├── README.md
├── package.json
└── index.js


/README.md:
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 1 | # graham-fast
 2 | ## Usage
 3 | ```javascript
 4 | var grahamScan = require("graham-fast");
 5 | 
 6 | var points = [[0,0],[1,0],[1,1],[0,1],[.5,.5],[-1,-1]];
 7 | 
 8 | var boundaryPoints = grahamScan(points);
 9 | 
10 | console.log(boundaryPoints);
11 | ```
12 | ## License
13 | MIT
14 | 


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/package.json:
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 1 | {
 2 |   "name": "graham-fast",
 3 |   "version": "1.0.0",
 4 |   "description": "Fast implementation of the graham scan algorithm",
 5 |   "main": "index.js",
 6 |   "scripts": {
 7 |     "test": "echo \"Error: no test specified\" && exit 1"
 8 |   },
 9 |   "repository": {
10 |     "type": "git",
11 |     "url": "https://github.com/lovasoa/graham-fast"
12 |   },
13 |   "keywords": [
14 |     "graham",
15 |     "scan",
16 |     "algorithm",
17 |     "convex",
18 |     "hull",
19 |     "envelope",
20 |     "points",
21 |     "stretch",
22 |     "enclose"
23 |   ],
24 |   "author": "Ophir LOJKINE",
25 |   "license": "MIT",
26 |   "bugs": {
27 |     "url": "https://gist.github.com/lovasoa/510ba3f1ece9a623b703"
28 |   },
29 |   "homepage": "https://gist.github.com/lovasoa/510ba3f1ece9a623b703"
30 | }
31 | 


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/index.js:
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 1 | function graham_scan(points) {
 2 |   // The enveloppe is the points themselves
 3 |   if (points.length <= 3) return points;
 4 |   
 5 |   // Find the pivot
 6 |   var pivot = points[0];
 7 |   for (var i=0; i<points.length; i++) {
 8 |     if (points[i][1] < pivot[1] || (points[i][1] === pivot[1] && points[i][0] < pivot[0]))
 9 |       pivot = points[i];
10 |   }
11 | 
12 |   // Attribute an angle to the points
13 |   for (var i=0; i<points.length; i++) {
14 |     points[i]._graham_angle = Math.atan2(points[i][1] - pivot[1], points[i][0] - pivot[0]);
15 |   }
16 |   points.sort(function(a, b){return a._graham_angle === b._graham_angle
17 |                                         ? a[0] - b[0]
18 |                                         : a._graham_angle - b._graham_angle});
19 | 
20 |   // Adding points to the result if they "turn left"
21 |   var result = [points[0]], len=1;
22 |   for(var i=1; i<points.length; i++){
23 |     var a = result[len-2],
24 |         b = result[len-1],
25 |         c = points[i];
26 |     while (
27 |         (len === 1 && b[0] === c[0] && b[1] === c[1]) ||
28 |         (len > 1 && (b[0]-a[0]) * (c[1]-a[1]) <= (b[1]-a[1]) * (c[0]-a[0]))) {
29 |         len--;
30 |         b = a;
31 |         a = result[len-2];
32 |     }
33 |     result[len++] = c;
34 |   }
35 |   result.length = len;
36 |   return result;
37 | }
38 | 
39 | module.exports = graham_scan;
40 | 


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