Customize caustics in the water system

A swimming pool with water caustics below the surface.

Customize the appearance of caustics, which are bright light patterns on GameObjects caused by the curved water surface reflecting and refracting light.

Create caustics from larger waves

By default, the High Definition Render Pipeline (HDRP) uses the ripples simulation band to calculate caustics.

To calculate caustics from larger waves in a river, ocean, sea, or lake, follow these steps:

  1. Select the water surface GameObject.
  2. In the Inspector window, go to Appearance. In the Caustics section, set the Simulation Band to a different band.
  3. Increase Virtual Plane Distance until you get the desired result.

To prevent aliasing artifacts, set Caustics Resolution to a higher value.

On the left, caustics with the simulation band set to Ripples. On the right, caustics with the simulation band set to Swell First Band.
On the left, caustics with the simulation band set to Ripples. On the right, caustics with the simulation band set to Swell First Band.

Add caustics above water

To add caustics to GameObjects above water, for example the parts of a boat that sit above the water surface, follow these steps:

  1. Create a Decal Projector.
  2. Add a script to the Decal Projector that uses the GetCausticsBuffer API to get the caustics texture from the water surface, and apply the texture as the Decal Projector texture.

For example:

using UnityEngine;
using UnityEngine.Rendering.HighDefinition;

public class ProjectCaustics : MonoBehaviour
{
    public WaterSurface waterSurface;

    void Update()
    {
        this.GetComponent<DecalProjector>().material.SetTexture("_Base_Color", waterSurface.GetCausticsBuffer(out float regionSize));
    }
}

Caustics have the following limitations with transparent GameObjects:

  • When the camera is above a water surface, HDRP calculates caustics using the position of any opaque GameObject behind a transparent GameObject.
  • HDRP doesn't apply caustics to transparent GameObjects when the camera is underwater.
  • Caustics don't react to current maps and water masks.

Make caustics less visible

You can reduce the absorption distance of the water surface. When water has a lower absorption distance, it's muddier and refracts less light, which makes caustics less visible.

To make caustics less visible, follow these steps:

  1. Select the water surface GameObject.
  2. In the Inspector window, in the Refraction section, decrease Absorption Distance.

Additional resources