Whitewater shading with Phoenix FD

By Hammer Chen

Whitewater is formed in a rapid, when a river's gradient increases enough to generate so much turbulence that air is entrained into the water body, that is, it forms a bubbly or aerated and unstable current; the frothy water appears white. --- Wikipedia
In this article, I am going to show you how to set up whitewater shading with Phoenix FD.

To set up a scene for whitewater shading you will need:

1. A Phoenix FD Liquid Simulator - for simulation of liquid and generate "Vorticity smooth" data
2. A Phoenix FD Fire/Smoke Simulator - this is not for simulation. This Fire/Smoke Simulator doesn't have to be high resolution, because it purely functions as a container to load up "Vorticity smooth" data from Liquid Simulator, and shading / rendering them as smoke.
3. LiquidSrc

Key steps:
1. Create a Liquid Simulator in the scene, just as regular liquid simulation setup, except you need to export Special Grid Channels called "Vorticity Smooth," this data will serve as a source of the whitewater. Run simulation.

2. Create a Fire / Smoke Simulator in the scene, be sure to align it with a liquid simulator. The two simulators don't have to be the same size or same resolution, but their default pivot position has to be perfectly aligned.

3. In the Input rollout of the Fire / Smoke Simulator, change the path from default to "$(same_as_output) PhoenixFDLiquid001". This specifies the source of "Vorticity Smooth" data that generate from step 1.

4. In the Rendering rollout of Fire / Smoke Simulator, check the Cutter Geom option, and select the PhoenixFDLiquid as you created in step 1. Click on Volumetric Options...

5. In the Volumetric Options of the Fire / Smoke Simulator, change the color of Constant Color to white color or any other color you like for "whitewater." In this case, I gave it a light blue color. Set the Simple Smoke Opacity to a higher value so you will have a more pronounced whitewater shading.

6. Now hit render, you should have something like the image above.

Left: without whitewater; Right: with whitewater

7. Final recap: whitewater shading setup allows you to render extra information from "Vorticity smooth" data as smoke that gives your liquid rendering more details in its shading. Enjoy~