examples/ch04/03-curve-through-point.html

<!doctype html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Curve Through Point</title>
    <link rel="stylesheet" href="../include/style.css">
  </head>
  <body>
    <header>
      Example from <a href="http://amzn.com/1430236655?tag=html5anim-20"><em>Foundation HTML5 Animation with JavaScript</em></a>
    </header>
    <canvas id="canvas" width="400" height="400"></canvas>
    <aside>Move mouse on canvas element.</aside>
    
    <script src="../include/utils.js"></script>
    <script>
    window.onload = function () {
      var canvas = document.getElementById('canvas'),
          context = canvas.getContext('2d'),
          mouse = utils.captureMouse(canvas),
          x0 = 100,
          y0 = 200,
          x2 = 300,
          y2 = 200;
        
      canvas.addEventListener('mousemove', function () {
        context.clearRect(0, 0, canvas.width, canvas.height);

        var x1 = mouse.x * 2 - (x0 + x2) / 2,
            y1 = mouse.y * 2 - (y0 + y2) / 2;

        //curve through mouse
        context.beginPath();
        context.moveTo(x0, y0);
        context.quadraticCurveTo(x1, y1, x2, y2);
        context.stroke();
      }, false);
    };
    </script>
  </body>
</html>