Building and animating an interactive world in three or four weeks requires close planning and teamwork. Here are some guidelines to help with planning.

Agree on a storyboard for the project. Each team-member must buy in to the same concept otherwise the pieces will never fit together.

Your virtual world will be more engaging if you are clear about its goals and you are able to communicate those goals to the user. Goals may be communicated:

• Explicitly, by written or spoken instructions.
• Visually, by presenting interesting or obvious targets, or by using signs or other visual icons.
• Implicitly, by virtue of things "happening" as you approach or touch an object.

Storytelling is an art. I suggest you do some reading on it. Randy Pausch's SIGGRAPH '96 article about the Disney Aladdin VR ride is a good source for a start. Be creative; look into folklore, fairy tales, children's stories, and of course games to see how they tell their story and engage you, the user, to read or explore further.

An interactive storyboard is a collection of sketches or drawings showing the approximate "look and feel" of the world. The interaction arises as alternative paths through the storyboard. These paths are triggered by interactive events and can have several forms:

• View changes do not affect the action, but allow exploration of the 3D world. It is useful to restrict exploration, but it is a bit harder to implement. For example, one can use collision detection to avoid passing through walls or the ground plane. Another approach is simply to map inputs to a limited set of movements; e.g., a character is always moving on the ground plane even if that plane changes elevation.
  
  View changes will not generally affect the flow of your storyboards, though they will possibly appear as a set of alternatives (in parallel) at any state.
  
  
• User actions precipitate object responses. Thus moving near an object may cause it to change state or execute an animation; looking at an object may do similar things. Launching a projectile may involve computing a trajectory and doing an intersection test.
  
  These actions will appear as choice points with alternative storylines in your storyboards. The storyboard will become a tree with these user choices.
  
  
• Time may precipitate object responses. Object states may change on their own if nothing else happens (a clock is ticking, water is running, food is rotting, etc.)
  
  You might show a selection of object states. These changes may be drawn along parallel timelines for the objects in the world.
  

Until we get you some real interactive VR devices, the mouse and keyboard will have to serve as your input devices. Write your code so that these devices may be easily replaced by better input devices as they become available. For example, write a procedure to input direction information; it can be bound to the keyboard or the Flock of Birds without changing your application code.

Design top-down! There isn't much time to create an interactive virtual world. If you get hung up in the details the overall flow may not happen. Model with simple shapes then elaborate as time permits. Do sliding before walking. Do static faces before adding moving eyes and expressions. Design for several interactive options but get the basic ones working first; expand the range of choices if you have time.