Transforms position from viewport space into world space.

Viewport space is normalized and relative to the camera. The bottom-left of the camera is (0,0); the top-right is (1,1). The z position is in world units from the camera.

Note that it transforms a x-y screen position, into a x-y-z position in 3D space.

You provide the function with a vector where the x-y components of the vector are the screen coordinates and the z component is the distance of the resulting plane from the camera.

	// Draw a yellow sphere at top-right corner of the near plane
	// for the selected camera in the scene view.
	function OnDrawGizmosSelected () {
		var p : Vector3 = camera.ViewportToWorldPoint (Vector3 (1,1, 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.ViewportToWorldPoint(new Vector3(1, 1, camera.nearClipPlane));
        Gizmos.color = Color.yellow;
        Gizmos.DrawSphere(p, 0.1F);
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def OnDrawGizmosSelected() as void:
		p as Vector3 = camera.ViewportToWorldPoint(Vector3(1, 1, camera.nearClipPlane))
		Gizmos.color = Color.yellow
		Gizmos.DrawSphere(p, 0.1F)