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• Andy Nicholas

# Houdini Cheat Sheet

Updated: Jan 20, 2021

At popular request, this cheat sheet for Houdini has been brought over from the old website. Originally written for Houdini 10.0(!) it's still just as relevant now, and maybe even more so since there are so many extra nodes and features available.

It’s probably got about 95% of what you need to use when you first start out using Houdini.

Hope you find it useful.

### Commonly Used SOP Nodes

I feel that the Point Wrangle SOP deserves an honourable mention as one of the most powerful and versatile nodes. It's not included above as it's not something I would recommend for a beginner to jump into straight away until the basics are understood.

However, once you're comfortable with VEX you can end up replacing large portions of your node graphs with Point Wrangle SOPs. It lets you do a lot in a single optimised node, and allows you to perform complex logic in a readable way.

As always, it's a balance. Implementing everything in VEX can make your scenes impossible to understand for those not familiar with it.

### Commonly Used Expressions

You can find the full list of Houdini expressions here: https://www.sidefx.com/docs/houdini/expressions/index.html

Houdini expressions also contain the common mathematical functions that are found in most scripting and expression languages. Here are just a few:

`sin, cos, tan, asin, acos, atan, atan2, abs, pow, sqrt, ceil, floor, atof, dot, cross, deg, rad, exp, frac, hsv, rgb, min, max, log, log10, round, substr, strreplace`

Note: Trigonometric functions accept angles in degrees.

The modulus operation is achieved using the % character, and boolean logic is achieved using the standard C operators, i.e.

` <    >    <=    >=    ==    !=    !    &&     ||`

### Commonly Used Local Variables

The following variables are NOT available in every operator. Each operator has its own local variables, and you can find which ones in Houdini’s help documentation. The ones listed here are the ones you’ll most commonly encounter.