Deborah R. Fowler
Introduction to
Python in Houdini
Posted on Oct 17 2018Updated on Feb 16 2020
- tips for Exercise 4
parsing your data files to get ready for Houdini (but not
using Houdini yet)
- building a snowman in Houdini
IF YOU WORK AT HOME BE SURE TO MATCH TO THE SAME VERSION WE ARE USING (see instructions here)
We are going to build the snowman by copying correctly sized spheres onto points. The steps are as follows:
- Create a geo node, dive inside (double click) and create a python node. (To create nodes use the tab menu)
- Start by creating a point
geo.createPoint()- This calls the function to create a point, but if you want to add properties or attributes to that point, you will need to use the value the function returns
point = geo.createPoint()
- Now you have a variable name that can be used to reference the point
- Next we want to create multiple points so we will create a loop. Houdini will store the information that we add each time.
- Take a look at the Geometry Spreadsheet - you will see the point numbers with their locations
- Next get rid of the "magic numbers" - add numpoints variable to control the number of points and then add an attribute called pscale
- The pscale value will be set in the loop so that the spheres
will scale to that size
- The position is set based on the radius and the starting
position of the sphere. The code below gives u s a stack of
equally sized sphere
Next add the line to manipulate the radius, baseRadius *= .8 and you have the code given below
Variations - rather than have the sphere centered on the origin, what if it were on the ground plane? How about parameters? How about making this a function?
A very common thing to do in Houdini is to set an object so that it stays on the ground plane. For example, the sphere below is on the grid by referencing the parameter rady and translating it up that value.
In this way, no matter what the size of the sphere, it will sit on the groundplane. So the expression in ty (Center's parameter) is set to ch("rady") which is the value of the radius in the y direction
This requires some changes to our code since the first sphere is already sitting on the grid, we do not need to move it. The next sphere will be the diameter of the previous spheres
Finally, user defined parameters are added so that we have a tool we could use to allow arbitrary amounts of snowballs and adjustable radius.
User defined parameter are added using the parameter dialog box and then are evaluated as seen below. Then the code is wrapped in a function and called.
