Paint Drawing

import flash.display.Sprite;
import flash.events.MouseEvent;

var drawing:Boolean = false;
var erasering:Boolean = false;

var canvas:Sprite = new Sprite();
canvas.graphics.beginFill(0xffffff);
canvas.graphics.drawRect(0, 0, stage.stageWidth, stage.stageHeight);
canvas.graphics.endFill();
addChildAt(canvas, 0);

pencil_mc.addEventListener(MouseEvent.CLICK, pencil);

function pencil(event:MouseEvent)
{
    if(!drawing)
    {
        drawing = true;
        erasering = false;
        pencil_mc.gotoAndStop(2);
        eraser_mc.gotoAndStop(1);
    } else
    {
        drawing = false;
        pencil_mc.gotoAndStop(1);
    }
}

eraser_mc.addEventListener(MouseEvent.CLICK, eraser);

function eraser(event:MouseEvent)
{
    if(!erasering)
    {
        erasering = true;
        drawing = false;
        eraser_mc.gotoAndStop(2);
        pencil_mc.gotoAndStop(1);
    } else
    {
        erasering = false;
        eraser_mc.gotoAndStop(1);
    }
}

canvas.addEventListener(MouseEvent.MOUSE_DOWN, startDraw);

function startDraw(event:MouseEvent)
{
    if(drawing)
    {
        canvas.graphics.lineStyle(2, paletcolor.selectedColor);
        canvas.graphics.moveTo(mouseX, mouseY);
        canvas.addEventListener(MouseEvent.MOUSE_MOVE, movePen);
        canvas.removeEventListener(MouseEvent.MOUSE_MOVE, moveEraser);
    } else if(erasering)
    {
        canvas.graphics.lineStyle(70, 0xffffff);
        canvas.graphics.moveTo(mouseX, mouseY);
        canvas.addEventListener(MouseEvent.MOUSE_MOVE, moveEraser);
        canvas.removeEventListener(MouseEvent.MOUSE_MOVE, movePen);
    }
}

function movePen(event:MouseEvent)
{
    canvas.graphics.lineTo(mouseX, mouseY);
}

function moveEraser(event:MouseEvent)
{
    canvas.graphics.lineTo(mouseX, mouseY);
}

canvas.addEventListener(MouseEvent.MOUSE_UP, stopDraw);

function stopDraw(event:MouseEvent)
{
    if(drawing)
    {
        canvas.graphics.lineTo(mouseX, mouseY);
        canvas.removeEventListener(MouseEvent.MOUSE_MOVE, movePen);
    } else if(erasering)
    {
        canvas.graphics.lineTo(mouseX, mouseY);
        canvas.removeEventListener(MouseEvent.MOUSE_MOVE, moveEraser);
    }
}