objectMoon_Step

// first question to ask during every frame:
// how are things going?  Is the computer keeping up?

currentFPS = game_get_speed(gamespeed_fps) ;

// Note that I have to get this value in a Step.
// Merely getting it in a Create tab would have only
// set the initial value, not the moment-to-moment value.
// It probably slows down our our game by a tiny millionth of
// a second per frame -- but it helps us offset those 
// bottlenecks.


// FIRST LUNAR ROTATION, then LUNAR ORBIT
// Calculate rotation and apply to sprite

// how many frames should 1 full rotation (lunar day) get?
framesPerLunarDay = currentFPS * secondsPerLunarDay;

// there are 360 degrees "in" a Lunar Day, so do the math.
moonSpinDelta =  360.0 / framesPerLunarDay;


// NOW APPLY WHAT WE KNOW
// update the stored angle of the moon
moonSpinAngle = moonSpinAngle + moonSpinDelta;

// now make the object instance spin by adjusting sprite rotation
image_angle = moonSpinAngle;





// NOW LUNAR ORBIT
//

// again:  Let's take advantage of the frames per second
// value that GameMaker provides to us.  I've assigned
// it to "currentFPS".  When I take "currentFPS"
// times any length of time, I should get back the
// number of frames that will be shown between now and
// the end of that length of time.  This lets us
// judge how the computer is running, and time things
// out with some precision.

orbitalYearFPS =currentFPS * secondsPerSolarYear;

// how many degrees change per frame?

orbitPixelsPerDegree = orbitalTravelDistanceTotal/360.0;

moonOrbitDelta = orbitPixelsPerDegree / orbitalYearFPS;

moonOrbitAngle = moonOrbitAngle + moonOrbitDelta;


// FINISH UP:  WHERE IS OUR MOON?
// locate the x and y of the moon
// in reference to the planet itself.


// Good old trig functions sine(n) and cosine(n)
// yield a beautiful sine wave, from -1 to 1.
// multiply that number times our orbitalRadiusPixels
// and voila, we have all the points in the circumference
// of a circle.

myX = (sin(moonOrbitAngle) * orbitalRadiusPixels) ;
myY = (cos(moonOrbitAngle) * orbitalRadiusPixels);

// until now, we've been building around 0,0 as the
// defacto center.  So let's add the x,y address of
// our planet in order to shift the whole
// thing in that direction!

x = myX + objectPlanet.x;
y = myY + objectPlanet.y;