Kevin,
Use x and y as they are. Decide how big your ball is when it is as close as possible to the user iDiaNear. Then decide how big the ball is when it is farthest away iDiaFar. Use Z as a multiplier for the ball diameter...

eg if;
max value for your Z is 480 [zmax]. ' Max room depth
iDiaFar is 22. ' Diameter of the ball at the farthest point
iDiaNear is 64. ' Diameter of the ball at the Nearest point
Z = 240 then ' Current Z of th ball
iBallDia = 38 ' Current diameter of the ball

iBallDia = (iDiaNear - (iDiaFar*2+1)) / (z/zmax) ' Your diameter formula
' ** iDiaFar*2+1 allows for a size freedom.

The meat of this is to ignore z regarding placement. Z only regards perception. Use the formula above and you are all set. This all assumes your user cannot enter the room. If he can you need to figure his Z and subtract it from Z so perceptions are maintained. ;}

Lastly, DirectX will handle this for you quite well, I tech edited DirectX 8 and Visual Basic Developement by Keith Sink. SAMS publishing 0-672-32225-0

HTH,
Joe

>Hello everyone!
>
>I am wrestling with a problem that I was wondering if anyone might have an answer to...
>
>I am trying to write a formula for a ball bouncing in a room.
>
>The values I feel necessary are...
>
>Ball_X, Ball_Y, Ball_Z (current location of ball in 3Dimensional room.)
>Screen_ball_X, Screen_ball_Y (actual location of ball on screen)
>
>Assuming room is 20 ft high, 20 ft wide, and 40 feet long (or perhaps better to say 240 by 240 by 480 inches) how would I transpose this three dimensional model into a two dimensional visual representation on the screen.
>
>I also recognize I need variables such as gravity, resistance (eg. ball rolling on floor), velocity and direction but right now I am just trying to figure out a simple formula for translating 3D ballX, BallY, and BallZ to 2D BallX and BallY.
>
>Any thoughts would be greatly appreciated!
>
>Thanks!