interesting... I always thought Bidir produced more desirable "pronounced" caustics...

If the appearance of a caustic would change between engines, it would be a bug (aside from noise level or existing/non-existing).

zukazuka wrote: Sun Apr 26, 2020 3:46 pm Would it be correct to say PhotonGI cache just speeds up the caustics or is it required to create them?

The PhotonGI caustic cache is the only tool in LuxCore that can render SDS caustics.

zukazuka wrote: Sun Apr 26, 2020 3:46 pm Is there any sort of random seed or trick to get them consistent between frames on an animation?

You mean in Bidir? You can render each frame until it is noise-free, which probably takes a few months per frame judging from the videos you posted.
Or you can try to make them non-SDS caustics, by using shader tricks, or fake them entirely.