package {
    import flash.display.*;
    import flash.events.*;
    import flash.ui.*;
    import flash.geom.*;
  
    // A basic drawing application. Draws a single dot on a
    // BitmapData object every time the MouseEvent.MOUSE_MOVE event 
    // occurs while the primary mouse button is depressed.
    public class @ax-actionscript-scribble-ScribbleAS3 extends Sprite {
      // The on-screen bitmap
      private var canvas:Bitmap;  
      // Contains the bitmap, providing interactivity
      private var canvasContainer:Sprite;  
      // Line around the bitmap
      private var border:Shape;  
      // Indicates whether the mouse is currently depressed
      private var isDrawing:Boolean = false;  
      
      // Constructor
      public function @ax-actionscript-scribble-ScribbleAS3 () {
        createCanvas();
        registerForInputEvents();
       
        // Prevent the app from resizing
        stage.scaleMode = StageScaleMode.NO_SCALE;
      }
      
      // Creates the empty bitmap object where drawing will occur
      private function createCanvas (width:int = 200, height:int = 200):void {
        // Define the BitmapData object that will store the pixel 
        // data for the user's drawing
        var canvasData:BitmapData = new BitmapData(width, height, 
                                                   false, 0xFFFFFFFF);
        
        // Create a new displayable Bitmap, used to render the
        // canvasData object
        canvas = new Bitmap(canvasData);
        
        // Create a Sprite to contain the Bitmap. The Bitmap class doesn't
        // support input events; hence, put it in a Sprite so the user 
        // interact with it.
        canvasContainer = new Sprite();
        // Add the canvas bitmap to the canvasContainer Sprite
        canvasContainer.addChild(canvas);
        
        // Add the canvasContainer Sprite (and the Bitmap it contains) to
        // this object's display hierarchy
        addChild(canvasContainer);
  
        // Make a border around the drawing surface
        border = new Shape();
        border.graphics.lineStyle(1, 0xFF000000);
        border.graphics.drawRect(0, 0, width, height);
        addChild(border);
      }
      
      // Registers for the required mouse and keyboard events
      private function registerForInputEvents ():void {
        // Register for mouse down and movement events from canvasContainer
        canvasContainer.addEventListener(MouseEvent.MOUSE_DOWN, 
                                         mouseDownListener);
        canvasContainer.addEventListener(MouseEvent.MOUSE_MOVE,
                                         mouseMoveListener);
  
        // Register for mouse up and key events from the Stage (i.e., 
        // globally). Use the Stage because a mouse up event should always 
        // exit drawing mode, even if it occurs while the mouse pointer is 
        // not over the drawing. Likewise, the spacebar should always clear 
        // the drawing, even when canvasContainer isn't focused. 
        stage.addEventListener(MouseEvent.MOUSE_UP, mouseUpListener);
        stage.addEventListener(KeyboardEvent.KEY_DOWN, keyDownListener);
      }
  
      // Sets the color of a specified pixel
      public function drawPoint (x:int, y:int, color:uint = 0xFF000000):void {
        canvas.bitmapData.setPixel32(x, y, color);
      }
  
      // Responds to MouseEvent.MOUSE_DOWN events
      private function mouseDownListener (e:MouseEvent):void {
        // Set a flag indicating that the primary 
        // mouse button is currently down
        isDrawing = true;
        // Draw a dot where the mouse was clicked. 
        drawPoint(e.localX, e.localY);
      }
  
      // Responds to MouseEvent.MOUSE_MOVE events
      private function mouseMoveListener (e:MouseEvent):void {
        // Draw a dot when the mouse moves over the drawing
        // while the primary mouse button is depressed
        if (isDrawing) {
          // Use localX and localY to obtain pointer position relative to 
          // the canvasContainer.
          drawPoint(e.localX, e.localY);
          
          // Update the screen immediately following the execution of
          // this event listener function
          e.updateAfterEvent();
        }
      }
  
      // Responds to MouseEvent.MOUSE_UP events
      private function mouseUpListener (e:MouseEvent):void {
        // Set a flag indicating that the primary mouse button is currently up
        isDrawing = false;
      }
  
      // Responds to KeyboardEvent.KEY_DOWN events
      private function keyDownListener (e:KeyboardEvent):void {
        // Clear the drawing when the spacebar is pressed. To clear the
        // drawing, we set all pixels to the color white.
        if (e.charCode == Keyboard.SPACE) {
          canvas.bitmapData.fillRect(new Rectangle(0, 0,
                                                 canvas.width, canvas.height), 
                                     0xFFFFFFFF);
        }
      }
    }
  }