ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Display programming
// This function is called every time the mouse moves,
// as long as the mouse button is pressed down.
function dragObject(event:MouseEvent):void
{
// Move the dragged object to the location of the cursor, maintaining
// the offset between the cursor's location and the location
// of the dragged object.
draggedObject.x = event.stageX - offsetX;
draggedObject.y = event.stageY - offsetY;
}
// Instruct Flash Player to refresh the screen after this event.
event.updateAfterEvent();
circle.addEventListener(MouseEvent.MOUSE_DOWN, startDragging);
circle.addEventListener(MouseEvent.MOUSE_UP, stopDragging);
square.addEventListener(MouseEvent.MOUSE_DOWN, startDragging);
square.addEventListener(MouseEvent.MOUSE_UP, stopDragging);
To extend this effect further, such as for a game where tokens or cards are moved among piles, you could add the
dragged object to the Stage’s display list when it’s “picked up,” and then add it to another display list—such as the “pile”
where it is dropped—when the mouse button is released.
Finally, to enhance the effect, you could apply a drop shadow filter to the display object when it is clicked (when you
start dragging it) and remove the drop shadow when the object is released. For details on using the drop shadow filter
and other display object filters in ActionScript, see “Filtering display objects” on page 267.
Panning and scrolling display objects
Flash Player 9 and later, Adobe AIR 1.0 and later
If you have a display object that is too large for the area in which you want it to display it, you can use the scrollRect
property to define the viewable area of the display object. In addition, by changing the scrollRect property in
response to user input, you can cause the content to pan left and right or scroll up and down.
The scrollRect property is an instance of the Rectangle class, which is a class that combines the values needed to
define a rectangular area as a single object. To initially define the viewable area of the display object, create a new
Rectangle instance and assign it to the display object’s scrollRect property. Later, to scroll or pan, you read the
scrollRect property into a separate Rectangle variable, and change the desired property (for instance, change the
Rectangle instance’s x property to pan or y property to scroll). Then you reassign that Rectangle instance to the
scrollRect property to notify the display object of the changed value.
For example, the following code defines the viewable area for a TextField object named bigText that is too tall to fit
in the SWF file’s boundaries. When the two buttons named up and down are clicked, they call functions that cause the
contents of the TextField object to scroll up or down by modifying the y property of the scrollRect Rectangle
instance.
Last updated 6/6/2012
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