Firing rigidbody in an arc given the beginning and middle of arc

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1

Here is the updated code, unfortunately when i release my finger from the screen nothing happens :frowning: any help is appreciated.

#pragma strict

var startpos : Vector3;
var mousePos : Vector3;

function Update () {
    for(var touch : Touch in Input.touches)
    {
        if(touch.phase == TouchPhase.Began)
        {
            mousePos = touch.position;
        }
        else if(touch.phase == TouchPhase.Moved)
        {
            mousePos = touch.position;
        }
        else if(touch.phase == TouchPhase.Ended)
        {
            var pos = mousePos;
            var startpos = transform.position; // get the initial position 
            // create a plane at startpos and perpendicular to the camera:
            var plane = new Plane(-Vector3.forward, startpos);
            // create a ray from the touch point:
            var ray: Ray = Camera.main.ScreenPointToRay(pos);
            var dist: float;
            plane.Raycast(ray, dist); // cast the ray to the plane
            var apex: Vector3 = ray.GetPoint(dist); // find the hit point
            var delta: Vector3 = apex-startpos; // delta.y = apex height
            var g = -Physics.gravity.y; // g is the gravity absolute value
            var vel = Vector3.zero; // calculate the velocity needed:
            vel.y = Mathf.Sqrt(2.0*g*delta.y); // vertical velocity
            vel.x = delta.x/(vel.y/g); // horizontal velocity
            rigidbody.velocity = vel; // fire the rigidbody
        }
    }
}

1 Answer

1
2

There’s a problem in your code: you’re mixing screen coordinates (mousepos) and world space (startpos). You must convert the touch position to the world space: assuming that world Y is the vertical direction, X is horizontal and Z points to the screen, you could create a plane passing through the start object, do a raycast from the touch position and find where it intersects the plane - this is the apex point. Having the startpos and the apex, you can calculate the necessary vertical velocity to reach the apex point. With this velocity, you can find the time needed to reach it, and calculate the horizontal velocity. A piece of cake, no?

In practice, the whole thing would become something like this:

function Update () {
  if (Input.touchCount>0){ // if any touche...
    var touch: Touch = Input.touches[0]; // get the first one
    switch (touch.phase){
      case TouchPhase.Began:
      case TouchPhase.Moved:
        var mousepos = touch.position;
        break;
      case TouchPhase.Ended:
        Shoot(mousePos);
    }
  }
}

function Shoot(pos: Vector2){
  var startpos = transform.position; // get the initial position 
  // create a plane at startpos and perpendicular to the camera:
  var plane = new Plane(-Vector.forward, startpos);
  // create a ray from the touch point:
  var ray: Ray = Camera.main.ScreenPointToRay(pos);
  var dist: float;
  plane.Raycast(ray, dist); // cast the ray to the plane
  var apex: Vector3 = ray.GetPoint(dist); // find the hit point
  var delta: Vector3 = apex-startpos; // delta.y = apex height
  var g = -Physics.gravity.y; // g is the gravity absolute value
  var vel = Vector3.zero; // calculate the velocity needed:
  vel.y = Mathf.Sqrt(2.0*g*delta.y); // vertical velocity
  vel.x = delta.x/(vel.y/g); // horizontal velocity
  rigidbody.velocity = vel; // fire the rigidbody
}

NOTE 1: The touch code wasn’t tested (I don’t have an Android device);

NOTE 2: The vertical velocity is calculated from the energy formula: m.v2/2 = m.g.h, what becomes vel.y = sqrt(2gh). Since at the apex the vertical velocity was consumed by the gravity, the time t to reach it is vel.y/g, and the horizontal velocity should be vel.x/t.