Fast Caustics with Thea Presto


by | May 31, 2016 | Tips | 17 comments

This article will show you how to achieve fast caustics, using Thea Presto Engine.

Lights need to have a surface area in order for Presto to produce caustics and the Sun is not one of them. It is so far away from the scene that it can be thought of as a point light.

On the other hand, the Unbiased Render Engines (TR1 / TR2) are able to produce accurate caustics, even in extremely difficult situations and this is something quite challenging to port to GPU. That is for the time being and until our next advance!

But let’s see how we can use this technique to make caustics appear in a typical swimming pool scene.

The idea behind the solution?
We will use two exact-copies water surfaces!

Original Surface Properties

This first surface will be set to cast no shadows (thus no real caustics). What this object needs to have, is a real water material that will be seen during rendering. Therefore, we will apply a water material using the Glossy layer (Image 2).

Copied Surface Properties

The copied surface should not be shown during rendering. We need to create a transparent material (Thin Film) with a caustics map in the Clipping panel. This way, the object will create “caustics” by casting shadows inside the pool.

What you will need to do…

  1. Duplicate the water surface object.
  2. Make the material of the copied object unique and use a Thin Film layer (Image 1).
  3. Turn off Visible in the properties of the copied model.
  4. Turn off Shadow Caster for the original model.

Water Material…

  • Glossy layer.
  • Blueish color at Transmittance.
  • A noisy texture on the bump map.

Thin Film Material…

  • Thin Film layer.
  • A caustics texture with a blue tone on the transmittance channel.
  • The same texture (grayscale) in Clip Mapping with Soft enabled. (Image 3)

Use the button below to download a simple scene using this technique.

Credits for the models used in the rendering: Ronen Bekerman & Evermotion

Image 1: Thin Film Material

Image 2: Water Material

Image 3: Clipping Map