Houdini Notebook #1: Vectors Along a Curve

Ever need a vector attribute that runs along a curve? Maybe you want to use it as a force for particle movement or FLIP fluids. Here are a few easy ways to do it.

One of the most underused and badly named SOPs in Houdini, the Polyframe SOP. If used on a curve, this will create a tangent attribute along the u coordinate. By default, this attribute is named tangentu, but you can just enter something more commonly used for effects, like N or v.


You can also use a Point SOP, go to the Force tab, and check on Add Edge Force. The vector point attribute created is called edge_dir. You can later remap this to N or v.

If you need to reverse the direction of the vectors, just use a Reverse SOP before doing these procedures.

Curly Maze

A maze like pattern made by copy stamping 3 different shapes onto a grid.

Grassy Grass

A grass simulation using fur. The movement is driven by animating the point normals on the surface using a Perlin noise offset. The color is changed by attribute transfer of point color from a single point in the center. No dynamics were used, only SOPs.

The style of the grass was inspired by a Playstation 3 game called Flower.

Umbrella Crowd

An animated walk cycle thats copy stamped on a simple particle system. Just having some fun.

SPH Geometry Melt

I used SPH fluid particles to drive the shape of the geometry to get a melting effect. The particle fluids have a high viscosity and surface tension.

High Viscosity and Surface Tension

The SPH particles are imported to SOPs and brought into a lattice that deforms the geometry. The rest input needs to be from the first frame.

Lattice SOP