maettig/LICENSE.txt

## README.md

      
    Raw
  

              README.md
            
          
    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.

  
## annotated.js
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`
}

## index.js
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}

## LICENSE.txt
            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.

## package.json
{
  "name": "areaPolygon",

  "description": "Calculate the area of non-self-intersecting polygons.",

  "keywords": [
    "area",
    "math",
    "polygon"
  ]
}

## test.html
<!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>
	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`
	}
	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>