Programming assignments #3 and #4 - 3D Video Game
CS 248 - Introduction to Computer Graphics
Autumn Quarter, 1999
Assignment #3 Demos on Monday, November 15
Assignment #4 Demos on Friday, December 3
Assignment #4 Writeup due on Tuesday, December 7 by 5:00pm
Your assignment is to write a 3D video game using OpenGL. You are free to
design and implement any sort of game you like, as long as it incorporates the
required functionality described below. For purposes of this project, we
consider a 3D video game to be an interactive 3D computer graphics application
which has a challenging goal, is fun to play, and incorporates some concept of
scoring or winning and losing. It is not required that your game idea be
original, but originality will be rewarded with extra credit. If you have any
questions about whether your idea meets the criteria for a 3D video game,
please ask the course professor or a TA.
You are permitted (and encouraged) to form teams of 2-3 people and partition
the work among the team members. The work expected from each team will be
proportional to the size of the team. You can use the class newsgroup
su.class.cs248 to find prospective team members.
Within the overall framework of your video game, you are required to include
the following functionality:
- 3D viewing and objects.
Your game environment must be a scene consisting primarily of 3D elements, as
opposed to only "flat," 2D sprite-based graphics. Your game should provide
perspective views of your 3D scene where at least sometimes the viewpoint
changes smoothly under some combination of user and program control. To
produce these views, you should implement transformation, clipping, and
hidden-surface removal of your 3D scene using the OpenGL pipeline.
- User input. Your game must allow players to interact with
the game via keyboard or mouse controls. Alternatively, you can use joysticks
or more elaborate user interface devices (provided that you can supply the
required devices for your program demonstration sessions; see below).
- Lighting and smooth shading.
Your game must contain at least some objects that are "lit" using OpenGL's
lighting model. For these objects, you'll need to define normal vectors and
materials, as well as create one or more light sources. See Chapter 5 of the
OpenGL Programming Guide for details on implementing lighting and
- Texture mapping.
You must implement texture mapping for at least one of the 3D objects in your
video game. In its most common form, texture mapping applies a detailed 2D
image or pattern to 3D geometric primitives. Texture mapping is used
extensively in modern 3D video games to improve graphic realism. Chapter 9 of
the OpenGL Programming Guide describes how to implement a variety of
texturing techniques. If you want, you can use your paint program from
Assignment #1 to create 2D texture maps in the .PPM image format, and
borrow part of the xsupport source code for loading image files in
In addition to these basic requirements, your game should incorporate some of
the more advanced computer graphics techniques listed below, depending on the
size of your project team. In particular, you are required to implement at
least 2*N of these additional techniques, where N is the
number of people on your team (i.e. groups of three people need to implement
six techniques, individuals working alone are required to implement only two,
etc.). Of course, you are encouraged to implement as many of these techniques
as you can, depending on the requirements of your particular game engine, as
well as using any other ideas you read about or invent on your own. Extra
effort will be rewarded with extra credit.
- On-screen control panel. Many 3D video games reserve
part of the display area for an on-screen control panel, which may include text
or 2D graphical elements for user controls, scoreboards, etc. Flight simulator
games often use 2D graphical overlays on the 3D world for "Heads Up Displays
(HUDs)." You can implement a control panel for your game using a variety of
techniques in OpenGL, such as orthographic projection and the stencil buffer.
Text primitives are not explicitly supported with OpenGL, but GLUT and the
window system extensions (GLX, WGL, etc.) both provide commands to help render
- Hierarchical Scene Graph. Many 3D graphics applications maintain
their constituent objects and sub-objects in a tree-like data structure called
a hierarchical scene graph. The scene graph provides a logical
organization for the objects in the 3D world, and allows for efficient
constructs and operations such as instancing, hierarchical transforms, nested
bounding volumes, and traversals of the scene graph for rendering or collision
detection. Object hierarchies are discussed in Chapter 7 of the textbook.
- View frustum culling. In video games with complex
3D environments, it is necessary to limit the number of 3D primitives drawn
each frame in order to maintain interactive rendering rates. One way to do
this is to avoid drawing any 3D objects which are outside of the viewing
frustum of the camera. You can pre-compute rough bounding volumes for
hierarchical objects or parts of your 3D world, and then test each bounding
volume to verify that some part of it intersects the view frustum before
drawing its contained objects each frame.
- Level of detail control. Another way to limit the number
of 3D primitives drawn each frame is to implement level of detail (LOD) control
in your game. One simple method of LOD control involves creating multiple
versions of some of your 3D objects, varying in geometric complexity (such as
10, 100, and 1000 polygons). Then, before drawing the objects each frame, you
can pick the most appropriate version of the object to render, depending on
such metrics as the distance of the object from the viewer, the complexity of
the current scene, or a user-selectable detail level.
- Occlusion culling. Yet another way to maintain good game
performance with complex environments is by performing occlusion culling.
Similar to view frustum culling, this technique involves using a conservative
computation to avoid drawing any parts of the 3D scene which won't be seen by
the viewer because they are hidden behind other objects. For static
environments such as buildings, you might pre-compute which regions of space
(such as rooms) are impossible to see from other regions (due to occluding
walls, for example). (Don't confuse occlusion culling with simple
hidden-surface removal, which is required for your video game.)
- Procedural and physically-based modeling. In addition to using
scanned or hand-modeled objects to populate the 3D worlds, some video games use
procedurally computed models. Chapter 20 of the textbook describes examples of
procedural modeling, including fractally-generated mountainous terrains and
L-grammars for generating models of plants. Procedurally generated textures
may be used to simulate effects such as fire, smoke, and clouds.
- Collision detection. Video games often contain moving objects
which trigger events when they collide, such as projectiles shot at a target.
Collision detection can also be used to prevent the user from passing through
walls or other objects. You can implement collision detection in a variety
of ways; the simplest might involve comparing bounding volumes of objects to
decide if they intersect or not. The Graphics Gems series of books
describes efficient intersection testing algorithms for a number of different
- Simulated dynamics. Your video game implementation might include
modeling dynamic behaviors and physics for objects in the 3D world. For
example, the wheels of a vehicle might react realistically as they move over
rough terrain, or a door might swing open differently depending on the force
exerted by the player.
- Multipass rendering effects. OpenGL makes it possible to
easily implement a wide variety of realistic rendering effects. Many
of these effects can be achieved by drawing the scene multiple times
for each frame, varying one or more parameters each pass through the
scene. Examples of such effects include soft shadows, full scene
antialiasing, motion blur, depth of field, bump-mapping, reflections,
refractions, and compositing. Good sources of information on
implementing these and other effects are in Chapters 10 and 14 of the
OpenGL Programming Guide, and in the OpenGL tutorials
available on the Web.
- Parametric curved surfaces. OpenGL can directly display only
simple convex polygons; however, you might create a 3D model for your video
game which includes smoothly curved surfaces represented mathematically by a
small number of parameters. Chapter 11 of the textbook and Chapter 12 of the
OpenGL Programming Guide describe how to represent and manage the
display of smooth surfaces such as NURBS. Be wary about performance if you use
NURBS in OpenGL; use them judiciously.
- Advanced image-based techniques. In an effort to increase
graphical realism and maintain fast performance, many video games mix
traditional 3D graphics rendering with 2D image-based graphics. Although 2D
texture mapping is an example of a basic image-based technique, more advanced
techniques such as environment mapping, billboarding, and projective textures
are possible. Other ideas for image-based techniques include precomputing
multiple 2D images ("sprites") of a object from different orientations, and
then choosing the most appropriate sprite to warp and render in the 3D scene.
See the pointers on the assignment Web page for examples and information on
implementing advanced image-based techniques.
- Sound. Adding appropriate audio effects to your game can provide a
more compelling experience for the player. The details of sound effect
creation and implementation of audio playback in your game engine will depend
on your hardware configuration; some pointers to relevant documentation and
sample sound effects are included on the assignment Web page.
- AI. Some video games include computer-controlled agents that
require a significant degree of artificial intelligence. Many of the
techniques taught in a basic AI course are applicable to video game
development, and some links to more detailed information on game AI are
included on the course Web page for the assignment. If you have any doubts
about whether a technique you are using qualifies as "AI" for this assignment,
- Networked multi-player capability. Networked multi-player video
games allow more than one player to play at once, either collaboratively or in
competition, using computer networks such as the Internet. If you add
multi-player capability to your video game, you'll need to deal with issues
such as network latency by using predictive techniques. Some pointers to basic
information on implementing networking in games will be provided on the
assignment Web page.
- Game level editor. Some video games are accompanied with
supplementary computer graphics applications which allow users to design their
own game levels (scenes). If you develop your own custom application to
construct levels while writing your game, you might consider packaging it as a
separate utility program for end-users to enjoy as well!
A few hints
- This project is purposefully designed to be more open-ended than
the first two assignments of the course. You will be expected to do a
considerable amount of learning on your own, particularly in gaining experience
with programming in OpenGL. In order to assist and inspire you, a web page is
available at the URL:
This page includes pointers to OpenGL tutorials, information on game
development, useful utility programs, and sources for 3D models and other game
content. Additional examples of OpenGL code from the programming guide and
OpenGL and GLUT distributions are available in the class directory in
/usr/class/cs248/assignment3. Of course, you are responsible for
understanding and implementing your own video game code; copying of source code
from others is prohibited.
Please take advantage of the opportunity to consult the course professor and
TAs with questions concerning development of your particular video game.
If there are computer graphics techniques not covered in the course that you
would like to implement, we will usually be able to point you to an
appropriate source of information.
- Interactive 3D graphics programs such as video games
place special demands on computer hardware. If your 3D world is particularly
large or complex, or if you use certain OpenGL rendering features (such as
texture mapping), you will probably need special graphics hardware in order to
get real-time performance. Note that the SGI machines in Sweet Hall do not
implement texture mapping in graphics hardware, so games making intensive use
of texturing will suffer performance limitations on these systems. Modern PC
systems with fast 3D graphics accelerator cards will usually yield better
texturing performance than the SGI machines in Sweet Hall. If you develop your
game on multiple platforms, it will probably be useful to add options to
disable expensive features (such as texturing) on request. The performance of
your video game is important, so do not implement too many expensive rendering
features if the gameplay is negatively impacted! There are some pointers on
the assignment Web page to sources of information on maximizing OpenGL
- Most successful video games include richly detailed 3D models, textures,
sounds, and other content for representing the game world and characters. You
have several options available in creating the 3D models for your video game:
- Simple models can be sketched on graph paper, and the coordinates
manually typed into your source code.
- Models can be procedurally generated, as mentioned above.
- You can use a 3D modeling package and export the model in
a format your program can read.
The assignment Web page will contain pointers to several freely
available modeling packages.
- The GLUT library provides functions for drawing a few simple
3D shapes (sphere, cube, teapot, etc.)
- You can find a wide variety of 3D models available on the Web
(see the pointers on the assignment Web page). These may need to be
converted to a format your program can use.
- You are free to develop your video game on any computer platform that
supports OpenGL, provided that you will be able to demonstrate your program at
the two required demonstration periods at Sweet Hall. If your program cannot
run on the Sweet Hall SGI machines, you will be responsible for bringing a
system on which to run your video game. We are currently investigating the
possibility of making a PC running Windows with a 3D graphics accelerator and
sound card available for testing and demos in Sweet Hall, but we cannot yet
make any guarantees. Even if we do succeed in installing a PC, demand will
be high, so you should be prepared to bring your own, or collaborate with
other groups in different demo time slots to bring a PC. Versions of OpenGL
for most common computing platforms are available for download at
sites pointed at from the assignment Web page.
To keep things simple, our recommendation is to develop your video game on the
Sweet Hall SGI systems. OpenGL is window system independent, so an additional
toolkit is necessary to provide the necessary windowing and input event
management; for this we recommend using the GLUT package. GLUT is used for all
the examples in recent editions of the OpenGL Programming Guide, and
is available for most all common computing platforms. An example program and
Makefile using OpenGL and GLUT on the Sweet Hall SGI machines is available in
GLUT offers a very limited set of user interface widgets (little more than
menus). If you require more extensive user interface functionality, we
recommend the MUI toolkit; it is very easy to use, and is written entirely on
top of GLUT and OpenGL. The MUI libraries are available in the class
directory, and documentation for MUI is available on the Web (see the
assignment Web page for the pointer). You are free to use other user interface
toolkits of your choice.
- In the course of designing and implementing your video game,
keep in mind that CS248 is a computer graphics course. Focus your efforts on
the computer graphics techniques underlying the game; don't spend the majority
of your time on game design or object modeling if the graphics engine will
suffer as a result!
Video game submission requirements
Assignment #3 will serve as a checkpoint on the progress of your video game.
On Monday, November 15 you will demonstrate your program to a member of the
CS248 course staff. No writeup or submission of source code or other files is
required for this phase of the project. To show reasonable progress, your
"gameplay" should be basically working, and most of the required graphics
functionality (3D viewing, user input, lighting, and texture mapping) should be
implemented. The 2*N "advanced" techniques need not be in place. At
the demo, we will give you feedback about your game, and we will discuss with
you your plans for assignment #4. However, your grade for assignment #3 will
be based only on the functionality you demonstrate on November 15.
Your final video game (assignment #4) will be demonstrated on Friday, Dec. 3.
In addition to the CS248 course staff, a jury of computer graphics experts from
industry and academia will be on hand to evaluate your programs as part of a
video game competition. There will be one grand prize - an
all-expenses-paid trip to Siggraph 2000
in New Orleans next summer, one second-place prize -
dinner for two at Il Fornaio
in Palo Alto and a copy of the
Siggraph '99 Electronic Theater videotape,
and three third-place prizes - a copy of the
Siggraph '99 Electronic Theater videotape.
If the grand prize is won by a team, it must be split among the team members.
All other prizes will be duplicated as necessary to cover the team.
Final writeups and code and content submission for assignment #4 will be due on
Tuesday, Dec. 7 at 5:00pm. At that time you should include a README file which
describes how to build and run your video game, as well as explaining the
computer graphics techniques you used. Also, your README file should include
references to any external sources you referred to for inspiration, and should
indicate how your 3D models and other game content were obtained. To submit
your video game files, simply change the current directory to your assignment
#4 directory and run the submit script, as you did for the first two
assignments. Remember - no late demonstrations or writeup submissions will be
accepted for assignment #4.
Good luck, and have fun!
November 17, 1999 05:15:09 AM