Эффект "стекания" на JS (canvas)

function drip( id ) {
	var bb = new DBUF( id );
	bb.clear();
 
	var ibb = null;
 
	var play = false;
	var rrID = null;
 
	drip.isPlaying = function() {
		return play;
	};
 
	drip.start = function() {
		if ( play ) return;
 
		play = true;
		renderer();
	};
 
	drip.stop = function() {
		if ( !play ) return;
 
		play = false;
		if ( rrID ) {
			bb.cancelRedraw( rrID );
			rrID = null;
		}
	};
 
	var xa = 0, ya = 0;
	drip.setImage = function( url, noAni ) {
		var img = new Image();
		img.onload = function() {
			ibb = new DBUF( "imgbb", this.width, this.height );
			ibb.drawImage( img, 0, 0 );
			xa = Math.floor( ( bb.w - ibb.w ) / 2 );
			ya = Math.floor( ( bb.h - ibb.h ) / 2 );
			if ( xa < 0 ) xa = 0;
			if ( ya < 0 ) ya = 0;
 
			drip.stop();
			if ( noAni ) doDrip();
			else drip.start();
		};
		img.src = url;
	};
 
	var steps = new Array( bb.w );
	var maxStep = 25;
	var minStep = 1;
	var fade = 0.8;
 
	var maxStepH = maxStep * 0.5;
	function countSteps() {
		for ( var i = 0; i < bb.w; i++ ) {
 
			steps[i] = Math.floor( maxStepH - Math.random() * maxStep );
			if ( i > 0 && i % 2 == 0 ) steps[i] = steps[i-1];
 
			if ( steps[i] < minStep ) steps[i] = minStep;
			if ( steps[i] > maxStep ) steps[i] = maxStep;
		}
	}
 
	function doDrip() {
		var x, y, p;
 
		if ( !ibb ) return;
 
		countSteps();
 
		for ( x = 0; x < bb.w; x++ ) {
			var s = steps[x];
			for ( y = bb.h - s - 1; y >= 0; y-- ) {
				p = bb.getPixel( x, y );
				p.r = ( p.r * fade ) & 255;
				p.g = ( p.g * fade ) & 255;
				p.b = ( p.b * fade ) & 255;
				bb.setPixel( x, y + s, p.r, p.g, p.b, 255 );
			}
 
			for ( y = 0; y < s; y++ ) bb.setPixel( x, y, 0, 0, 0, 255 );
		}
 
		for( y = 0; y < ibb.h && y < bb.h; y++ ) {
			for ( x = 0; x < ibb.w && x < bb.w; x++ ) {
				p = ibb.getPixel( x, y );
				if ( p.a > 0 ) {
					bb.mergePixel( x + xa, y + ya, p.r, p.g, p.b, p.a );
				}
			}
		}
 
 
		bb.put();
	}
 
	var frameLength = 150;
	var lastFrame = 0;
	function renderer() {
		rrID = null;
 
		if ( !play ) return;
 
		var now = Date.now();
		if ( now  - lastFrame > frameLength ) {
			lastFrame = now;
			doDrip();
		}
 
		rrID = bb.requestRedraw( renderer );
	}
}