Project 6

1
Project 6

• Tumbling Cube
• Fri, Nov 21, 2003
• Due Mon, Dec 8, 2003

2
Tumbling Cube

• Read the handout.
• Run Tumbling Cube.exe.

3
The Motion of the Cube

• The cube should move in a specified direction at
  a specified speed.
• It should also spin on a specified axis at a
  specified rotation rate.

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The Motion of the Cube

• You should create the following global variables.
• A point to store the cubes position.
• A vector to store the direction of motion.
• A vector to store the axis of rotation.
• A float to store the spin angle of about the axis
  of rotation.

5
Animation

• The animation will be handled in the idle()
  function.
• This is a callback function that is called
  whenever nothing else is happening.
• The prototype is
• void idle()

6
Animation

• The function clock() returns the number of
  milliseconds since the computer was last turned
  on.
• Use clock() to compute the elapsed time since the
  last call to idle().
• Then update the cubes position and spin angle.

7
Animation

• New position old position direction
  elapsed time.
• New angle old angle
• spin rate elapsed time.

8
Animation

• Then determine whether the cube bounced off any
  of the six faces of the frustum.
• If it did, then update the position of the cube.

9
The View Frustum

• The cube will bounce around inside the view
  frustum.

10
The View Frustum

• Use gluPerspective() to create the projection
  matrix for this frustum.
• You may use any angle, but I think a 90? angle
  will be easy to work with.
• This is the angle between the top and bottom
  faces of the frustum.
• The angle between the sides is determined by this
  angle and the aspect ratio.

11
The Top and Bottom Walls of the Frustum

• Assume the angle is 90?.
• What are the equations of the top and bottom
  walls?

12
The Left and Right Walls of the Frustum

• To find the side walls, we must take the aspect
  ratio into account.

13
Bouncing off the Walls

• The motion is in discrete jumps, so the cube will
  probably pass through the wall in one of its
  jumps.

14
Bouncing off the Walls

• When the center of the cube passes through a
  wall, we will relocate the center to the point
  where the cube would be if it bounced off the
  wall.

15
Bouncing off the Walls

• How do we calculate the new location of the cube?

(x1, y1)
(x2, y2)
(x0, y0)
x a
16
Bouncing off the Walls

• We will assume that the walls are parallel to the
  coordinate planes for the purpose of computing
  the reflected location, even though the wall is
  at an angle.

17
Bouncing off the Walls

• If we didnt do that, then the cube might get
  stuck in a corner.