A tiny JavaScript function (104 103 bytes thanks to @tsaniel) calculates the area of a simple, non-self-intersecting polygon. Please note that the calculation is wrong if the polygon is self-intersecting.
Click here to see it in action. Reload the page for an other random example.
Inspired by areaTriangle by @neizod.
| function(a) //array of points, e.g. `[[1, 2], [3, 4]]` | |
| { | |
| for ( //for all points in the array | |
| var b = 0, //initially, the area is zero | |
| c = a.length, //start from the last point in the array | |
| d; //declare `d` | |
| c; //continue as long as `c` is not zero | |
| b += (d[0] - a[--c][0]) //this calculates the sum of a series of triangles | |
| * (d[1] + a[ c][1]) //from the previous point `d` to the current one | |
| / 2) //note that this is executed after the following line | |
| d = a[d ? c : 0]; //`d` becomes a shortcut for `a[c % a.length]` | |
| return b < 0 ? -b : b //short replacement for `Math.abs` | |
| } |
| function(a){for(var b=0,c=a.length,d;c;b+=(d[0]-a[--c][0])*(d[1]+a[c][1])/2)d=a[d?c:0];return b<0?-b:b} |
| DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE | |
| Version 2, December 2004 | |
| Copyright (C) 2012 Thiemo Mättig <http://maettig.com> | |
| Everyone is permitted to copy and distribute verbatim or modified | |
| copies of this license document, and changing it is allowed as long | |
| as the name is changed. | |
| DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE | |
| TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION | |
| 0. You just DO WHAT THE FUCK YOU WANT TO. |
| { | |
| "name": "areaPolygon", | |
| "description": "Calculate the area of non-self-intersecting polygons.", | |
| "keywords": [ | |
| "area", | |
| "math", | |
| "polygon" | |
| ] | |
| } |
| <!DOCTYPE html> | |
| <style type="text/css"> | |
| svg, pre { background: #DDE; border: 2px solid #66B; font-family: Consolas, monospace; padding: .3em; } | |
| svg { width: 200px; } | |
| </style> | |
| <pre>This page requires JavaScript.</pre> | |
| <svg id="s" viewBox="-1 -1 2 2" xmlns="http://www.w3.org/2000/svg"> | |
| <defs><marker id="m" markerHeight="5" markerWidth="5" viewBox="-1 -1 2 2"><circle r="1" /></marker></defs> | |
| <path d="M0 0h1v1z" fill="#E66" fill-rule="evenodd" marker-end="url(#m)" marker-mid="url(#m)" stroke="#600" stroke-width=".01" /> | |
| <path d="M0 -1v2M-1 0h2" stroke="#009" stroke-width=".01" /> | |
| </svg> | |
| <script type="text/javascript"> | |
| // 103 bytes | |
| var areaPolygon = function(a) //array of points, e.g. `[[1, 2], [3, 4]]` | |
| { | |
| for ( //for all points in the array | |
| var b = 0, //initially, the area is zero | |
| c = a.length, //start from the last point in the array | |
| d; //declare `d` | |
| c; //continue as long as `c` is not zero | |
| b += (d[0] - a[--c][0]) //this calculates the sum of a series of triangles | |
| * (d[1] + a[ c][1]) //from the previous point `d` to the current one | |
| / 2) //note that this is executed after the following line | |
| d = a[d ? c : 0]; //`d` becomes a shortcut for `a[c % a.length]` | |
| return b < 0 ? -b : b //short replacement for `Math.abs` | |
| } | |
| var p = new Array(3 + Math.random() * 3 | 0); | |
| var d = ''; | |
| for (var i = p.length; i--; ) | |
| { | |
| p[i] = [(Math.random() * 200 - 100 | 0) / 100, (Math.random() * 200 - 100 | 0) / 100]; | |
| d += (d ? 'L' : 'M') + p[i][0] + ' ' + p[i][1]; | |
| } | |
| document.getElementsByTagName('PRE')[0].firstChild.data = 'area([[' + p.join('],\n [') + ']]) = ' + areaPolygon(p); | |
| // Workaround for Firefox since getElementsByTagName does not work with inline SVG. | |
| var n = document.getElementById('s').firstChild; | |
| while (n && (n.nodeType != 1 || n.nodeName.toLowerCase() != 'path')) n = n.nextSibling; | |
| n.setAttribute('d', d + 'z'); | |
| </script> |
That's impossi... oh, wait, it's not. This is funny because I had so many iterations while golfing this down (they are all included here) but the /2 never moved.
Save 1 byte.