function draw_roulette(ctx, w, h, datalist){
	var radius = h / 2 - 5;
	var center = new Array(w / 2, h / 2);
	var init = 0;
	var total = datalist.reduce((acc, value) => acc + value, init);
	var lastend = 0;
	var offset = Math.PI / 2;
	for (i=0; i < datalist.length; i++){
		var part = datalist[i];

		ctx.beginPath();
		ctx.fillStyle = colist[i];
		ctx.moveTo(center[0], center[1]);
		var arcsector = Math.PI * (2 * part / total);
		ctx.arc(center[0], center[1], radius, lastend - offset, lastend + arcsector - offset, false);
		ctx.lineTo(center[0], center[1]);
		ctx.fill();
		ctx.closePath();		
		lastend += arcsector;	
	}
}