Houdini FX Water FX: Realistic Trickling Rivulets & Wetness

Over the past few days, I completed an article titled “Houdini FLIP Surface Tension Demystified”, which includes a free HIP file with a full setup and has been warmly received by the Houdini community. It includes a free HIP file with a complete setup and clearly explained content. You can read it here: https://medium.com/@vupham_37726/houdini-flip-surface-tension-demystified-f1239da880ce

In the article, I also share a small technique for adapting surface tension into a more advanced with VEX code to fill the hole, easy‑to‑use, and robust method with strong art‑direction control. The content covers the complete workflow from simulation to meshing pipeline operations which is often a challenge for many Houdini artists.

While the article focuses heavily on how surface tension can help create tendrils and thin surfaces, it does not cover stringiness water, realistic droplets, trickling rivulets, and flowing rainwater. This additional technique, though a relatively small step, can significantly enhance realism by adding fine detail layers that complement the main animation, such as a character stepping out of water, soaking rain, sweating or rain dripping in dense drops.

The system is designed to work at any required scale, leveraging the FLIP solver without over‑reducing parameters, ensuring the generation of tiny droplets, dripping effects, and procedural rivulets. (How much more particle separation will you reduce to 64-bit float before waiting an eternity for the light to reach the universe's edge?)

This work was created with a simple setup for moving and interacting characters, simulating trickling rivulets for effects like stepping out of water or sweating—aimed at achieving the highest possible visual realism.

The setup also includes an improved wave curve approach for post‑processing, adding more detail to the water surface. This is an update from my previous setup, now presented with the full setup and final render. (my previous approach research • [Houdini] Attempt to Solve Wave Curve Post... )

The project was completed using Houdini FLIP, Solaris OpenUSD, Karma XPU, and compositing in NUKE. Each simulation took less than one minute, and the multi‑pass meshing operation took around 3–5 minutes.

Paper Wave Curve Approach: https://pub.ista.ac.at/group_wojtan/projects/2020_Skrivan_WaveCurves/wave_curves_2020.pdf
Inspired from Paper Residual wetness and rivulets from Weta FX on Pahi Water pipeline and toolset: https://alexey.stomakhin.com/research/pahi.html

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