3D Engine for Dummies - Page 11

The Routine (con't)

The drawing routine
This is the very core of the engine: the program that converts the 3D coordinates to 2D coordinates (as explained in The Math). In the fifth frame, draw, enter this:

• Set Variable: "normalz" = depth * depth

  Normalz is the value k in the plane equation, depth being the z-coordinate of the normal vector of the view-plane (the plane being parallel to the xy plane, the vectors coordinates are (0,0,depth))

• Set Variable: "n" = "1"
  Loop While (n<=totalpoints)
        Set Variable: "u" = (depth - eyez)/(eval("z"&n) - eyez)
        If (n<=9)
              Set Variable: "2Dx0"&n =  u * eval("x"&n) + centerx
              Set Variable: "2Dy0"&n =  u * eval("y"&n) + centery 
        Else
              Set Variable: "2Dx"&n =  u * eval("x"&n) + centerx
              Set Variable: "2Dy"&n =  u * eval("y"&n) + centery 
        End If
        Set Variable: "n" = n + 1
  End Loop

  This part is a bit more complicated. We actually convert the 3D coordinates to 2D coordinates. For each point, we first calculate the value u as explained in The Math. Then we recalculate the 2D coordinates by multiplying the 3d coordinates by u. I can't explain exactly what I've done here but if you study the math link I gave you should be able to understand it.

• Set Variable: "n" = "1"
  Loop While (n<=totallines)
        Duplicate Movie Clip ("/baseline", "line" & n, n)
        Call ("drawline")
        Set Variable: "n" = n + 1
  End Loop

  Finally we just draw the the lines by duplicating the basic movie clip and calling the drawline frame.