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( function() {
function Particle( x, y ) {
this.x = x;
this.y = y;
this.velocity = 0;
this.accel = 0;
this.friction = 0.15;
}
Particle.prototype.update = function() {
this.velocity += this.accel;
this.velocity *= ( 1 - this.friction );
this.x += this.velocity;
this.accel = 0;
};
Particle.prototype.applyForce = function( force ) {
this.accel += force;
};
Particle.prototype.getRestingPosition = function() {
// get how many ticks until velocity is slow
var restingVelo = 0.07;
var ticks = getBaseLog( 1 - this.friction, restingVelo / Math.abs( this.velocity ) );
// integrate to determine resting position
/*
var x = this.x;
var velo = this.velocity;
while ( ticks > 0 ) {
velo *= 1 - this.friction;
x += velo;
ticks--;
}
*/
// http://mikestoolbox.com/powersum.html
var damping = 1 - this.friction;
var sum = ( Math.pow( damping, ticks + 1 ) - 1 ) / ( damping - 1 );
return this.x + this.velocity * damping * sum;
}
function getBaseLog( a, b ) {
return Math.log( b ) / Math.log( a );
}
window.Particle = Particle;
})();
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