Getting the z of mouse position?

Questions & Answers
1

I’m setting up a “waypoint” system where I click where I want an object to move but when I use:

    private Camera cam;
    Vector3 point = new Vector3();

    Vector3 mousePos = new Vector3();
    public Transform particle;

    void Start()
    {
        cam = Camera.main;
    }

    void OnGUI()
    {
        Event currentEvent = Event.current;
        // Get the mouse position from Event.
        // Note that the y position from Event is inverted.
        mousePos.x = currentEvent.mousePosition.x;
        mousePos.y = cam.pixelHeight - currentEvent.mousePosition.y;
        

        point = cam.ScreenToWorldPoint(new Vector3(mousePos.x, mousePos.y, cam.nearClipPlane));

        GUILayout.BeginArea(new Rect(20, 20, 250, 120));
        GUILayout.Label("Screen pixels: " + cam.pixelWidth + ":" + cam.pixelHeight);
        GUILayout.Label("Mouse position: " + mousePos);
        GUILayout.Label("World position: " + point.ToString("F3"));
        GUILayout.EndArea();
    }

    private void Update()
    {
        if (Input.GetKeyDown("m"))
        {
            Instantiate(particle, point, Quaternion.identity);
        }
    }

from Unity Docs but the z its uses is the camera position. Is there a way to get the z in world space?

2

This is fairly similar to a question I answered earlier today;

https://answers.unity.com/questions/1710147/problem-with-screentoworldpoint-keep-getting-the-s.html?childToView=1710363#answer-1710363

The thing is that expressing the z-coordinate in world space just doesn’t really make sense. The x and y coordinates are in screen-space, so when they are converted to world-space chances are they will write to the z-coordinate as well. If you want to find the coordinates in relation to your world, the ScreenPointToRay function is much more applicable - from there you can either do a physics raycast against scene objects, or a plane raycast if your scene has a specific plane along which you wish to find the point;

//Position of a point that lies on the plane
public Vector3 planePosition = Vector3.zero;
//Rotation in degrees of the plane's normal (where its face is pointing)
public Vector3 planeRotation = new Vector3 (-90f, 0f, 0f);

...

//z-position doesn't matter
Ray ray = cam.ScreenPointToRay (mousePos);
//Create a new plane
Plane plane = new Plane (Quaternion.Euler (planeRotation) * Vector3.forward, planePosition);

//This will raycast against the physical environment, then fall back to the plane if it misses
if (Physics.Raycast (ray, out RaycastHit hit))
{
    point = hit.point;
}
else if (plane.Raycast (ray, out float dist))
{
    point = ray.GetPoint (dist);
}