VFX 721 / Spring 2026 / Fowler

Exercise 1 – Phyllotactic Pattern Demo

Date Assigned:	Class 2
Date Due:	Class 4 (NO RESUBMITS)

Checklist

☐ .hipnc
☐ .jpg beauty render (still)
☐ .mp4 animation

Goals

This assignment will focus on the student becoming familiar with Houdini and mastering the use of the copy methods (copy, copy to points, for-each), hscript (or VEX) expressions, and user-defined parameters. This will also be an exercise in following proper naming conventions for submission of exercises and projects. A rendered still and optional animation will acquaint the student with rendering in Houdini.

Requirements

Using the phyllotactic pattern formula discussed in class, create a visualization of the importance of the angle to the pattern.

Be able to adjust:
- the angle
- size of individual "florets"
- total number of "florets"
- the constant to spread the florets ("spacing" between them)
These adjustments should be accessible at the top-level node
A rendered still (.jpg) and animation (.mp4)

These are the minimum requirements.

Considerations

There is no resubmission for this exercise. Do your best – this is the first formal assignment your instructor will see from you. This is an exercise to get you prepared for Project 1.

Class Notes & Formulas

If you are having trouble remembering the formulas from class, here is the summary. See also the class notes or the Math for VSFX page on Phyllotaxis:

deborahrfowler.com/MathForVFX/Phyllotaxis.html

Given Vogel's formula for the spiral phyllotactic schematic:

r = c · sqrt( n )
θ = n × 137.508

Since for any given floret we know r (distance from center) and the angle, we can solve for x and y to plug into the position node's translate fields:

x = r · cos(θ)
y = r · sin(θ)

Substituting and using the copy number $CY:

x = c · sqrt( $CY ) · cos( $CY × angle )
y = c · sqrt( $CY ) · sin( $CY × angle )

Where c controls how spread out the florets are.

Starting out? You may begin with hard-coded values, e.g.:
2 * sqrt( $CY ) * cos( $CY * 137.508 )
Then add the parameter interface as you go. Once set up, use channel references:

ch( "../myParmName" ) * sqrt( $CY ) * cos( $CY * ch(
          "../angleName" ) )

Parameters are assumed to live in the top-level node.

Reminder: Turn translate cumulative off if using copy with stamp (deprecated – you are encouraged to use for-each instead).

Submission Guidelines

Submit a directory named:

S26_V721_E1_LastnameFirstname_Title/

This directory must contain:

S26_V721_E1_LastnameFirstname_Title/
├── S26_V721_E1_LastnameFirstname_Title.hipnc
├── S26_V721_E1_LastnameFirstname_Title.jpg
└── S26_V721_E1_LastnameFirstname_Title.mp4  (optional)

S26_V721_E1_LastnameFirstname_Title.hipnc
S26_V721_E1_LastnameFirstname_Title.jpg (or .png — no TIFs)
Note: always render to EXR; convert to JPG/PNG using mplay, Photoshop, or IrfanView.
S26_V721_E1_LastnameFirstname_Title.mp4 [optional but highly encouraged]
Compressed H.264 MP4 movie. Any file > 1 GB will not be accepted. Use Handbrake (free, Windows) with H264x codec.

No spaces in filenames! Adherence to naming and format conventions is required.
Failure to follow conventions will affect both your professionalism grade and your exercise grade.

Grading (out of 10)

Proper use of proceduralism and Houdini's node-based approach is the emphasis. Be creative and have fun!

What Professor Fowler is looking for:

Have you created a tool that can easily produce the pattern?
Does it have top-level parameters — specifically the four listed in the requirements?
Do you have default values that allow the user to revert to the pattern easily? Do things disappear?
Are you practicing good Houdini .hipnc habits?

Pushing further:

Have you created an animation?
Creativity and aesthetics count toward moving your grade to an A.

Minimum requirements met:	8 / 10
+ Properly submitted:	8.5 / 10
+ Creative (orientation, different/switching objects, color, animation):	9–10 / 10