How to AddForce OverTime?

Question

Hi there, I wanted to add into a FPS the ability to use lift like found in Bungie's game Destiny, I was able to get a second jump to occur after leaving the ground but I can't get it to sustain the added force for a given time. Here's my code:

 //Walking variables
 var walkAcceleration : float = 5;
 var walkDeacceleration : float = 5;
 var walkAccelAirRatio : float = 0.3;
 @HideInInspector
 var walkDeaccelerationVolX : float;
 @HideInInspector
 var walkDeaccelerationVolZ : float;
 var cameraObject : GameObject;
 var maxWalkSpeed : float = 20;
 @HideInInspector
 var horizontalMovement : Vector2;
 
 //Jumping variables
 var jumpVelocity : float = 40;
 @HideInInspector
 var grounded : boolean = false;
 var maxSlope : float = 60;
 
 //Lift variables
 var liftVelocity : float = 20;
 var liftDuration : float = 3;
 var liftCDTime : float = 5;
 var usingLift : boolean = false;
 
 function Start () 
 {
 
 }
 
 function Update () 
 {
     horizontalMovement = Vector2(rigidbody.velocity.x, rigidbody.velocity.z);
     if(horizontalMovement.magnitude > maxWalkSpeed)
     {
         horizontalMovement.Normalize();
         horizontalMovement *= maxWalkSpeed;
     }
     rigidbody.velocity.x = horizontalMovement.x;
     rigidbody.velocity.z = horizontalMovement.y;
     
     if(grounded)
     {
         rigidbody.velocity.x = Mathf.SmoothDamp(rigidbody.velocity.x, 0, walkDeaccelerationVolX, walkDeacceleration);
         rigidbody.velocity.z = Mathf.SmoothDamp(rigidbody.velocity.z, 0, walkDeaccelerationVolZ, walkDeacceleration);
         liftDuration = 3;
         usingLift = false;
     }
 
     transform.rotation = Quaternion.Euler(0, cameraObject.GetComponent(MouseLookScript).currentYRotation, 0);
     
     if(grounded)
     rigidbody.AddRelativeForce(Input.GetAxis("Horizontal") * walkAcceleration * Time.deltaTime, 0, Input.GetAxis("Vertical") * walkAcceleration * Time.deltaTime);
     else
     rigidbody.AddRelativeForce(Input.GetAxis("Horizontal") * walkAcceleration * walkAccelAirRatio * Time.deltaTime, 0, Input.GetAxis("Vertical") * walkAcceleration * walkAccelAirRatio * Time.deltaTime);
     
     if(Input.GetButtonDown("Jump") && grounded)
         rigidbody.AddForce(0, jumpVelocity, 0);
 
     if(Input.GetButtonDown("Jump") && !grounded)
         {
         usingLift = true;
             if(liftDuration > 0)
                 {
                     rigidbody.AddForce(0, liftVelocity * liftDuration, 0);
                 }
         }
     
     if(usingLift)
     liftDuration -= Time.deltaTime;
 }
 
 function OnCollisionStay (collision : Collision)
 {
     for (var contact : ContactPoint in collision.contacts)
     {
         if(Vector3.Angle(contact.normal, Vector3.up) < maxSlope)
         {
             grounded = true;
         }
     }
 }
 
 function OnCollisionExit ()
 {
     grounded = false;
 }

It counts down the liftDuration variable properly but aside from the initial force exerted when pressing the jump key it isn't sustained so I can't make it seem like you are hovering using a thruster or jump pack. Any ideas on how I can fix this?

Answer 1

Best Answer

Answer by dmg0600 · Sep 19, 2014 at 05:13 PM

The problem is you are using Input.GetButtonDown("Jump") for the lift effect instead of Input.GetButton("Jump").

Input.GetButtonDown only triggers at the exact time the key is pressed while Input.GetButton triggers every frame the key is maintined.

Change the line 60 from if(Input.GetButtonDown("Jump") && !grounded) to if(Input.GetButton("Jump") && !grounded)

Other than that you just have to adjust the lift velocity according to the mass of the rigidbody and the lift velocity that you want.

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LinkUpGames · Sep 19, 2014 at 05:44 PM 0

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Wouldn't that make it so lift only occurs when holding the jump button? I want it to be trigger that occurs when you press the jump key for the allotted time.

dmg0600 · Sep 19, 2014 at 05:53 PM 0

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Ok, I missunderstood. To do so you have to move the rigidbody.AddForce from the if.

 if(Input.GetButtonDown("Jump") && !grounded)
 {
     usingLift = true;
 }
  
 if(usingLift && liftDuration > 0)
 {
     liftDuration -= Time.deltaTime;
 
     rigidbody.AddForce(0, liftVelocity/* * liftDuration*/, 0);
 }

That way when you press jump when in the air, the lift effect is activated by setting the variable usingLift to true.

While it is true and the liftDuration hasn't come to 0, it will reduce the liftDuration and apply the force.

LinkUpGames · Sep 19, 2014 at 06:06 PM 0

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Thanks! Worked perfectly ^-^

dmg0600 · Sep 19, 2014 at 06:17 PM 0

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Glad to hear that! Please mark it as answered. If you have further questions, don't hesitate in asking.

How to AddForce OverTime?

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