Created
October 18, 2010 13:27
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Code for the Global Composite Operation podcast
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| <!DOCTYPE html> | |
| <html lang="en"> | |
| <head> | |
| <title>Global Composite Operation</title> | |
| <link rel="stylesheet" href="venn.css" type="text/css"> | |
| </head> | |
| <body> | |
| <div id="container"> | |
| <p>Canvas Global Composite Operation</p> | |
| <canvas id="venn" width="1000" height="600"></canvas> | |
| </div> | |
| <script src="venn.js" type="text/javascript" charset="utf-8"></script> | |
| <script type="text/javascript" charset="utf-8"> | |
| window.addEventListener( 'load', function(){ | |
| runVennDemo(); | |
| }, false); | |
| </script> | |
| </body> | |
| </html> |
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| body{ | |
| background: #cacfb4; | |
| } | |
| #container{ | |
| width: 1000px; | |
| height: 100%; | |
| text-align: center; | |
| margin: 0px auto; | |
| } | |
| p{ | |
| font-size: 36pt; | |
| color: #fff; | |
| text-shadow: 1px 1px #000; | |
| padding: 10px; | |
| background-color: rgba(0,0,0,0.4); | |
| margin-top: -15px; | |
| } | |
| p span{ | |
| color: #222; | |
| } |
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| // Draw a circle to context | |
| function drawCircle(ctx, x, y, radius, colour){ | |
| ctx.fillStyle = colour; | |
| ctx.beginPath(); | |
| ctx.arc( x, y, radius, 0, Math.PI * 2, true); | |
| ctx.closePath(); | |
| ctx.fill(); | |
| } | |
| // Run our demo code | |
| function runVennDemo(){ | |
| // Get the 2D context | |
| var ctx = document.getElementById("venn").getContext("2d"); | |
| ctx.globalCompositeOperation = "darker"; | |
| // Draw the "venn diagram" | |
| drawCircle( ctx, 340, 400, 200, "#f00" ); | |
| drawCircle( ctx, 620, 400, 200, "#00f" ); | |
| ctx.globalCompositeOperation = "xor"; // Change the GCO mid-draw | |
| drawCircle( ctx, 475, 200, 200, "#0f0" ); | |
| // Draw some text | |
| ctx.globalAlpha = 0.7; | |
| ctx.globalCompositeOperation = "xor"; | |
| ctx.save(); | |
| ctx.rotate(-20 * Math.PI / 180); | |
| ctx.fillStyle = "#0ff"; | |
| ctx.font = "120pt Helvetica"; | |
| ctx.fillText("HTML5!", 90, 450); | |
| ctx.fillStyle = "#ff0"; | |
| ctx.fillText("HTML5!", 95, 455); | |
| ctx.restore(); | |
| } |
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