Prototype ¬ Detail

author: mga [+], Submitted: 06.18.02 12p • Last Edit: 12.12.06 9a
Avg. Rating: 5

// moves a MC to (xf,yf) oscillating like a spring
// based on Hooke's Law with damping constant
// k = spring constant
// c = damping constant

MovieClip.prototype.resorte = function (k, c, xf, yf) {
	var yo_mc = this;
	var deltax = 0;
	var vx = 0;
	var ax = 0;
	var deltay = 0;
	var vy = 0;
	var ay = 0;
	yo_mc.onEnterFrame = function () {
		deltax = xf - yo_mc._x;
		ax = -k * deltax;
		vx = c * vx + ax;
		yo_mc._x = yo_mc._x - vx;
		deltay = yf - yo_mc._y;
		ay = -k * deltay;
		vy = c * vy + ay;
		yo_mc._y = yo_mc._y - vy;
		if (xf == yo_mc._x && yf == yo_mc._y && ax < 0.1 && ay < 0.1) {
			delete (yo_mc.onEnterFrame);
		}
	};
};

usage

// this will move yourclip_mc from its current
// position to 500,300 bouncing along the line

yourclip_mc.resorte (.99, .8, 500, 300);

// try different values for k and c
// more FPS give smoother animation

// hope you find it useful
// mga