CPSC 424, Computer Graphics, Spring 2010
Lab 9: Walk Through

Your assignment this week is to create a maze and let the user walk through it (by pressing the arrow keys), as in the following applet. (Hit the "G" key to change between the global view of the maze and view of the "avatar" within the maze.)

The assignment is due on Wednesday of next week, April 7.

You can start with the file Maze.java, which already implements keyboard interaction but show only a blue rectangle on which you can build the maze. (Copies of this file and other files mentioned on this page can be found in /classes/s10/cs225/lab9.) If you have not already added the file SimpleAvatar.java to the glutil package, you will need to do so now.

To create the maze, you can use the MazeData class that is defined in MazeData.java. Create the data for a 51-by-51 maze using maze = new MazeData(51,51). The result is a 51-by-51 grid of cells where each cell is either open or is part of a wall. You can find out whether the cell at position (i,j) is open by calling maze.isOpen(i,j). All cells along the edges of the maze are walls; there is no exit from the maze.

You should create a 3D OpenGL realization of the maze by using a cube to fill each cell that is part of a wall. (Use the Cube class from the glutil package.) The cube should be 1 unit on a side, and the cube for grid position (i,j) should go at (i-25,0,j-25). This will center the maze at the origin, and it will lie on the blue plane that is already rendered in the Maze program. As soon as you create the maze, you can use the arrow keys to navigate through it (in the avatar view). However, you will be able to walk through walls -- and it probably won't look very good.

To complete the assignment, you have to do four things:

• The default viewpoint light is directional. This program looks better if a positional light is used instead. Make LIGHT0 into a positional light, at (0,0,0) in eye coordinates. [One line of code!]
• The cubes will look better if a texture is applied to them. You can use the brick image brick.jpg or some other texture image if you prefer. Everything that you need to know about textures is in Section 2.4.2. [Several lines in init() to load the texture and a couple lines in display() to enable and disable the texture.
• When in the global view, display a marker to indicate the current location of the viewer in the maze. In my program, I use a white peg for this purpose. [Several lines of code in display().]
• The user should not be able to walk through walls. You should restrict the user's motion to the corridors. In my version of the program, before moving the viewer I record the current position. If the move puts the viewer in an illegal position, then I restore the viewer to its position from before the move.

The last point, of course, the hard one. One surprise that I should have expected but didn't is that you can't even let the viewer get too close to a wall. The viewer has a "near clipping plane" that has to be at some non-zero distance in front of the viewer. If the viewer is within the near clipping distance of the wall, then the wall disappears from view, even though the viewer has not yet passed through the wall. In effect, you have to add a small buffer zone around each cube.

There are various approaches to this sort of "collision detection". The easiest, in this case, is probably just to go through all the cubes and test whether the viewer is too close to any one of them. Only the x and z coordinates are relevant.