Project 3: L-systems

In this project I have used L-System nodes in Houdini to generate snowflakes and ice palace, inspired from Disney Frozen's Elsa's ice palace. This is my first project in Houdini.

Introduction to L-systems

An L-System is basically a complex recursive system which consists of:

An alphabet of symbols: our components (note that symbols can be abstract)
An axiom: initial configuration
A grammar: rules that determine what symbols appear in what contexts. Rules have

Preconditions
Postconditions

These symbols can be interpreted as rendering instructions. For example

F = draw a line, moving forward
- = rotate(30)
+ = rotate(-30)
[ = save position
] = store position

Houdini's L-System Nodes have many such useful symbols and values.

Snowflakes - 2D L-System

In this project I have used 2D L-systems to generate snowflakes using this tutorial.

First, I took a segment of a circle and mapped a 2D L-system on it. Using remeshing and color attribute, I procedurally created an L-System mesh to look like an icy, jittered, flat snowflake. Then I mirrored it around with rotation transformation to generate the entire snowflake. Then I randomized certain parameters liek number of generations and angles to generate random snowflakes.

Varying over time	Varying across instances

Rules

Axiom: X
X=F[+X][-X]FX
F=FF

Finally I scattered them across a grid using a noise function, randomized their orientation and added wind/drag nodes to generate snowfall.

Ice chandelier - 3D L-System

I used 3D L-system to generate ice chandeliers for my ice palace. It used additional houdini l-system symbols for rotating it about all 3 axes.

Skeleton	Mesh	Top-view

The chandelier 3 patterns, one at it's tip and two others constantly alternating with each chandelier layer.

Rules

Axiom: F|FFFX[&A][+B][^C][-D]FF
Rule 1: X=[&A][+B][^C][-D]/(45)[&A][+B][^C][-D]FH"Y
Rule 2: A=F[+"H][-"H]H[;(2)+H][;(2)-H]H[+H][-H]F
Rule 3: B=F[&"H][^"H]H[;(2)&H][;(2)^H]H[&H][^H]F
Rule 4: C=F[+"H][-"H]H[;(2)+H][;(2)-H]H[+H][-H]F
Rule 5: D=F[&"H][^"H]H[;(2)&H][;(2)^H]H[&H][^H]F
Rule 6: Y=[&P][+Q][^R][-S]/(45)[&P][+Q][^R][-S]FF"X
Rule 7: P=F[;;+"H][;;-"H][+"H][-"H]H[+H][-H]H[+F][-F]
Rule 8: Q=F[;;&"H][;;^"H][&H][^H]H[&H][^H]H[&F][^F]
Rule 9: R=F[;;+"H][;;-"H][+"H][-"H]H[+H][-H]H[+F][-F]
Rule 10: S=F[;;&"H][;;^"H][&H][^H]H[&H][^H]H[&F][^F]

All of it is parametrized and animated to grow with time variable.

More L-systems in the scene

Some other L-systems from the scene can be seen below:

Roof	Walls	Tip

Final scene

Inspiration/Reference	Houdini Render

rcj9719 / Procedural-Lsystems