How to use a movieclip as a boundary for another dragable object in AS3? - actionscript-3

Question

How to use a movieclip as a boundary for another dragable object?
All I know is, we can use a rectangle for boundary in start drag .
dragable_mc.addEventListener(MouseEvent.MOUSE_DOWN, start_drag);
function start_drag(e:MouseEvent)
{
var rect:Rectangle = new Rectangle(0,0,100,100);
dragable_mc.startDrag(false, rect);
}
What is the way to drag a movieclip in another movieclip in flash by as3?
(like as I shown in pic)

Answer 1

If it is a dynamic shape, you'd have to log the x,y coordinates of the drag-able object every frame upon drag. Then do a bitmap-hitpoint test with the boundary to check if the object is out of bounds. If it is outside, return to the last coordinates that isn't out of bound.
edit:
The two variables you need to rename are dragTarget and bound_mc
dragTarget is your dragable_mc
bound_mc is the name of the movieclip of your boundary.
bound_mc need to be in png format, and the out of bounds area MUST be transparent. example:
import flash.geom.Point;
import flash.geom.Rectangle;
import flash.events.MouseEvent;
import flash.events.Event;
import flash.display.BitmapData;
stop();
var bmd:BitmapData =new BitmapData(600, 400, true, 0x000000);
var rect:Rectangle;
var lastPt:Point = new Point();
function init():void {
rect = new Rectangle(0, 0, stage.stageWidth, stage.stageHeight);
setUpBitmap();
}
function setUpBitmap():void {
bmd.draw(bound_mc);
dragTarget.addEventListener(MouseEvent.MOUSE_DOWN, start_drag);
}
function start_drag(event:MouseEvent):void {
dragTarget.removeEventListener(MouseEvent.MOUSE_DOWN, start_drag);
stage.addEventListener(MouseEvent.MOUSE_UP, stop_drag);
lastPt.x = dragTarget.x;
lastPt.y = dragTarget.y;
dragTarget.startDrag(false, rect);
this.addEventListener(Event.ENTER_FRAME, logPoint);
}
function stop_drag(event:MouseEvent):void {
this.removeEventListener(Event.ENTER_FRAME, logPoint);
stage.removeEventListener(MouseEvent.MOUSE_UP, stop_drag);
dragTarget.addEventListener(MouseEvent.MOUSE_DOWN, start_drag);
dragTarget.stopDrag();
}
function logPoint(event:Event):void {
var curPoint:Point = new Point(stage.mouseX, stage.mouseY);
if ( bmd.hitTest(new Point( bound_mc.x, bound_mc.y ), 0, curPoint) ) {
lastPt = curPoint;
} else {
dragTarget.x = lastPt.x;
dragTarget.y = lastPt.y;
stage.dispatchEvent(new MouseEvent(MouseEvent.MOUSE_UP));
}
}
init();