How to apply force to mouse position?

ramonfr · December 12, 2011, 12:46am

I’m building a soccer game. Once the player has the ball, he is able to kick it to the mouse coordinates.

The problem is:

1 - Once the player has the ball ( “carrying the ball” problem already solved ), when the player clicks on a point of the screen, the ball ( which is a rigidbody ) has to be kicked to this point.

My questions are:

1 - I can’t find out how to solve it. Converting 2D coordinates to an 3D space is a mystery to me ( However, I created an sphere which follows the mouse coordinates, so the ball could simply be kicked to the direction of this object in the 3D plane ).

2 - I can’t get how to make the rigid.addForce look realistic, like an impulse, how it should be. How can I use the force mode “Impulse”?

aldonaletto · December 12, 2011, 2:07am

Impulse mode adds an instant velocity to the rigidbody in the following proportion: velAdded = force/rigidbody.mass. Physically, it applies instantly the acceleration that the force would produce during one second. It’s the best solution in your case, because it will reproduce physically a kick effect even if the ball has an initial velocity in any direction.

You can convert mouse coordinates to world point using Input.mousePosition, ScreenPointToRay and Physics.Raycast, then calculate the desired direction and apply the force:

var ball: Transform; // drag the ball here
var force: float = 50; // change the force when needed

function Update () {
  if (Input.GetButtonDown("Fire1")){
    // Create a ray from the current mouse coordinates
    var ray: Ray = Camera.main.ScreenPointToRay(Input.mousePosition);
    var hit: RaycastHit;
    // if something tagged "Ground" is hit...
    if (Physics.Raycast(ray, hit) && hit.transform.tag == "Ground"){
      var dir = hit.point - ball.position; // calculated the direction...
      // and kick!
      ball.rigidbody.AddForce(dir.normalized * kickForce, ForceMode.Impulse);
    }
  }
}

IMPROVED VERSION: The script above kicks the ball in the clicked point direction, but the force must be controlled somehow by the player to make the ball reach the desired point, and you have no control over the elevation angle. If you want the ball to fall precisely in the clicked point, you can use the version below, where the function KickForce calculates the desired force and direction:

var ball: Transform; // drag the ball here

function KickForce(dest: Vector3, angle: float): Vector3 {
  var dir = dest - ball.position;  // get target direction
  var h = dir.y;  // get height difference
  dir.y = 0;  // retain only the horizontal direction
  var dist = dir.magnitude ;  // get horizontal distance
  var a = angle * Mathf.Deg2Rad;  // convert angle to radians
  dir.y = dist * Mathf.Tan(a);  // set dir to the elevation angle
  dist += h / Mathf.Tan(a);  // correct for small height differences
  // calculate the velocity magnitude
  var vel = Mathf.Sqrt(dist * Physics.gravity.magnitude / Mathf.Sin(2 * a));
  return vel * dir.normalized * ball.rigidbody.mass;
}

// control the kick angle when needed: the greater the angle, the slower the kick
var kickAngle: float = 15;

function Update(){
  if (Input.GetButtonDown("Fire1")){
    // Create a ray from the current mouse coordinates
    var ray: Ray = Camera.main.ScreenPointToRay(Input.mousePosition);
    var hit: RaycastHit;
    // if something tagged "Ground" is hit...
    if (Physics.Raycast(ray, hit) && hit.transform.tag == "Ground"){
      var kForce = KickForce(hit.point, kickAngle); // calculate the force and kick!
      ball.rigidbody.AddForce(kForce, ForceMode.Impulse);
    }
  }
}

NOTE: The current ball velocity will be added to the kick velocity, thus the destination point may not be reached; if this is the case, replace the last Update() line with ball.rigidbody.velocity = kForce; and remove the ball.rigidbody.mass from the last KickForce() line.

alok-kr-029 · January 18, 2014, 4:09am

#pragma strict
var ball: Transform; // drag the ball here
var play : boolean =false;

function KickForce(dest: Vector3, angle: float): Vector3 {
var dir = dest - ball.position; // get target direction
var h = dir.y; // get height difference
dir.y = 0; // retain only the horizontal direction
var dist = dir.magnitude ; // get horizontal distance
var a = angle * Mathf.Deg2Rad; // convert angle to radians
dir.y = dist * Mathf.Tan(a); // set dir to the elevation angle
dist += h / Mathf.Tan(a); // correct for small height differences
// calculate the velocity magnitude
var vel = Mathf.Sqrt(dist * Physics.gravity.magnitude / Mathf.Sin(2 * a));
return vel * dir.normalized * ball.rigidbody.mass;
}

// control the kick angle when needed: the greater the angle, the slower the kick
var kickAngle: float = 15;

if(Input.GetMouseButtonDown(0)){

}
}