drawing a grid crahes editor and game.

hi all. i've got code to draw a grid. which crashes may game. plus causes the editor to do the same when loading up as default scene.

if anyone can see whats wrong, please let me know.


using UnityEngine;
using System.Collections;

[ExecuteInEditMode]
public class DrawGrid : MonoBehaviour
{
// When added to an object, draws colored rays from the
// transform position.
public float positiontop;
public float positionbottom;
public float positionfromleft;
public float positionfromright;
public int rows;
public int collumns;

float positionleft;
float positionright;

static Material lineMaterial;

static void CreateLineMaterial ()
{
if (!lineMaterial)
{
// Unity has a built-in shader that is useful for drawing
// simple colored things.
var shader = Shader.Find ("Hidden/Internal-Colored");
lineMaterial = new Material (shader);
lineMaterial.hideFlags = HideFlags.HideAndDontSave;
// Turn on alpha blending
lineMaterial.SetInt ("_SrcBlend", (int)UnityEngine.Rendering.BlendMode.SrcAlpha);
lineMaterial.SetInt ("_DstBlend", (int)UnityEngine.Rendering.BlendMode.OneMinusSrcAlpha);
// Turn backface culling off
lineMaterial.SetInt ("_Cull", (int)UnityEngine.Rendering.CullMode.Off);
// Turn off depth writes
lineMaterial.SetInt ("_ZWrite", 0);
}
}

public void Update()
{
float vert = Camera.main.GetComponent<Camera>().orthographicSize;

positionleft = -(vert * Screen.width / Screen.height);
positionright = -positionleft;

positionleft += positionfromleft;
positionright -= positionfromright;
}

// Will be called after all regular rendering is done
public void OnRenderObject ()
{
CreateLineMaterial ();
// Apply the line material
lineMaterial.SetPass (0);

GL.PushMatrix ();
// Set transformation matrix for drawing to
// match our transform
//GL.MultMatrix (transform.localToWorldMatrix);

// Draw lines
GL.Begin (GL.LINES);

GL.Color (new Color (1, 1, 1, 1));

float width = positionright - positionleft;
float heigt = positiontop - positionbottom;
float boxwidth = width / collumns;
float boxheight = heigt / rows;

//draw grid vertical
for(float x = positionleft; x <= positionright; x += boxwidth)
{
GL.Vertex3 (x, positiontop, 0);
GL.Vertex3 (x, positionbottom, 0);
}

//draw grid horizontal
for(float y = positionbottom; y <= positiontop; y += boxheight)
{
GL.Vertex3 (positionleft, y, 0);
GL.Vertex3 (positionright, y, 0);
}

GL.End ();
GL.PopMatrix ();
}
}