leaflet/src/layer/vector/Polygon.js

JavaScript library for mobile-friendly interactive maps

/*
 * @class Polygon
 * @aka L.Polygon
 * @inherits Polyline
 *
 * A class for drawing polygon overlays on a map. Extends `Polyline`.
 *
 * Note that points you pass when creating a polygon shouldn't have an additional last point equal to the first one — it's better to filter out such points.
 *
 *
 * @example
 *
 * ```js
 * // create a red polygon from an array of LatLng points
 * var latlngs = [[37, -109.05],[41, -109.03],[41, -102.05],[37, -102.04]];
 *
 * var polygon = L.polygon(latlngs, {color: 'red'}).addTo(map);
 *
 * // zoom the map to the polygon
 * map.fitBounds(polygon.getBounds());
 * ```
 *
 * You can also pass an array of arrays of latlngs, with the first array representing the outer shape and the other arrays representing holes in the outer shape:
 *
 * ```js
 * var latlngs = [
 *   [[37, -109.05],[41, -109.03],[41, -102.05],[37, -102.04]], // outer ring
 *   [[37.29, -108.58],[40.71, -108.58],[40.71, -102.50],[37.29, -102.50]] // hole
 * ];
 * ```
 *
 * Additionally, you can pass a multi-dimensional array to represent a MultiPolygon shape.
 *
 * ```js
 * var latlngs = [
 *   [ // first polygon
 *     [[37, -109.05],[41, -109.03],[41, -102.05],[37, -102.04]], // outer ring
 *     [[37.29, -108.58],[40.71, -108.58],[40.71, -102.50],[37.29, -102.50]] // hole
 *   ],
 *   [ // second polygon
 *     [[41, -111.03],[45, -111.04],[45, -104.05],[41, -104.05]]
 *   ]
 * ];
 * ```
 */

L.Polygon = L.Polyline.extend({

	options: {
		fill: true
	},

	isEmpty: function () {
		return !this._latlngs.length || !this._latlngs[0].length;
	},

	getCenter: function () {
		// throws error when not yet added to map as this center calculation requires projected coordinates
		if (!this._map) {
			throw new Error('Must add layer to map before using getCenter()');
		}

		var i, j, p1, p2, f, area, x, y, center,
		    points = this._rings[0],
		    len = points.length;

		if (!len) { return null; }

		// polygon centroid algorithm; only uses the first ring if there are multiple

		area = x = y = 0;

		for (i = 0, j = len - 1; i < len; j = i++) {
			p1 = points[i];
			p2 = points[j];

			f = p1.y * p2.x - p2.y * p1.x;
			x += (p1.x + p2.x) * f;
			y += (p1.y + p2.y) * f;
			area += f * 3;
		}

		if (area === 0) {
			// Polygon is so small that all points are on same pixel.
			center = points[0];
		} else {
			center = [x / area, y / area];
		}
		return this._map.layerPointToLatLng(center);
	},

	_convertLatLngs: function (latlngs) {
		var result = L.Polyline.prototype._convertLatLngs.call(this, latlngs),
		    len = result.length;

		// remove last point if it equals first one
		if (len >= 2 && result[0] instanceof L.LatLng && result[0].equals(result[len - 1])) {
			result.pop();
		}
		return result;
	},

	_setLatLngs: function (latlngs) {
		L.Polyline.prototype._setLatLngs.call(this, latlngs);
		if (L.Polyline._flat(this._latlngs)) {
			this._latlngs = [this._latlngs];
		}
	},

	_defaultShape: function () {
		return L.Polyline._flat(this._latlngs[0]) ? this._latlngs[0] : this._latlngs[0][0];
	},

	_clipPoints: function () {
		// polygons need a different clipping algorithm so we redefine that

		var bounds = this._renderer._bounds,
		    w = this.options.weight,
		    p = new L.Point(w, w);

		// increase clip padding by stroke width to avoid stroke on clip edges
		bounds = new L.Bounds(bounds.min.subtract(p), bounds.max.add(p));

		this._parts = [];
		if (!this._pxBounds || !this._pxBounds.intersects(bounds)) {
			return;
		}

		if (this.options.noClip) {
			this._parts = this._rings;
			return;
		}

		for (var i = 0, len = this._rings.length, clipped; i < len; i++) {
			clipped = L.PolyUtil.clipPolygon(this._rings[i], bounds, true);
			if (clipped.length) {
				this._parts.push(clipped);
			}
		}
	},

	_updatePath: function () {
		this._renderer._updatePoly(this, true);
	}
});


// @factory L.polygon(latlngs: LatLng[], options?: Polyline options)
L.polygon = function (latlngs, options) {
	return new L.Polygon(latlngs, options);
};