How To Orbit In AS3

Making some display object orbit around some other display object in ActionScript3.0 is easy.

Here is basic orbit function where all the magic happens:

function orbit(planet:MovieClip, sat:MovieClip, radius:Number, speed:Number):void
{
    var currentDegrees:Number = 0;

    this.addEventListener(Event.ENTER_FRAME, doEveryFrame);

    function doEveryFrame(event:Event):void
    {
        currentDegrees += speed;
        var radians:Number = getRadians(currentDegrees);
        var posX:Number = planet.x + Math.sin(radians) * radius;
        var posY:Number = planet.y + Math.cos(radians) * radius;
        sat.x = posX;
        sat.y = posY;
    }
    
    function getRadians(degrees:Number):Number
    {
        return degrees * Math.PI / 180;
    }    
}

Function parameters:

planet - MovieClip around which another MovieClip is orbiting
sat (satellite) - MovieClip which orbits
radius - distance from satellite to planet
speed - orbit speed (can be positive or negative value)

Orbiting direction depends on speed value. Positive speed value will move satellite in counter-clockwise direction and negative speed value will move satellite in clockwise direction.

Advanced approach can use satellites as new planets, just as in star system you can have star in a center, some planets orbiting around star and than you can add moons around those planets orbiting with different speed and on different distances from planets.

Click on image to download example.



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