HOU217 – Introduction to Houdini VEX and Python

CLASS 1: VEX BASICS, PART 1
In this class we go over the very basics of VEX by taking a look at its syntax as well as the concept of defining and declaring attributes, data types, and how to define vectors and access their components. We also cover the difference between VEX and Python when it comes to manipulating geometry and how its multithreaded design makes it so fast. Finally, we learn the difference between VExpressions and VEX code and how our Wrangles end up being converted.
CLASS 2: VEX BASICS, PART 2
Having learned the fundamentals in the previous class, we go over slightly more advanced concepts such as conditionals, functions, interface controls, local variables and reference variables. All these concepts will be applied in a simple dissolve effect, where we learn how to use the xyzdist and primuv functions as well as doing point cloud lookups in VEX. In the end, we have a short introduction to VExpressions in POP nodes and what are their differences.
CLASS 3: ADVANCED VEX
In this lesson we cover some more advanced VEX by looking at how to extract two non-collinear vectors out of any geometry using a for loop to create a transform matrix which we can re-apply to an animated object after fracturing it. Finally, we go over some useful VEX examples for Bullet, such as using deforming geometry and manually manipulating pieces.
CLASS 4: PYTHON BASICS
We switch from VEX to Python and have a look at Houdini’s Python API: the Houdini Object Model. To better understand it, we go over some Object Oriented Programming fundamentals and then explore how we can access objects from the hou module and how they relate to each other. We cover the Node, ObjNode, SopNode, Geometry, Point, Parm, Vector3 and Attrib classes and learn about the most common methods they have.
CLASS 5: PYTHON EXAMPLES
We apply all the knowledge from class 4 into two examples. In the first one, we go over how to load a CSV file containing every town and city in the United States along with their population, so we can create lights for each one of them and create a night time render of all the cities. For the last exercise, we create a useful tool to gather every Geometry ROP node in our scene and create a Fetch ROP for each one of them before finally merging them all together. We have a look at how to avoid having duplicate fetch nodes as well as allowing our system to be run at any time and only update the fetch ROPs with the newly created Geometry ROPs.

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