Created
October 14, 2012 13:09
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HTML5 Canvas Drawing of Pentagram, Heptagram, ...
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <meta charset="UTF-8"> | |
| <title>n-tagram</title> | |
| <script src="http://code.jquery.com/jquery-1.8.2.min.js"></script> | |
| </head> | |
| <body> | |
| <label for="pointsSpinner">Points: </label> | |
| <input id="pointsSpinner" type="number" value="5"/> | |
| <label for="stepSpinner">Step: </label> | |
| <input id="stepSpinner" type="number" value="2"/> | |
| <canvas id="thecanvas" width="600" height="600"></canvas> | |
| <script type="text/javascript"> | |
| var $cvs = null; | |
| var $ctx = null; | |
| var $R = null; | |
| var update_context = (function() { | |
| $cvs = $("#thecanvas")[0]; | |
| $ctx = $cvs.getContext("2d"); | |
| var width = $cvs.width; | |
| var height = $cvs.height; | |
| $R = (width < height ? width : height) / 2; | |
| }); | |
| var clear = (function() { | |
| update_context(); | |
| $ctx.fillStyle = "rgb(255,255,255)"; | |
| $ctx.fillRect(0, 0, $cvs.width, $cvs.height); | |
| }); | |
| var ntagram = (function(points, step, color) { | |
| update_context(); | |
| $ctx.strokeStyle = color; | |
| $ctx.lineWidth = 5; | |
| $ctx.lineCap = "round"; | |
| for(var i = 0; i < points; ++i) { | |
| var t = 2 * Math.PI * (i * step) / points; | |
| var x = $R + $R * Math.cos(t); | |
| var y = $R + $R * Math.sin(t); | |
| $ctx.beginPath(); | |
| $ctx.moveTo(x, y); | |
| t = 2 * Math.PI * ((i + 1) * step) / points; | |
| x = $R + $R * Math.cos(t); | |
| y = $R + $R * Math.sin(t); | |
| $ctx.lineTo(x, y); | |
| $ctx.stroke(); | |
| } | |
| }); | |
| </script> | |
| <script type="text/javascript"> | |
| $(function() { | |
| // set-up event handlers | |
| var pointsSpinner = $("#pointsSpinner")[0]; | |
| var stepSpinner = $("#stepSpinner")[0]; | |
| var redraw = (function() { | |
| clear(); | |
| ntagram(pointsSpinner.value, 1, "red"); | |
| ntagram(pointsSpinner.value, stepSpinner.value, "blue"); | |
| }); | |
| pointsSpinner.addEventListener("input", redraw, false); | |
| stepSpinner.addEventListener("input", redraw, false); | |
| // fire initial drawing | |
| redraw(); | |
| }); | |
| </script> | |
| </body> | |
| </html> |
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Chrome/chromium (or any HTML5-supporting browsers) recommend, because the numbers of "Points" and "Step" can be modified with cursor keys.