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March 20, 2016 03:53
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Draw a slide rule
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| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <script type="text/javascript" src="ruler.js"></script> | |
| <script type="text/javascript"> | |
| window.addEventListener('load', function(){ | |
| var ctx = canvas.getContext('2d'); | |
| draw_button.addEventListener('click', function(){ | |
| ctx.clearRect(0, 0, 1000, 100); | |
| draw(Number(max.value), Number(zoom.value), ctx); | |
| }); | |
| }); | |
| </script> | |
| </head> | |
| <body> | |
| <div> | |
| <canvas id="canvas" width="1000" height="100"></canvas> | |
| </div> | |
| Max: | |
| <input type="text" id="max" /> | |
| Zoom: | |
| <input type="text" id="zoom" /> | |
| <button id="draw_button">Draw</button> | |
| </body> | |
| </html> |
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| const DPI = 101.39; | |
| function cm2px(x){ | |
| return x*DPI/2.54; | |
| } | |
| function draw_line(pos, len, num, ctx){ | |
| ctx.textAlign = 'center'; | |
| ctx.beginPath(); | |
| ctx.moveTo(pos, 0); | |
| ctx.lineTo(pos, len); | |
| ctx.stroke(); | |
| if(num != 0) | |
| ctx.fillText(num, pos, len+12); | |
| } | |
| function draw(max, zoom, ctx){ | |
| var length, num; | |
| for(var i=1; i<=max*10; i++){ | |
| num = 0; | |
| if(i%10 == 0){ | |
| length = 0.7; | |
| num = i/10; | |
| }else if(i%5 == 0){ | |
| length = 0.5; | |
| }else{ | |
| length = 0.4; | |
| } | |
| draw_line(cm2px(zoom*Math.log(0.1*i)), cm2px(length), num, ctx); | |
| } | |
| } |
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