canvas_w_96px_square.html
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<!DOCTYPE html>
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<html lang="en"> |
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<head>
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<meta charset="utf-8" /> |
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<title>Canvas Drawing Example</title> |
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<script>
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var canvas;
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var ctx;
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var fontCanvas;
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var fontCtx;
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function textHeight(font, text, width)
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{
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var height = 128;
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fontCtx.save();
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fontCanvas.setAttribute('height', height);
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fontCanvas.setAttribute('width', width);
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fontCtx.fillStyle = 'black';
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fontCtx.fillRect(0, 0, width, height);
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fontCtx.textBaseline = 'top';
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fontCtx.fillStyle = 'white';
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fontCtx.font = font;
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fontCtx.fillText(text, 0, 0);
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var pixels = fontCtx.getImageData(0, 0, width, height).data;
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// row numbers where we first find letter end where it ends
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var beg = -1;
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var end = -1;
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for (var row = 0; row < height; row++)
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{
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for (var col = 0; col < width; col++)
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{
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var index = (row * width + col) * 4;
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// if pixel is not white (background color)
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if (pixels[index] === 0)
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{
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// we haven't met white (font color) pixel
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// on the row and the letters was detected
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if (col === (width - 1) && beg !== -1)
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{
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end = row;
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row = height;
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break;
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}
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}
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else
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{
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// we find top of letter
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if (beg === -1)
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{
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beg = row;
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}
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// ..letters body
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break;
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}
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}
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}
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fontCtx.restore();
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return end - beg;
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}
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window.onload=function()
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{
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canvas = document.getElementById("bogus");
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ctx = canvas.getContext('2d');
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canvas.top = 150;
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canvas.left = 150;
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canvas.width = 700;
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canvas.height = 300;
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ctx.lineWidth = 1;
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ctx.imageSmoothingEnabled = false;
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ctx.translate(0.5, 0.5);
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ctx.fillRect(10, 10, 96, 96);
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var font = "96px sans-serif";
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var text = "WITM";
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ctx.font = font;
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ctx.textBaseline = "top";
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ctx.fillText(text, 130, 10);
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fontCanvas = document.createElement('canvas');
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fontCtx = fontCanvas.getContext('2d');
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var width = ctx.measureText(text).width;
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var ht = textHeight(font, text, width);
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ctx.font = "16px sans-serif";
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ctx.fillText("textHeight = " + ht + "px", 130 + 30 + width, 53);
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};
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</script>
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</head>
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<body>
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<canvas id="bogus" style="position:'absolute';">No HTML5 support in your browser!</canvas> |
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</body>
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</html>
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