//The maximum depth for the circles
const MAXIMUM_Z:Number = 1500;
 
//Create an array that will contain all the circles
var circles:Array = new Array();
 
//Focal length determines how much perspective is seen (you can play around
//with this value to see the effect yourself).
var focalLength:Number = 300;
 
//Vanishing point is the point where the objects converge.
//So when the object is really far away, it's coordinates
//are almost equal to the vanishing point.
var vanishingPointX:Number = stage.stageWidth / 2;
var vanishingPointY:Number = stage.stageHeight / 2;
 
//The radius of the tunnel
var radius:Number = 120;
 
//The starting depth for the first circle
var startingDepth:Number = MAXIMUM_Z;
 
//The starting angle for the circles
var startingAngle = 0;
 
//Set the angle speed
var angleSpeed:Number = 0.05;
 
//Create a timer which is called every 0.15 seconds
var timer:Timer = new Timer(150,0);
timer.addEventListener(TimerEvent.TIMER, createCircle);
timer.start();
 
function createCircle(e:Event):void {
 
        //Create a new circle
        var circle:MyCircle = new MyCircle();
 
        //Assign a z value for the circle
        circle.zpos3D = MAXIMUM_Z;
 
        //Save the angle for this circle
        circle.currentAngle = startingAngle;
 
        //Set the alpha to 0 at first
        circle.alpha = 0;
 
        //Add the circle on to the stage at the bottom of the display list 
        addChildAt(circle, 0);
 
        //Add ENTER_FRAME for the circle for the animation
        circle.addEventListener(Event.ENTER_FRAME, moveCircle);
}
 
//This function is called in each frame
function moveCircle(e:Event):void {
 
        //Assign the circle to a local variable
        var circle:MyCircle = (MyCircle)(e.target);
 
        //Decrease the depth of the circle (bring the circle closer);
        circle.zpos3D -= 5;
 
        //If zpos3D <= -focalLength, we end up with a negative scaleRatio (or we are dividing by zero).
        //At this point, we know that the object has already passed "us".
        //Therefore, we remove the circle.
        if (circle.zpos3D<=- focalLength) {
 
                //Remove the ENTER_FRAME listener (this function)
                circle.removeEventListener(Event.ENTER_FRAME, moveCircle);
 
                //Remove the circle from stage
                removeChild(circle);
        }
 
        //Update the current angle
        circle.currentAngle+=angleSpeed;
 
        //Calculate a new 3D x position
        circle.xpos3D=Math.cos(circle.currentAngle)*radius;
 
        //Calculate a new 3D y position
        circle.ypos3D=Math.sin(circle.currentAngle)*radius;
 
        //Calculate a scale ratio for the circle
        var scaleRatio = focalLength/(focalLength + circle.zpos3D);
 
        //Scale the circle according to the scale ratio
        circle.scaleX=circle.scaleY=scaleRatio;
 
        //Increase the alpha
        circle.alpha+=0.01;
 
        //Position the circle on to the stage (from 3D to 2D coordinates)
        circle.x=vanishingPointX+circle.xpos3D*scaleRatio;
        circle.y=vanishingPointY+circle.ypos3D*scaleRatio;
}