Houdini Notebook #2: SOP Attributes to DOPs

You can easily use attributes that you created in SOPs in DOPs by using the point( ) or prim( ) expressions. In DOPs, the syntax is, for example:

point( $OBJID, 0, "Cd", 0)

Here I am grouping the pieces of the fractured object by primitive color:

Here I am using a Velocity Impulse Force DOP to give a sudden push in velocity at frame 30. In SOPs, I created a vector attribute called impulse.

If your attribute values change over time, you can check 'Use Deforming Geometry' in the DOP object nodes or use a SOP Solver to update the attributes every frame.

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.