Stanford CS348C-22W CG: Animation & Simulation, Prof.

Doug James

Homework #2: Procedural Modeling

Due: Wednesday, January 25, 2022 (midnight)

In this second assignment you will build on your initial experiences with Houdini in the first
homework to build and animate something more involved. See where your imagination takes
you. Submit an image or video of your result (as appropriate), and the result will be shown at
in-class Weeklies the day after the deadline (on Thursday).

For this second Houdini assignment you will click alone to further develop your skills. As in
all projects for this class, you are encouraged to read, watch and discuss material and ideas
with your fellow classmates. However, to get the full experience of modeling and animating with
Houdini, and get up to speed, you really need to use Houdini yourself to get the hang of it--plus,
it’s a lot of fun! Therefore your final submission should be based on your own work.

Resources for Learning Houdini

Revisit the many resources provided in the first homework for learning Houdini, and try watching
and exploring some more advanced tutorials related to topics of interest.
● Video Tutorials: Houdini is a highly visual node-based design tool, and so the best way
to learn how to use it is often to just watch videos of people using it. Fortunately there
are many very good instructional videos available online. Heads-up that 98% of the
material is too advanced initially, and/or you don’t need it for this class. I suggest using
the videos as resources to help you solve problems in your day-to-day modeling tasks.
● Houdini Documentation: These are super useful. You will have these documents open
most of the time you work in Houdini.
● Entagma: The Entagma tutorials cover more advanced topics, and can provide ideas on
how to tackle more advanced modeling problems later in the course.

Helpful Tips
Autosave is disabled by default: Again, remember to turn on autosave. Note that AFAIK it
needs to be turned on each time you make a new project--don’t forget. There are different
autosave settings you can adjust to make it work best for you, e.g., how often to save, how
many backups, etc.

Procedural Modeling
In this second assignment, you should explore more advanced procedural modeling in Houdini.
Again, there are no constraints on exactly what you should model--it’s up to you! Use this as an
opportunity to explore more advanced functionality, such as the following:
Stanford CS348C: Animation & Simulation Homework #2: Procedural Modeling

1. VEX code: Try writing VEX code to express geometric operations, e.g., using sin/cos, or
animations. Writing your own code is extremely powerful, and worth exploring.
2. VOP nodes: Alternatively, instead of writing VEX code directly, you can use the
VOP-based visual programming capabilities of Houdini (VEX Builder) for modeling
geometry, dynamics, shaders, etc. Some people prefer VEX or VOP, or you can use
both.
3. Implicit functions using OpenVDB are very expressive. Converting back and forth
between polygon and implicit representations provides a lot of flexibility.
4. Materials and rendering: Especially if you have prior graphics expertise, try exploring
the materials and rendering capabilities to make your results look better. Shader
networks (SHOPs) are very expressive.
5. Texturing: Houdini has a lot of texturing capabilities, which are especially useful for
building game assets.
6. Dynamics: A lot of functionality is simple to use, and ready “out of the box” using DOP
networks. For example, particle systems and rigid-body solvers are accessible. We will
explore these in future classes, so it is fine to ignore these for this assignment.
7. Solver SOPs are powerful ways to model things that depend on the previous frame,
e.g., growth processes. Check out CGWiki’s page on “The Solver SOP.” We will explore
this in later assignments, too.
8. Image compositing: You can use compositing node (COPs) networks to combine
images in sophisticated ways using COP networks. You could spend your whole
assignment exploring compositing operations inside a COP network.
9. Python interface: You may find it useful to control many aspects of Houdini from
python, especially if you are writing a “plugin” for some custom capability, or custom data
I/O.
10. Load in external datasets, and visualize them. Good examples include astronomy,
satellite and remote sensing data, machine learning, computer vision datasets, massive
point clouds, etc. Find ways to display the data in revealing and interesting ways.

Things to model and perhaps animate:

1. Re-make a famous visual effect.
2. Re-do your Homework #1 in an improved way.
3. Make a mini clip to reflect on an idea for your final project.
4. Model or animate a fractal growth process.
5. Model a building (windows, ledges, etc.) using repetitive structures.
6. Model a detailed moon covered in craters.
7. Render a shape using LEGO blocks.
Stanford CS348C: Animation & Simulation Homework #2: Procedural Modeling

8. Find a way to design mazes on images or surfaces

[Jie Xu and Craig S. Kaplan]

9. Design a still or animated logo for your club.
10. Design floral or another kind of ornamentation, e.g., on a birthday or holiday card for
someone special.

https://medium.com/@tokudu/computer-generated-floral-ornament-based-on-magnetic-curves-d77a3f206893

11. Visualize and/or animate a mathematical theorem, e.g., Gauss-Bonnet theorem.

12. Animate a volume integral, or a ray-triangle intersection test.
13. Make some mathematical art, e.g., using Fibonacci spirals.
14. Simulate Conway’s the “Game of Life”
15. Render a “pin board” animation using the ray node
16. Try modeling something you see around you. Usually that is a good source of
inspiration.

Submit your Work

There are two steps to submitting your work:
1. Weekly Artifact: Submit your image and/or short video artifact for the HW2 Weekly
using this Homework2-Artifact Dropbox file request link.
○ To make weekly video generation easier, we are restricting submission formats
this week. Please submit videos only, with the following restrictions:
i. 24 FPS
ii. 5 seconds long
iii. 1280x720 resolution--the maximum exportable from Houdini Apprentice.
iv. Acceptable formats:
● Quicktime mov format
● AVI format (if file size under 125 mb)
○ Tips on how to make a video
Stanford CS348C: Animation & Simulation Homework #2: Procedural Modeling

i. For mov and avi, create a Flipbook by clicking the flipbook icon on the
bottom left corner of the screen
ii. Go to the Size tab to ensure correct resolution, and edit the frame range
in the Output tab to ensure clip is 5 seconds long (the default frame rate
is 24 so this is 120 frames)
iii. Click Start. This opens up an MPlay window. Go to File > Export > … to
export the desired animation.
iv. For additional shading effects, the renderer can be used instead of the
flipbook (the button below Flipbook).
2. Canvas: Submit a zip file named to include with your first and last name (e.g.
‘doug_james.zip’) via Canvas that contains
● Your image and/or short video artifact, and
● Your Houdini *.hipnc file and any data files required to reproduce your result.
Please do not submit large amounts of metadata, simulation cache files, etc.
● A brief readme.txt file to point out any things we should notice.

Please acknowledge any sources that you based your work on, or inspired you, as well people
that may have contributed. Please do not use other Houdini assets, or others’ Houdini work, in
this assignment.

Grading Guidelines: We are flexible to accommodate a wide range of submission content, so

there is no hard rubric, however here are a few guidelines:
● Please submit the requested video format and Canvas zip by the deadline.
● Please include animation in your submission, not just a still image.
● Submit original creative content: Results generated using an existing tutorial, or a
standard shelf tool, without additional creative effort is discouraged.
● Reference all sources: please provide links to any tutorials or public asset files used

Re: Late submissions: Please submit what you can by the deadline. The course is on a tight
schedule, e.g., to participate in weeklies, and your participation is required in order for you and
others to get the greatest benefits. Part of hitting the deadline is scoping your project to not be
too ambitious. Start with a simple viable design, and improve it until you run out of time and
have to render & submit it.