How to make refractive caustics (water)?

Download the example scene. (Created with 3ds Max 2022 and Forest Pack 7.1.2)

What is a caustic? 

Most artists think of caustics as the light that gets focused through glass or water. But, for the people in computer graphics: A caustic is any lighting contribution that goes from light source to specular (reflective or refractive), to diffuse surface, to eye (or camera).
 

Read more in our blogpost "What are Caustics and how to render them the right way".

Caustic solvers in V-Ray

In V-Ray, there are two ways for computing caustics - Photon mapping (old) and Progressive caustics (new). 

As of V-Ray 7, Caustics (Photon mapping method) can be calculated on the GPU.

In this article, we will focus on using the Progressive caustics solver. Bear in mind that the feature is still work in progress. If you happen to find an issue, please report it. Contact Chaos Support.

 

Requisites

To produce caustics, generally, you need three things:

• A refractive VRayMtl material with affect shadows turned off. 

  To get accurate results, VRayMtl's "Affect Shadows" option, which is designed to create a simple caustic effect, must be turned off. 

• A light source

  For best results - a small bright light source, which  will produce sharp caustics.

• An object to catch the caustics

   

Setup

In this tutorial, we will make swimming pool caustics. 

• Geometry

  We've created a pool geometry to catch our caustics and a plane for our water geometry with a VRayDisplacementMod for extra realism.
   

The water can be displaced via a Noise texture, but any procedural wave texture will work. Both closed (box) and open (plane) water geometries will produce caustics.

• Materials

  For the water material, we will use VRayMtl with the Water preset. Remember to disable Affect shadows.
   

For the other objects, you can have any materials of your choice. You can use, f.e., the pool tiles from the Chaos Cosmos library.

 

• Settings

  As the calculation method, choose Progressive (WIP). This method doesn't need much setup, except using the Progressive Image Sampler.

   

  

  You can modify the multiplier of the caustics in the Expert settings in case you wish the effect to be more visible.

• Lighting

  For the light source, we'll use a VRaySun. Make sure the Photon emit radius parameter covers the whole area of the pool. The area outside of the radius will not be calculated.
   

Other small and bright light sources could also work.

• Result

  Adjust the angle of the light so you can achieve different caustics results. 

Note that for the caustics to appear, a few passes must render first.