15-462 Programming Assignment 4: Procedural Modeling

Due Thursday, Dec 6, 2007, 23:59:59

Updates

• Nov 26, 2007: Add Links section. Add more explanation on how to create a realistic cloud texture.

Description

For this project you will explore various techniques for procedural modeling and animation. The project will involve generating procedural textures, terrain, organic structures based on L-systems, and procedural animation of a flock of birds. Below are some screenshots of examples to give you an idea of the kinds of scenes you will be creating:
Simple planar fractal L-system tree.
 

More complex L-system tree with 3-D structure.

 

Required Features [100 points]

You must implement the following features:

• Fractal Terrain [25 points] - Create a terrain that is 100x100 units on the x and z axes. Note that this 100x100 units is not a strict requirement. Render whatever makes sense to you. The goal is to generate a height map based on perlin noise (you may utilize the example functions provided in the starter code file "noise.h". Note that the example functions are the implementation of smoothed noise, not Perlin noise. You need to compute Perlin noise yourselves based on that. Perlin noise is actually an aggregate of the smoothed noise function in some discrete frequencies. There are many ways to do aggregation. For example, you can make Perlin noise the weighted sum of noise function with respect to the frequency (i.e. Sum[1/f*noise], where f=1,2,4,...2^n.). In the 1-D case, Perlin(p) = 1/1*noise(1p) + 1/2*noise(2p) + 1/4*noise(4p) + 1/8*noise(8p) + ... . A few links on Perlin noise function is added to the Links section. ) After generating the geometry of the terrain procedurally, you should color or texture your terrain using a procedural technique. Also make sure you appropriate normals and lighting. Be sure to explain what you did in your "readme.txt" file.
• Procedural Cloud Textures [25 points] - Texture the skybox with procedurally-generated cloud textures. Think carefully about how you can avoid artifacts at the seams of the adjacent walls of the skybox. Your sky does not need to have lighting effects. Explain what you did in your "readme.txt" file. Your skybox does not need to be a cube like in the starter code. You can also look up how to create a realistic cloud texture in the link provided in the Links section.
• L-System Tree [30 points]
You are provided with an example parser for an L-system and are asked to fill in the rendering functions. Check out "lsystem.h" for additional information on the format and algorithm. The starter code comes with two sample files: "oaky.lsys" and "simple.lsys" (The two screenshots earlier on this page use them.)
It is recommended to use a simple stack-based system to recursively render trees with fractal-like structure. The starter code provides an almost complete implementation of this. However, feel free to implement an L-system renderer of your own design if you wish.
Once you implement the renderer, you will create your own cool looking tree file and submit it along with screenshots. (NOTE: please remember to "add" and "commit" all of the files you create to your subversion repository, and document them in your "readme.txt" file.
This score for this portion of the lab will be divided into two parts: your L-system renderer [20 points], and your custom tree file [10 points].
• ReadMe [5 points]
Include a readme.txt file using this template. Make sure to describe any extra features you implemented.
• Code Quality [10 points]
Use reasonably efficient and well-written code that can easily be graded.
• Representative Pictures or animation [5 points]
Save a number of still output pictures from your program to a directory labeled images, or output frames of an animation to a movie directory.

Extra Credit Features [maximum assignment score is 110 points]

• BOIDS Flocking [20 points] The term BOIDS usually refers to a simulation of a flock of flying objects. The original implementation of BOIDS had three steering behaviors: separation, alignment, and cohesion. These behaviors make sure that individuals stay with the group and move in a similar direction while maintaining a minimum distance between their neighbors.


Some things your implementation should consider:

• If a BOID goes outside of the boundary of the 100x100 grid, you may want to make the BOID "wraparound" to the other side.
• Avoiding collisions with objects in the world (such as trees) is extra credit. However, you should try to regulate a BOID's height above the terrain. One possible way to do this is to add penalty terms to the steering (heading direction) whenever a BOID's height becomes either too low or too high.
There is a "boid.obj" file in the starter pack which just contains, in text, a boid's positions and faces (starting vertex index is 1). You are welcome to reuse the parser from lab3, or create your own simple one (we won't be grading you on any other model file). Note that boid.obj doesn't have vertex normals, so you should reuse your code from lab1 to generate the normals. When moving boids around, their velocities should always be aligned with their forward direction (the "nose" of the boid).
• Animated cloud mapping [5 points] Instead of using 2-D Perlin noise for a still cloud mapping, use 3-D Perlin noise with the extra dimension for your time dimension.

Starter Code and Submission

You can find the lab 4 starter code here. To finish the required features, you should make changes to functions that have "FIXME" comments. There are 6 of them in total (4 in lsystem_render.cc and 2 in main.cxx). The submission guidelines remain the same as the previous labs. Please name your directory asst4_lsys. Make sure your project can be compiled by just going into the asst4_lsys directory and typing make.
 

Please include a copy of whatever models, textures, or additional data files you use when handing in your project as it makes life a lot easier to verify your features.