Plus and minus instead of mouse pointer

Question

http://www.rwphotographic.com/#/recent/pbs
On the site above, the designer has managed to replace the mouse pointer with a plus (+) or minus (-) depending on where the mouse pointer is (either the left hand side of the screen or the right).
I'd like to know how I could achieve this via AS3, if this is a possibility.
It will still need to work when the browser is resized however.
Thanks if you can help.

Answer 1

This code shows either plus or minus depending over which half of green rectangle mouse is:
import flash.events.MouseEvent;
import flash.ui.Mouse;
var plus:Shape = makePlus();
var minus:Shape = makeMinus();
var sprite:Sprite = new Sprite();
var g:Graphics = sprite.graphics;
g.beginFill(0x008040);
g.drawRect(0, 0, 200, 200);
g.endFill();
addChild(sprite);
sprite.x = sprite.y = 50;
var spritVerticalCenter:Number = sprite.x + sprite.width * .5;
sprite.addEventListener(MouseEvent.MOUSE_OVER, onSpriteOver);
sprite.addEventListener(MouseEvent.MOUSE_OUT, onSpriteOut);
onSpriteOut();
function onSpriteOut(e:MouseEvent = null):void
     Mouse.show();
     plus.visible = false;
     minus.visible = false;
     stage.removeEventListener(MouseEvent.MOUSE_MOVE, onMouseMove);
function onSpriteOver(e:MouseEvent):void
     Mouse.hide();
     addChild(plus);
     addChild(minus);
     stage.addEventListener(MouseEvent.MOUSE_MOVE, onMouseMove);
     onMouseMove();
function onMouseMove(e:MouseEvent = null):void
     plus.x = minus.x = mouseX;
     plus.y = minus.y = mouseY;
     plus.visible = mouseX > spritVerticalCenter;
     minus.visible = mouseX < spritVerticalCenter;
function makePlus():Shape {
     var s:Shape = new Shape();
     var g:Graphics = s.graphics;
     g.lineStyle(4, 0xff0000);
     g.moveTo( -8, 0);
     g.lineTo(8, 0);
     g.moveTo(0, -8);
     g.lineTo(0, 8);
     return s;
function makeMinus():Shape {
     var s:Shape = new Shape();
     var g:Graphics = s.graphics;
     g.lineStyle(4, 0xff0000);
     g.moveTo( -8, 0);
     g.lineTo(8, 0);
     return s;