<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Hough Lines Example</title>
<link href="js_example_style.css" rel="stylesheet" type="text/css" />
</head>
<body>
<h2>Hough Lines Example</h2>
<p>
<canvas> elements named <b>canvasInput</b> and <b>canvasOutput</b> have been prepared.<br>
Click <b>Try it</b> button to see the result. You can choose another image.<br>
You can change the code in the <textarea> to investigate more.
</p>
<div>
<div class="control"><button id="tryIt" disabled>Try it</button></div>
<textarea class="code" rows="9" cols="100" id="codeEditor" spellcheck="false">
</textarea>
<p class="err" id="errorMessage"></p>
</div>
<div>
<table cellpadding="0" cellspacing="0" width="0" border="0">
<tr>
<td>
<canvas id="canvasInput"></canvas>
</td>
<td>
<canvas id="canvasOutput"></canvas>
</td>
</tr>
<tr>
<td>
<div class="caption">canvasInput <input type="file" id="fileInput" name="file" accept="image/*" /></div>
</td>
<td>
<div class="caption">canvasOutput</div>
</td>
</tr>
</table>
</div>
<script src="utils.js" type="text/javascript"></script>
<script id="codeSnippet" type="text/code-snippet">
let src = cv.imread('canvasInput');
let dst = cv.Mat.zeros(src.rows, src.cols, cv.CV_8UC3);
let lines = new cv.Mat();
cv.cvtColor(src, src, cv.COLOR_RGBA2GRAY, 0);
cv.Canny(src, src, 50, 200, 3);
// You can try more different parameters
cv.HoughLines(src, lines, 1, Math.PI / 180,
30, 0, 0, 0, Math.PI);
// draw lines
for (let i = 0; i < lines.rows; ++i) {
let rho = lines.data32F[i * 2];
let theta = lines.data32F[i * 2 + 1];
let a = Math.cos(theta);
let b = Math.sin(theta);
let x0 = a * rho;
let y0 = b * rho;
let startPoint = {x: x0 - 1000 * b, y: y0 + 1000 * a};
let endPoint = {x: x0 + 1000 * b, y: y0 - 1000 * a};
cv.line(dst, startPoint, endPoint, [255, 0, 0, 255]);
}
cv.imshow('canvasOutput', dst);
src.delete(); dst.delete(); lines.delete();
</script>
<script type="text/javascript">
let utils = new Utils('errorMessage');
utils.loadCode('codeSnippet', 'codeEditor');
utils.loadImageToCanvas('shape.jpg', 'canvasInput');
utils.addFileInputHandler('fileInput', 'canvasInput');
let tryIt = document.getElementById('tryIt');
tryIt.addEventListener('click', () => {
utils.executeCode('codeEditor');
});
utils.loadOpenCv(() => {
tryIt.removeAttribute('disabled');
});
</script>
</body>
</html>