How to have an object hover back and forth constrained within a specific radius? - actionscript-3

Question

I have a sprite in a movie symbol that I would like to hover back and forth within a 360 radius. I was hoping to make it smooth and random. Never really venturing from its original xy cordinates.
I've tried to create some stipulations with if statements and a starting momentum. Like this:
var num = 2;
stage.addEventListener(Event.ENTER_FRAME, hover);
function hover(evt:Event):void{
//start it moving
cloudWhite.y += num;
cloudWhite.x += num;
//declare these variables
var cX = cloudWhite.x;
var cY = cloudWhite.y;
// object travels 10 pixels
var cXP = cX + 10;
var cXN = cX - 10;
var cYP = cY + 10;
var cYN = cY - 10;
// if object goes 10 pixels reverse direction of momentum (maybe)
if (cX >= cXP) {
num = -2;
}
if (cX <= cXN){
num = 2;
}
if (cY >= cYP) {
num = 2;
}
if (cY <= cYN){
num = 2;
}
Clearly this is super wrong because when it runs the object just either goes to 0,0 or to some place that only the math gods know of.
I am clearly a noob at this kind of math so i apologize but I am very excited to learn the trig behind this.
Thank you for your help and thank you for reading.

Answer 1

You are setting all your variables inside the ENTER_FRAME loop, so none of your conditions ever evaluates to true. On every single frame you are doing this:
cloudWhite.x += 2;
cX = cloudWhite.x;
cXP = cX + 10; // Must == cloudWhite's previous x + 10 + 2;
cXN = cX - 10; // Must == cloudWite's previous x -10 + 2;
if(cX > cXP)... // Can never be true.
if(cX < cXN)... // Can never be true.
What you need to do is:
1) Store the original position of cloudWhite somewhere outside the loop, and store it before the loop begins.
2) Define your bounds relative to the original position of cloudWhite, again before your loop begins. Also define the amount you are going to change the position with each iteration.
3) Start your loop.
4) Increment the current position of cloudWhite on each iteration. Add a little random in here if you want the shape to move in a random manner.
5) Check if the new position of cW is outside your bounds and adjust the direction if it is.
The sample below is crude and jerky but I don't know exactly what effect you're looking for. If you want smoother, longer movements in each direction, consider using the Tween class or a Tween library such as the popular Greensock one, instead of incrementing / decrementing the position manually. There's a useful discussion of this here: http://www.actionscript.org/forums/archive/index.php3/t-163836.html
import flash.display.MovieClip;
import flash.events.Event;
// Set up your variables
var original_x:Number = 100; // Original x
var original_y:Number = 100; // Original y
var x_inc:Number = 5; // X Movement
var y_inc:Number = 5; // Y Movenent
var bounds:Number = 50; // Distance from origin allowed
// Doesn't take into account width of object so is distance to nearest point.
// Create an MC to show the bounds:
var display:MovieClip = addChild(new MovieClip()) as MovieClip;
display.graphics.lineStyle(1, 0x0000FF);
display.graphics.beginFill(0x0000FF, 0.5);
display.graphics.drawRect(0-bounds, 0-bounds, bounds * 2, bounds *2);
display.x = original_x;
display.y = original_y;
addChild(display);
// Create our moving mc:
var mc:MovieClip = addChild(new MovieClip()) as MovieClip;
mc.graphics.beginFill(0xFF0000, 1);
mc.graphics.drawCircle(-10, -10, 20);
// Position it:
mc.x = original_x;
mc.y = original_y;
addChild(mc);
// Loop:
function iterate($e:Event = null):void
{
// Move the mc by a random amount related to x/y inc
mc.x += (Math.random() * (2 * x_inc))/2;
mc.y += (Math.random() * (2 * y_inc))/2;
// If the distance from the origin is greater than bounds:
if((Math.abs(mc.x - original_x)) > bounds)
{
// Reverse the direction of travel:
x_inc == 5 ? x_inc = -5 : x_inc = 5;
}
// Ditto on the y axis:
if((Math.abs(mc.y - original_y)) > bounds)
{
y_inc == 5 ? y_inc = -5 : y_inc = 5;
}
}
// Start the loop:
addEventListener(Event.ENTER_FRAME, iterate);
This should get you started. I'm sure there are any number of other ways to do this with formal trig, but this has the benefit of being very simple, and just an extension of your existing method.