Camera.ScreenToWorldPoint

function ScreenToWorldPoint (position : Vector3) : Vector3

Description

Transforms position from screen space into world space.

Screenspace is defined in pixels. The bottom-left of the screen is (0,0); the right-top is (pixelWidth,pixelHeight). The z position is in world units from the camera.

JavaScript

// Draw a yellow sphere in the scene view at the position
// on the near plane of the selected camera that is
// 100 pixels from lower-left.
function OnDrawGizmosSelected () {
    var p : Vector3 = camera.ScreenToWorldPoint (Vector3 (100,100,camera.nearClipPlane));
    Gizmos.color = Color.yellow;
    Gizmos.DrawSphere (p, 0.1);
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void OnDrawGizmosSelected() {
        Vector3 p = camera.ScreenToWorldPoint(new Vector3(100, 100, camera.nearClipPlane));
        Gizmos.color = Color.yellow;
        Gizmos.DrawSphere(p, 0.1F);
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def OnDrawGizmosSelected():
        p as Vector3 = camera.ScreenToWorldPoint(Vector3(100, 100, camera.nearClipPlane))
        Gizmos.color = Color.yellow
        Gizmos.DrawSphere(p, 0.1F)