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March 7, 2015 07:40
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How to distort an actual image to create flag waving in the wind effect using html5 canvas
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| <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> | |
| <html><head> | |
| <title>HTML Canvas Flag Wave</title> | |
| <style type="text/css" media="screen"> | |
| body { background:#eee } | |
| #flag { position:absolute; top:50%; left:50% } | |
| </style> | |
| <script type="text/javascript"> | |
| var h = new Image; | |
| h.onload = function(){ | |
| var flag = document.getElementById('flag'); | |
| var amp = 20; | |
| flag.width = h.width; | |
| flag.height = h.height + amp*2; | |
| flag.getContext('2d').drawImage(h,0,amp,h.width,h.height); | |
| flag.style.marginLeft = -(flag.width/2)+'px'; | |
| flag.style.marginTop = -(flag.height/2)+'px'; | |
| var timer = waveFlag( flag, h.width/10, amp ); | |
| }; | |
| h.src = 'gkhead.jpg'; | |
| function waveFlag( canvas, wavelength, amplitude, period, shading, squeeze ){ | |
| if (!squeeze) squeeze = 0; | |
| if (!shading) shading = 100; | |
| if (!period) period = 200; | |
| if (!amplitude) amplitude = 10; | |
| if (!wavelength) wavelength = canvas.width/10; | |
| var fps = 30; | |
| var ctx = canvas.getContext('2d'); | |
| var w = canvas.width, h = canvas.height; | |
| var od = ctx.getImageData(0,0,w,h).data; | |
| // var ct = 0, st=new Date; | |
| return setInterval(function(){ | |
| var id = ctx.getImageData(0,0,w,h); | |
| var d = id.data; | |
| var now = (new Date)/period; | |
| for (var y=0;y<h;++y){ | |
| var lastO=0,shade=0; | |
| var sq = (y-h/2)*squeeze; | |
| for (var x=0;x<w;++x){ | |
| var px = (y*w + x)*4; | |
| var pct = x/w; | |
| var o = Math.sin(x/wavelength-now)*amplitude*pct; | |
| var y2 = y + (o+sq*pct)<<0; | |
| var opx = (y2*w + x)*4; | |
| shade = (o-lastO)*shading; | |
| d[px ] = od[opx ]+shade; | |
| d[px+1] = od[opx+1]+shade; | |
| d[px+2] = od[opx+2]+shade; | |
| d[px+3] = od[opx+3]; | |
| lastO = o; | |
| } | |
| } | |
| ctx.putImageData(id,0,0); | |
| // if ((++ct)%100 == 0) console.log( 1000 * ct / (new Date - st)); | |
| },1000/fps); | |
| } | |
| </script> | |
| </head><body> | |
| <canvas id="flag"></canvas> | |
| </body></html> | |
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