How to make a Mask in AS3 - actionscript-3

Question

I have a duvifa that is:
I wonder if it is possible to make a mask in a movieClip the way it is below:
If this image would be the beginning of the game.
When the user clicks on the screen, a type of cream would be created, but not like he would extend all over the stage, but only in my way.
As below:
And also like to know if I can get a percentage of what was filled in the form, to see if the user has filled at least 40%.
Thank U.

Answer 1

Here is a quick example using flashPro, assuming you have your shape graphic as an import .png library object with an export for actionscript class of MC.
import flash.display.Shape;
import flash.events.Event;
import flash.display.BlendMode;
var mc:MC = new MC(); //the background image
addChild(mc);
var drawing:Shape = new Shape(); //drawing foreground
addChild(drawing);
var mcMask:MC = new MC(); //mask version of background image
addChild(mcMask);
var outerMask:Shape = new Shape(); //this object masks the areas outside the bounds of mcMask object
outerMask.graphics.beginFill(0);
outerMask.graphics.drawRect(0,0,mcMask.width,mcMask.height);
outerMask.graphics.endFill();
addChild(outerMask);
drawing.mask = outerMask; //the mask to the shape whose dimensions equal the image mask
mcMask.blendMode = BlendMode.ALPHA; //this tells the mask graphic to make things underneath it use the same alpha data as this image. This works will with PNG masks.
this.blendMode = BlendMode.LAYER; //the parent needs to have a blend mode of LAYER for it to work properly
stage.addEventListener(MouseEvent.MOUSE_MOVE,draw);
function draw(e:Event):void {
trace("draw");
drawing.graphics.beginFill(0x0000FF);
drawing.graphics.drawCircle(mouseX,mouseY,10);
drawing.graphics.endFill();
}