tatocaster/index.html

## index.html
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <title>Rotating Arc on canvas</title>
</head>
<body>
  <canvas id="canvas" width="400" height="150"></canvas>
  <script type="text/javascript" src="script.js"></script>
</body>
</html>

## script.js

/**
 * @author tatocaster <kutaliatato@gmail.com>
*/
(function(window){
    var canvas        = document.getElementById('canvas');
    var context       = canvas.getContext('2d');
    canvas.width  = window.innerWidth;
    canvas.height = window.innerHeight;
    context.strokeStyle = "red";
    context.lineWidth = "5";


    // ცენტრის მიმართ კუთხის გამოსათვლელად
    var canvasOffsetX = canvas.width/2;
    var canvasOffsetY = canvas.height/2;
    var radiusX       = canvas.width/2;
    var radiusY       = canvas.height/2;
    var radius        = 50;

    function drawArc(mouseMoveEvent){
    var e = mouseMoveEvent;

    context.clearRect(0, 0, canvas.width, canvas.height);

    // კუთხის გამოთვლა რადიანებში.
    var rotateAngle = Math.atan2(parseInt(canvasOffsetX - e.clientX), parseInt(e.clientY - canvasOffsetY));


    context.beginPath();
    context.arc(radiusX, radiusY, radius, rotateAngle, rotateAngle + Math.PI);
    context.stroke();
    }

    canvas.onmousemove=function(e){drawArc(e);};
})(window);
	<!DOCTYPE html>
	<html>
	<head>
	<meta charset="utf-8">
	<title>Rotating Arc on canvas</title>
	</head>
	<body>
	<canvas id="canvas" width="400" height="150"></canvas>
	<script type="text/javascript" src="script.js"></script>
	</body>
	</html>

	/**
	* @author tatocaster <kutaliatato@gmail.com>
	*/
	(function(window){
	var canvas = document.getElementById('canvas');
	var context = canvas.getContext('2d');
	canvas.width = window.innerWidth;
	canvas.height = window.innerHeight;
	context.strokeStyle = "red";
	context.lineWidth = "5";



	// ცენტრის მიმართ კუთხის გამოსათვლელად
	var canvasOffsetX = canvas.width/2;
	var canvasOffsetY = canvas.height/2;
	var radiusX = canvas.width/2;
	var radiusY = canvas.height/2;
	var radius = 50;

	function drawArc(mouseMoveEvent){
	var e = mouseMoveEvent;

	context.clearRect(0, 0, canvas.width, canvas.height);

	// კუთხის გამოთვლა რადიანებში.
	var rotateAngle = Math.atan2(parseInt(canvasOffsetX - e.clientX), parseInt(e.clientY - canvasOffsetY));


	context.beginPath();
	context.arc(radiusX, radiusY, radius, rotateAngle, rotateAngle + Math.PI);
	context.stroke();
	}

	canvas.onmousemove=function(e){drawArc(e);};
	})(window);