Time Driver SOP

I have recently uploaded a useful digital asset to the Houdini Exchange. It is the Time Driver SOP. It is a useful node that lets you re-time animations, particle animations, particle fluid sims, etc. to your liking. It uses a combination of the Warp CHOP, Time Blend SOP, and the Time Shift SOP.

The Time Curve parameter is the time ratio that the animation will run. So a value of 1 is normal, 0.5 is half speed, and 2 is twice the speed, etc. You can keyframe this value as well, so you can have a fluid sim that slows down abruptly at a specific frame or gradually changes speed. Negative values will run it in reverse.

Example of the time curve. The animation will go in slow-motion
at frame 50 and then return to normal at frame 100.

You can also use a .clip or .bclip file you have exported from CHOPs or another software. Just check on the toggle.

Warning: If you merge two or more particle systems before using this node, the particles will not act as expected because the particles have overlapping IDs. So only use one particle system at a time.

It is also recommended to use .bgeo file sequences to be safe.

I used this node alot in production and it saved me loads of time in that I didn't have to try to match the timing of particles in the simulation. Instead, I just used the animations with no time warps, exported the time curve as a .clip file and used the node at the end. I was also able to tweak the timing of any particles or simulations in a flash!

You can find it in the Side Effects website's Houdini Exchange or just click Here!

Hope you find it useful.

Platonic Solids and Duality

I recently came across a post on odForce about hexagonal meshes. After searching info on this subject, I came across the concept of polyhedrons. This stuff is pretty interesting. Polyhedron in Greek means "many faces", so its just a 3-dimensional shape with many faces. There are special polyhedrons called Platonic Solids.


The image above are the 5 Platonic Solids and their "duals". Only 5 of them exist. All angles in these special polyhedrons have equal faces, angles, and edge lengths.
The dual is when you change each vertex to a face. And when this happens on a platonic solid, the number of points and primitives gets swapped.

In Houdini, just use a Platonic Solids SOP to get them.


The last two types, Soccer Ball and Utah Teapot, are technically not platonic, but they have been used so much in computer graphics, that they have become adopted!

To get the dual, use a Divide SOP with "Convex Polygons" unchecked and "Compute Dual" checked.

If you go to Wikipedia, and search polyhedron or platonic solids, you can get alot deeper than this.

Anyway, to the hexagonal mesh thing, here is a way to do it. Take a grid, then use a PolyBevel SOP with "Relative Inset" set to 1, then the Divide SOP with Compute Dual and keep Convex Polygons checked.

You end up with a nice honeycomb shape! You can then go further and use PolyWire, PolyExtrude, etc. and do some neat things with it.