CMSC 435/634: Computer Graphics

Lab 4: L-systems in BMRT

Due November 1, 2000

Image by Przemek Prusinkiewicz

The Assignment

Your assignment is to adapt the L-system modeling program you implemented in Lab 3 generate true 3D plant models using BMRT. 3D L-systems are the most common techniques for creating trees and plants in computer generated images (as seen above). Your goal is to create plants which are as realistic as possible, so choose appropriate surface and lighting characteristics. You should use the same mechanism as before the create the string, but create a RIB output, along with the 2D display from Edge. In order to render your string in 3D, interpret the characters of the string as following:

• F
  Move forward a step of length d. Draw a 3D section of stem from the previous location to the new location.

  X

  Draw a leaf. Use a bicubic patch, NURB, or polygon(s) for each leaf. Pick an appropriate 3D orientation for each leaf.

  +

  Turn left by angle A. The positive orientation of angles is counter-clockwise.

  -

  Turn right by angle A.

The angle A is given as part of the grammar. You will want to add some rotation out of the plane of the stem, as well. One suggestion for this is to assume the plant uses spiral phyllotaxis and rotate the segments around the main stem by an appropriate amount. The twig length d should be initialized to a suitable value and decrease by 70% in each successive generation. You may also want to decrease twig diameter in successive generations. Your program should be able to handle at least 8 generations of a plant type.

At a minimum, your program should generate models for Plant1, Plant2, and Plant3 from Lab 3. You'll probably want to add another button to generate the RIB file from the plant model string.

Make your results as realistic as possible. Each of these should be added on additional buttons, so that Plant1 and Plant2 give the deterministic results described above.

Submit your assignment as 'lab4'. Your comments should include the environment (hardware and software) that you used to develop your program. To facilitate grading, your program should run properly on irix.gl, regardless of the system used for development. Include all necessary files and makefiles, as well as sample images from BMRT.