ActionScript 3.0 Cookbook: Chapter 6, Display List
Pages: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

Using these events is simply a matter of calling addEventListener( ) on the InteractiveObject and defining an event handler to handle the MouseEvent passed to it.

The following code snippet creates a Sprite, draws a red circle inside of it, and outputs a message to the console whenever the mouse moves over the circle:

package {
  import flash.display.Sprite;
  import flash.events.*;
  import flash.geom.Point;

  public class InteractiveMouseDemo extends Sprite {
    public function InteractiveMouseDemo( ) {
      var circle:Sprite = new Sprite( );
      circle.x = 10;
      circle.y = 10;
      circle.graphics.beginFill( 0xFF0000 );
      circle.graphics.drawCircle( 0, 0, 5 );
      circle.graphics.endFill( );
      
      circle.addEventListener( MouseEvent.MOUSE_MOVE, handleMouseMove );

      addChild( circle );
    }
    
    // Event handle to capture the move event over the circle
    private function handleMouseMove( event:MouseEvent ):void {
      trace( "mouse move" );
    }
  }
}

In this example, notice that the message appears only when the mouse is moved while the pointer is over the circle. The circle defines the bounds for the Sprite in this case.

Mouse events are generated from a particular interactive display object only when the pointer is within the bounds of that object.

Another common use of mouse events stems from wanting to inspect the location of the mouse pointer to create mouse interactivity. For example, to draw a line with the mouse, the mouse location needs to be known so the line can be plotted accurately. There are two ways to determine the location of the mouse pointer:

• Using the mouseX and mouseY properties available on any DisplayObject instance.
• Using the localX and localY properties available from the MouseEvent instance passed to the mouse event handler.

The mouseX and mouseY properties can be inspected to determine the location of the mouse cursor relative to the top-left corner of the DisplayObject. Both of the properties are read-only; it is not possible to set the location of the mouse cursor, only to examine the location.

So, imagine that a rectangle is at x location 20 and y location 50 and the user moves the mouse pointer to x location 25 and y location 60. The mouseX property of the rectangle returns 5 and mouseY of the rectangle reports 10 because from the rectangle's perspective, the mouse is 5 pixels in from the left and 10 pixels down from the top.

The localX and localY properties of the MouseEvent are also relative. In the MouseEvent case, the properties are relative to interactive display object that dispatched the event. Therefore, consider that a rectangle reports mouseX of 10 and dispatches a mouseMove event. The event's localX property is also 10.

To get the global position of the mouse from local coordinates, use the localToGlobal( ) method of the DisplayObject class. The localToGlobal( ) method takes flash.geom.Point as a parameter that specifies the local coordinates, and returns a new Point with the coordinates converted to the global space. The following code snippet focuses on the event handler and demonstrates how to convert localX and localY to global coordinates:

// Event handler to respond to a mouseMove event
private function handleMouseMove( event:MouseEvent ):void {
  /* Displays:
  local x: 3.95
  local y: 3.45
  */
  trace( "local x: " + event.localX );
  trace( "local y: " + event.localY );
  
  // Create the point that localToGlobal should convert
  var localPoint:Point = new Point( event.localX, event.localY );
  // Convert from the local coordinates of the display object that
  // dispatched the event to the global stage coordinates
  var globalPoint:Point = event.target.localToGlobal( localPoint );
  
  /* Displays:
  global x: 13.95
  global y: 13.45
  */
  trace( "global x: " + globalPoint.x );
  trace( "global y: " + globalPoint.y );
}

This excerpt is from ActionScript 3.0 Cookbook. Well before Ajax and Windows Presentation Foundation, Macromedia Flash provided the first method for building "rich" web pages. Now, Adobe is making Flash a full-fledged development environment, and learning ActionScript 3.0 is key. That's a challenge for even the most experienced Flash developer. This Cookbook offers more than 300 solutions to solve a wide range of coding dilemmas, so you can learn to work with the new version right away.

A complete working example of creating interactivity through handling the various mouse events can be demonstrated by the simple drawing program that follows. Whenever the mouse is pressed, the drawing starts. As the user moves the mouse around the screen, a line is drawn that follows the movement of the mouse pointer. When the user releases the mouse button, the drawing stops:

package {
  import flash.display.Sprite;
  import flash.events.MouseEvent;
  public class DrawingDemo extends Sprite {
    
    // Flag to indicate whether the mouse is in draw mode
    private var _drawing:Boolean;
    
    public function DrawingDemo( ) {
      // Configure the line style
      graphics.lineStyle( 2, 0xFFCC33 );
      
      // Drawing is false until the user presses the mouse
      _drawing = false;
      
      // Add the mouse listeners on the stage object to be 
      // notfied of any mouse event that happens while the 
      // mouse is over the entire movie
      stage.addEventListener( MouseEvent.MOUSE_DOWN, startDrawing );
      stage.addEventListener( MouseEvent.MOUSE_MOVE, draw );
      stage.addEventListener( MouseEvent.MOUSE_UP, stopDrawing );
    }
    
    public function startDrawing( event:MouseEvent ):void {
      // Move to the current mouse position to be ready for drawing
      graphics.moveTo( mouseX, mouseY );
      _drawing = true;
    }
    
    public function draw( event:MouseEvent ):void {
      if ( _drawing ) {
        // Draw a line from the last mouse position to the 
        // current one
        graphics.lineTo( mouseX, mouseY );  
      }
    }
    
    public function stopDrawing( event:MouseEvent ):void {
      _drawing = false;
    }
    
  }
}

See Also

Recipes 6.4 and 6.8

Share your knowledge with the Digital Media community!
You must be logged in to the O'Reilly Network to post a talkback.