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3D Engine for Dummies
Author: KStor

Page 15
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The Rotations (con't)

Now we are going to do the buttons:

• open your first button (say the up-rotation around the x-axis). Enter this

  On (Roll Over)
   Set Variable: "sin" = -  basesin
   Set Variable: "cos" = basecos
   Set Variable: "axis" = "x"
  End On
  On (Release, Roll Out)
   Set Variable: "axis" = "none"
  End On

  The sign of the sine determines which direction the object turns. When you roll over the button, the axis turned around is set to x, and the sin and cos are stored. When you roll out, the axis is set to none. The principle is the same for all the other buttons, but with different values.
• x-axis down rotation

        Set Variable: "sin" =  basesin
   Set Variable: "cos" = basecos
   Set Variable: "axis" = "x"

• y-axis right-rotation

        Set Variable: "sin" = - basesin
   Set Variable: "cos" = basecos
   Set Variable: "axis" = "y"

• y-axis left-rotation

        Set Variable: "sin" = - basesin
   Set Variable: "cos" = basecos
   Set Variable: "axis" = "y"

• z-axis rotation(1)

        Set Variable: "sin" = - basesin
   Set Variable: "cos" = basecos
   Set Variable: "axis" = "z"

• z-axis rotation(2)

        Set Variable: "sin" = basesin
   Set Variable: "cos" = basecos
   Set Variable: "axis" = "z"

The last thing we have to do to make our rotation functional is obviously to program the rot frames. This is a simple use of the math-formulas. Open the rotx frame and enter this

Set Variable: "n" = "1"
Loop While (n<=totalpoints)
 Set Variable: "tmp" = (sin * eval("y"&n)) + ( cos * eval("z"&n))
 Set Variable: "y"&n = cos * eval("y"&n) - sin * eval("z"&n)
 Set Variable: "z"&n = tmp
 Set Variable: "n" = n + 1
End Loop

If you check this out it corresponds to the formulas in The Math. Now do the same for the roty frame:

Set Variable: "n" = "1"
Loop While (n<=totalpoints)
 Set Variable: "tmp" = - (sin * eval("x"&n)) + ( cos * eval("z"&n))
 Set Variable: "x"&n = cos * eval("x"&n) + sin * eval("z"&n)
 Set Variable: "z"&n = tmp
 Set Variable: "n" = n + 1
End Loop

and for the rotz frame:

Set Variable: "n" = "1"
Loop While (n<=totalpoints)
 Set Variable: "tmp" = (sin * eval("x"&n)) + ( cos * eval("y"&n))
 Set Variable: "x"&n = cos * eval("x"&n) - sin * eval("y"&n)
 Set Variable: "y"&n = tmp
 Set Variable: "n" = n + 1
End Loop

That's all, your engine is finished!

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Added: : 2000-12-04 Rating: 8.97 Votes: 2633 Hits: 4706

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KStor is a student living in France and working with Flash during his free time...that is, not very much.

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