Position GameObject sprite where I tap on the screen

Question

I can't do one of the simplest things. When the player taps the screen, I want to put my sprite in that place.

public class Controller : MonoBehaviour {

    public GameObject ball;  // A GameObject with a SpriteRenderer

    void Start () {

    }

    void Update () {
        if (Input.GetMouseButtonDown(0)) {
            ball.transform.position = Input.mousePosition;
        }
    }

}

Well, this doesn't work. When I tap the screen, the sprite appears further up and right. This is how the scene looks:

Where the sprite is by default at (0,0).

Aha, the problem seems quite obvious: if I touch the screen at (0,0) (the bottom-left), the sprite would appear at (0,0) - but as you can see, "(0,0)" is the center of the screen rather than the bottom-left, thus appearing further to the top and right as described above.

The solution seems pretty clear: the position of the sprite should be Input.mousePosition - new Vector3(Screen.width/2, Screen.height/2, 0) to make up for this offset! So:

ball.transform.position = Input.mousePosition - new Vector3(Screen.width/2, Screen.height/2, 0);

... It didn't quite work. Look, if I tap on the top-left of my screen, I get this:

If I tap on the bottom-right:

And if I tap on the center, it works correctly. But that's the only scenario.

---

How can correctly put my sprite wherever I tap on the screen?

Answer 1

Luckily, there's a method for this called Camera.ScreenToWorldPoint. You call it from a camera, pass a Vector3 where the x and y coordinates is the mouse position in pixels and z is the distance from the camera in world units. It then returns a world position as a Vector3.

In your example, you'd probably call it something like this:

const int DistanceFromCamera = 5;
ball.transform.position = Camera.main.ScreenToWorldPoint(Input.mousePosition + DistanceFromCamera * Vector3.forward);