Draw Golden Rectangle Using Javascript

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I’m reading a book on the history and prevalence of the golden ratio called The Golden Ratio by Mario Livio. It inspired me to write a javascript function that dynamically draws the golden rectangle on your computer screen. Mathematicians call the center of the rectangle the “eye of god.” Here’s the live page, and here’s the source:

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<html>
  <!--
  Copyright (C) 2012 David Xia

  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:

  The above copyright notice and this permission notice shall be included in
  all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  -->
  <head>
    <title>Golden Ratio Fun</title>
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js"></script>

    <script type="text/javascript">
        function loadCanvas(){
            // get available screen size
            var availWidth = $(window).width() - 20;
            var availHeight = $(window).height() - 20;

            // instantiate golden ratio constant
            var PHI = (1+ Math.sqrt(5))/2;

            // resize canvas based on golden ratio
            if(availWidth/availHeight > PHI){
                availWidth = availHeight * PHI;
            } else if(availWidth/availHeight < PHI){
                availHeight = availWidth/PHI;
            }

            // add canvas HTML tag to body
            var canvasTag = '<canvas id="canvas" width="'+availWidth+'" height="'+availHeight+'"></canvas>';
            $('body').html(canvasTag);

            // prepare to draw
            var canvas = $('canvas').get(0);
            if(canvas.getContext){
                var ctx = canvas.getContext('2d');
            }

            // draw first inner golden rectangle
            var x1 = availWidth/PHI;
            ctx.beginPath();
            ctx.moveTo(x1, 0);
            ctx.lineTo(x1, availHeight);
            ctx.stroke();

            // draw arc
            ctx.beginPath();
            ctx.moveTo(x1, availHeight);
            ctx.arc(x1, availHeight, x1, Math.PI, (3/2*Math.PI));
            ctx.stroke();

            // draw second inner rectangle
            var y1 = availHeight/PHI;
            ctx.beginPath();
            ctx.moveTo(x1, y1);
            ctx.lineTo(availWidth, y1);
            ctx.stroke();

            // draw arc
            ctx.beginPath();
            ctx.moveTo(x1, y1);
            ctx.arc(x1, y1, y1, (3/2*Math.PI), 0);
            ctx.stroke();

            // draw 3rd
            var x2 = availWidth - (availWidth-x1)/PHI;
            ctx.beginPath();
            ctx.moveTo(x2, y1);
            ctx.lineTo(x2, availHeight);
            ctx.stroke();

            // draw arc
            ctx.beginPath();
            ctx.moveTo(availWidth, y1);
            ctx.arc(x2, y1, (availHeight-y1), 0, (1/2*Math.PI));
            ctx.stroke();

            // draw 4th
            var y2 = availHeight - (availHeight-y1)/PHI;
            ctx.beginPath();
            ctx.moveTo(x1, y2);
            ctx.lineTo(x2, y2);
            ctx.stroke();

            // draw arc
            ctx.beginPath();
            ctx.moveTo(x2, y2);
            ctx.arc(x2, y2, (availHeight-y2), (1/2*Math.PI), Math.PI);
            ctx.stroke();

            // draw 5th
            var x3 = x1 + (x2-x1)/PHI;
            ctx.beginPath();
            ctx.moveTo(x3, y1);
            ctx.lineTo(x3, y2);
            ctx.stroke();

            // draw arc
            ctx.beginPath();
            ctx.moveTo(x3, y2);
            ctx.arc(x3, y2, (x3-x1), Math.PI, (3/2*Math.PI));
            ctx.stroke();

            // draw 6th
            var y3 = y1 + (y2-y1)/PHI;
            ctx.beginPath();
            ctx.moveTo(x3, y3);
            ctx.lineTo(x2, y3);
            ctx.stroke();

            // draw arc
            ctx.beginPath();
            ctx.moveTo(x3, y3);
            ctx.arc(x3, y3, (x2-x3), (3/2*Math.PI), 0);
            ctx.stroke();

            // draw 7th
            var x4 = x2 - (x2-x3)/PHI;
            ctx.beginPath();
            ctx.moveTo(x4, y3);
            ctx.lineTo(x4, y2);
            ctx.stroke();

            // draw arc
            ctx.beginPath();
            ctx.moveTo(x4, y3);
            ctx.arc(x4, y3, (x2-x4), 0, (1/2*Math.PI));
            ctx.stroke();

            // draw 8th
            var y4 = y2 - (y2-y3)/PHI;
            ctx.beginPath();
            ctx.moveTo(x3, y4);
            ctx.lineTo(x4, y4);
            ctx.stroke();

            // draw arc
            ctx.beginPath();
            ctx.moveTo(x4, y4);
            ctx.arc(x4, y4, (x4-x3), (1/2*Math.PI), Math.PI);
            ctx.stroke();

            // draw 9th
            var x5 = x3 + (x4-x3)/PHI;
            ctx.beginPath();
            ctx.moveTo(x5, y3);
            ctx.lineTo(x5, y4);
            ctx.stroke();

            // draw arc
            ctx.beginPath();
            ctx.moveTo(x5, y4);
            ctx.arc(x5, y4, (x5-x3), Math.PI, (3/2*Math.PI));
            ctx.stroke();

            // draw 10th
            var y5 = y3 + (y4-y3)/PHI;
            ctx.beginPath();
            ctx.moveTo(x4, y5);
            ctx.lineTo(x5, y5);
            ctx.stroke();

            // draw arc
            ctx.beginPath();
            ctx.moveTo(x5, y5);
            ctx.arc(x5, y5, (x4-x5), (3/2*Math.PI), 0);
            ctx.stroke();

            // draw 11th
            var x6 = x4 - (x4-x5)/PHI;
            ctx.beginPath();
            ctx.moveTo(x6, y4);
            ctx.lineTo(x6, y5);
            ctx.stroke();

            // draw arc
            ctx.beginPath();
            ctx.moveTo(x6, y5);
            ctx.arc(x6, y5, (x4-x6), 0, (1/2*Math.PI));
            ctx.stroke();

            // draw 12th
            var y6 = y4 - (y4-y5)/PHI;
            ctx.beginPath();
            ctx.moveTo(x5, y6);
            ctx.lineTo(x6, y6);
            ctx.stroke();

            // draw arc
            ctx.beginPath();
            ctx.moveTo(x6, y6);
            ctx.arc(x6, y6, (x6-x5), (1/2*Math.PI), Math.PI);
            ctx.stroke();

        }

        // redraws golden rectangles if window is resized
        $(window).resize(function() {
            loadCanvas();
        });
    </script>
    <style type="text/css">
      canvas { border: 2px solid black; }
    </style>
</head>


<body onload="loadCanvas()">
</body>
</html>

golden rectangle

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