Programming assignment #1 - Basic ray tracer
CS 348B - Computer Graphics: Image Synthesis Techniques
Spring Quarter, 1999
Due Wednesday, April 21, 11:59pm
The project for this quarter is to write a ray tracer. In assignment
#1, you will assemble the basic building blocks for recursively tracing
rays through scenes composed of triangles and spheres. A secondary goal
of this assignment is to familiarize you with the SGI graphics workstations
and the software tools that you will use during the remainder of the quarter.
The front end
The front end for your ray tracer will consist of i3Dm, a modeling program
written by Silicon Graphics, and Composer, a scene manipulation package
based on Inventor, Silicon Graphics's 3D graphics toolkit. i3Dm allows
you to interactively define simple 3D models. Composer allows you to interactively
assemble scenes composed of boxes (constructed from triangles), spheres,
and models imported from i3Dm (which Composer converts into triangles).
Composer also allows you to select viewing parameters, define directional
or point light sources, and specify reflectance properties for each object
in the scene. For scenes of modest complexity, Composer provides real-time
shaded renderings as feedback.
Your renderer will be a standalone C (or C++, if you prefer) program that
runs alongside Composer. Using our X support package, you will construct
a menu containing a display window and any number of Motif sliders and
buttons. The latter allow you to interactively control rendering parameters
not supported by Composer, of which you may have many by the end of the
quarter. Your menu should include buttons for retrieving the current scene
geometry, shading, and viewing parameters from Composer and for saving
the rendered image in a file. We provide the routines for performing the
actual file I/O. You should also provide a slider for controlling image
size. Finally, you should provide a "Render" button. When hit, you will
render the scene using your ray tracer and display the resulting image
in the display window. Don't expect your ray tracer to run in real time.
Read a scene description describing the camera, lights and a set of objects
with associated material properties from a file created by Composer.
Cast rays into the scene to simulate the image formed by a pin-hole camera.
One ray per pixel is sufficient for now.
Intersect rays with the geometric primitives. Don't worry about speed yet.
Implement Whitted's illumination model (Foley, van Dam, Feiner, and Hughes,
Computer Graphics: Principles and Practice, eq. 16.55), which
includes ambient, diffuse, and specular terms for each light source as
well as reflection and refraction terms. You only need to handle directional
and point light sources, i.e. no area lights, but you should be able to
handle multiple lights.
Write an image file containing your synthetic image.
Writing a ray tracer
Paul Heckbert's chapter in Andrew Glassner's
An Introduction to Ray
Tracing gives a good overview of how to write a ray tracer. Feel free
to copy his organization and examples. Using his nomenclature, Composer
SceneRead routine and defines your
data structures. You must write the
Shade routines. If you're having trouble converting pixel positions
into ray directions, see Glassner's A Simple Viewing Geometry in
Gems II (HO #7). To render triangles and spheres, you will need
two intersection routines. See sections 2 and 3 of Haine's chapter or section
15.10.1 of Foley, van Dam, et al. Also feel free to use Heckbert's ray-sphere
intersection code (in Glassner).
The support software you need for this project is contained in /usr/class/cs348b.
Look at the README file and the software and other README files that it
references. Although xsupport/scene_io.h talks about ellipsoids, per-vertex
materials, and meshes, you can ignore all of these. You only need to handle
spheres and triangles, and you can assume one material per object. In programming
assignment #3, you are welcome to add these other features.
Design your software to be modular so that you can extend it. In programming
assignment #2, you will add an acceleration scheme. In programming assignment
#3, you will add one or more extensions of your own choosing.
Notes on Whitted's illumination model
The first three terms in Whitted's model will require you to trace rays
towards each light, and the last two will require you to recursively trace
reflected and refracted rays. When tracing rays toward lights, you should
look for intersections with objects, thereby rendering shadows. If you
intersect a semi-transparent object, you should attenuate the light, thereby
rendering partial shadows, but you may ignore refraction.
Note that the light strengths and attenuation factors you get from Composer
are not appropriate for ray tracing. Moreover, you are not building a radiometrically
correct ray tracer. To facilitate debugging and grading, use the mapping
from Composer's material attributes to the terms in Whitted's illumination
model that is suggested in README.composer, scaling these attributes if
necessary to make your images look roughly like the samples (see below).
Your ray tracer should be able to handle the three test scenes test1.out,
test2.out, and test3.out in the directory /usr/class/cs348b/proj1/tests.
If you want to look at these scenes in Composer, load the corresponding
.iv files. Also included in that directory are sample images produced by
a ray tracer from last years' class. You should run your ray tracer on
those scenes and save the images it produces. In addition, you should create
two more scenes of limited complexity to test your system. Save those scenes
and the images produced. The majority of your grade will be based on your
results, although we will look briefly at your code to make sure it is
When you have completed your assignment, make a copy of your code and
the test scenes and associated images in a directory called project1 in
your home directory. Write a README file with enough information so that
we know what is there. Then follow the instructions in /usr/class/cs348b/README.submit
to complete your submission. Don't touch the files in that directory after
the due date.
Copyright © 1998 Marc Levoy
Last update: Wednesday, 07-Apr-1999
modified by firstname.lastname@example.org