Using Advanced Physics Concepts - Learn Unity3D Programming with UnityScript - page 189

if the boolean movingBack is true, then the normalized fractional amount delta is subtracted from
step , otherwise
(8) else step += delta;
the normalized fractional amount delta is added to step .
(9) step = Mathf.Clamp01(step);
Mathf.Clamp01 is a function that “clamps” a value between 0 and 1 and returns a float value. In this
case, if step -=delta ever drops below 0, Mathf.Clamp01 would simply return 0. If step += delta is
greater than 1, Mathf.Clamp01 would simply return 1. For any value between 0 and 1, Mathf.Clamp01
returns the same value.
(10) rigidbody.MovePosition(Vector3.Lerp(platformStartPosition,
platformEndPosition, step));
Instead of moving the platform game object by setting its Transform position, Rigidbody.MovePosition
tells the physics engine to move the game object to the new position. By using the physics engine,
any other objects will be pushed aside according to their physical properties, maintaining consistent
behavior as this game object is moved. Using Vector3.Lerp smooths the movement of the game
object.
(11) if(step == 1.0f) movingBack = true;
Recall that if movingBack is false , the value of step is increased by the value of delta , then in
(9) step = Mathf.Clamp01(step) returns 1 if the value of step is equal or greater than 1. When step
reaches the value of 1, movingBack is reassigned as true , so when the next fixedUpdate() call
reaches (7) the platform will begin to move in the opposite direction.
(12) else if(step == 0.0f) movingBack = false;
This is the reverse of (11). When step is decremented to 0 the boolean value of movingBack is
reassigned to false , so when the next fixedUpdate() call reaches (8) the platform will reverse
direction again. Save the script, attach it to the Platform 4 × 1× 4 game object, and Play. Try
changing duration and lowLevel until you feel it is a sufficiently challenging obstacle. Save the
scene and save the project (Figure 7-3 ).