Mouse Drawing in Unity3D

using UnityEngine;
using System.Collections;

public class Paint : MonoBehaviour {
	Texture2D tex;
	// Use this for initialization
	void Start () {
		tex = new Texture2D(128, 128);
		GameObject.Find("Plane").renderer.sharedMaterial.mainTexture = tex;
	}
	
	void Update () {
		if (tex != null)
		{
			Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
			RaycastHit hit;
			if (Input.GetButton("Fire1"))
			{
				if (Physics.Raycast (ray, out hit, Mathf.Infinity))
				{
					// Find the u,v coordinate of the Texture
					Vector2 uv;
					uv.x = (hit.point.x - hit.collider.bounds.min.x) / hit.collider.bounds.size.x;
					uv.y = (hit.point.y - hit.collider.bounds.min.y) / hit.collider.bounds.size.y;
					// Paint it red
					tex.SetPixel ((int)(-uv.x * tex.width), (int)(uv.y * tex.height), Color.red);
					tex.SetPixel ((int)(-uv.x * tex.width), (int)(uv.y * tex.height) + 1, Color.red);
					tex.SetPixel ((int)(-uv.x * tex.width) + 1, (int)(uv.y * tex.height), Color.red);
					tex.SetPixel ((int)(-uv.x * tex.width), (int)(uv.y * tex.height) - 1, Color.red);
					tex.SetPixel ((int)(-uv.x * tex.width) - 1, (int)(uv.y * tex.height), Color.red);
					tex.SetPixel ((int)(-uv.x * tex.width) + 1, (int)(uv.y * tex.height) + 1, Color.red);
					tex.SetPixel ((int)(-uv.x * tex.width) - 1, (int)(uv.y * tex.height) - 1, Color.red);
					tex.SetPixel ((int)(-uv.x * tex.width) - 1, (int)(uv.y * tex.height) + 1, Color.red);
					tex.SetPixel ((int)(-uv.x * tex.width) + 1, (int)(uv.y * tex.height) - 1, Color.red);
					tex.Apply ();
				}
			}
			if (Input.GetButton("Fire2"))
			{
				for (int i = 0; i < 128; i++)
				{
					for (int j = 0; j < 128; j++)
					{
						tex.SetPixel(i,j, Color.white);
					}
				}
				tex.Apply();
			}
		}
	}
}