AS3 drag mc but inside another mc or other object and cut when goes out

Question

What is easiest way to do this:

on stage 400x400 I have rect 200x200, inside rect are few mc objects. I can drag & drop StartDrag and add 200x200 as limits for this movement, but how I can do that when drag obejct they can be "visible" just near the border of rect, in other words if I drag circle into 200x200 rectangle how to make "disappear" part of that circle when it touch the border of 200x200 rect?

Answer 1

You need to add a mask to the circle. Here would be an example for the above scenario:

var squareBG:Shape = new Shape();
squareBG.graphics.beginFill(0);
squareBG.graphics.drawRect(0,0,200,200);
squareBG.graphics.endFill();
addChild(squareBG);

var circle:Sprite = new Sprite();
circle.graphics.beginFill(0xFF0000);
circle.graphics.drawCircle(0,0,100);
circle.graphics.endFill();
circle.y = 125;
addChild(circle);

var circle2:Sprite = new Sprite();
circle2.graphics.beginFill(0xFFFF00);
circle2.graphics.drawCircle(0,0,100);
circle2.graphics.endFill();
addChild(circle2);
circle2.x = 150;

var myMask:Shape = new Shape();
myMask.graphics.copyFrom(squareBG.graphics);    
addChild(myMask);

var myMask2:Shape = new Shape();
myMask2.graphics.copyFrom(squareBG.graphics);    
addChild(myMask2);

circle.mask = myMask;
circle2.mask = myMask2;