Yet another fake caustics approach

[maru]

Here is the idea:

1. Place 2 planes: A - bottom, B - water surface - it has to be 3d water (not sure if bump map works)
2. Apply dark, diffuse material to bottom
3. Apply water material to water surface, with caustics enabled, nest this material in a rayswitch so that it is visible ONLY to GI
4. Place sun so that it shines directly from above (in zenith)
5. Switch engine to VCM
6. Set resolution to square
7. BAM! You end up with nice caustics map
8. Open it in PS, desaturate, inverse colors, save

9. Slightly modify the scene: change bottom color to some lighter one, disable caustics for water
10. Change engine back to standard progressive
11. Create a 3rd plane, between water and bottom
12. Apply pure black material with opacity map to the 3rd plane - as opacity map use (surprise) the caustics map we saved earlier
13. Nest the pure black material in rayswitch, make it visible ONLY to GI rays

14. Render

With SSS you can even turn those into VOLUMETRIC CAUSTICS.

I know this has a lot of flaws and probably can't be used for animations, but this idea was in my mind for some time now. Maybe someone will find a use for it, who knows... :)

[ikercito]

Will give it a try this evening. I really needed this, thanks for posting! :D

[Juraj]

. BAM! You end up with nice caustics map

Actually I have so far tried using VCM in very simple scenarios multiple times. Even letting it run 24hours on my 40thread Xeon, the render was noisy and the map was blurry. It does hardly produce the kind of beautiful, super clean and crisp caustic that Photons can generate. It's not even comparable.

But this step should be replaced by Caustic generator plugins, of which there is plenty on internet, most of them free. This will significantly speed up this approach.

[Slazzo]

The problem with it beside it's fakeness, it's that caustics are focused light and has to be brighter than the light that will hit the surface directly, but in your case you end up with very dull/unrealistic looking effect. Yet the old projection map on light will do better.