// Draws a line from "startVertex" var to the curent mouse position.
var mat : Material;
private var startVertex : Vector3;
private var mousePos : Vector3;
startVertex = Vector3(0,0,0);

function Update() {
mousePos = Input.mousePosition;
// Press space to update startVertex
if(Input.GetKeyDown(KeyCode.Space)){
startVertex = Vector3(mousePos.x/Screen.width, mousePos.y/Screen.height, 0);
}
}

function OnPostRender() {
if (!mat) {
Debug.LogError("Please Assign a material on the inspector");
return;
}
GL.PushMatrix();
mat.SetPass(0);
GL.LoadOrtho();
GL.Begin(GL.LINES);
GL.Color(Color.red);
GL.Vertex(startVertex);
GL.Vertex(Vector3(mousePos.x/Screen.width, mousePos.y/Screen.height, 0));
GL.End();
GL.PopMatrix();
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
public Material mat;
private Vector3 startVertex;
private Vector3 mousePos;
void Update() {
mousePos = Input.mousePosition;
if (Input.GetKeyDown(KeyCode.Space))
startVertex = new Vector3(mousePos.x / Screen.width, mousePos.y / Screen.height, 0);

}
void OnPostRender() {
if (!mat) {
Debug.LogError("Please Assign a material on the inspector");
return;
}
GL.PushMatrix();
mat.SetPass(0);
GL.LoadOrtho();
GL.Begin(GL.LINES);
GL.Color(Color.red);
GL.Vertex(startVertex);
GL.Vertex(new Vector3(mousePos.x / Screen.width, mousePos.y / Screen.height, 0));
GL.End();
GL.PopMatrix();
}
void Awake() {
startVertex = new Vector3(0, 0, 0);
}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

public mat as Material

private startVertex as Vector3

private mousePos as Vector3

def Update():
mousePos = Input.mousePosition
if Input.GetKeyDown(KeyCode.Space):
startVertex = Vector3((mousePos.x / Screen.width), (mousePos.y / Screen.height), 0)

def OnPostRender():
if not mat:
Debug.LogError('Please Assign a material on the inspector')
return
GL.PushMatrix()
mat.SetPass(0)
GL.LoadOrtho()
GL.Begin(GL.LINES)
GL.Color(Color.red)
GL.Vertex(startVertex)
GL.Vertex(Vector3((mousePos.x / Screen.width), (mousePos.y / Screen.height), 0))
GL.End()
GL.PopMatrix()

def Awake():
startVertex = Vector3(0, 0, 0)