src/plugins/leaflet-draw/ext/Polyline.Intersect.js

/**
 * @class L.Polyline
 * @aka Polyline
 */
L.Polyline.include({

	// @method intersects(): boolean
	// Check to see if this polyline has any linesegments that intersect.
	// NOTE: does not support detecting intersection for degenerate cases.
	intersects: function () {
		var points = this._getProjectedPoints(),
			len = points ? points.length : 0,
			i, p, p1;

		if (this._tooFewPointsForIntersection()) {
			return false;
		}

		for (i = len - 1; i >= 3; i--) {
			p = points[i - 1];
			p1 = points[i];


			if (this._lineSegmentsIntersectsRange(p, p1, i - 2)) {
				return true;
			}
		}

		return false;
	},

	// @method newLatLngIntersects(): boolean
	// Check for intersection if new latlng was added to this polyline.
	// NOTE: does not support detecting intersection for degenerate cases.
	newLatLngIntersects: function (latlng, skipFirst) {
		// Cannot check a polyline for intersecting lats/lngs when not added to the map
		if (!this._map) {
			return false;
		}

		return this.newPointIntersects(this._map.latLngToLayerPoint(latlng), skipFirst);
	},

	// @method newPointIntersects(): boolean
	// Check for intersection if new point was added to this polyline.
	// newPoint must be a layer point.
	// NOTE: does not support detecting intersection for degenerate cases.
	newPointIntersects: function (newPoint, skipFirst) {
		var points = this._getProjectedPoints(),
			len = points ? points.length : 0,
			lastPoint = points ? points[len - 1] : null,
			// The previous previous line segment. Previous line segment doesn't need testing.
			maxIndex = len - 2;

		if (this._tooFewPointsForIntersection(1)) {
			return false;
		}

		return this._lineSegmentsIntersectsRange(lastPoint, newPoint, maxIndex, skipFirst ? 1 : 0);
	},

	// Polylines with 2 sides can only intersect in cases where points are collinear (we don't support detecting these).
	// Cannot have intersection when < 3 line segments (< 4 points)
	_tooFewPointsForIntersection: function (extraPoints) {
		var points = this._getProjectedPoints(),
			len = points ? points.length : 0;
		// Increment length by extraPoints if present
		len += extraPoints || 0;

		return !points || len <= 3;
	},

	// Checks a line segment intersections with any line segments before its predecessor.
	// Don't need to check the predecessor as will never intersect.
	_lineSegmentsIntersectsRange: function (p, p1, maxIndex, minIndex) {
		var points = this._getProjectedPoints(),
			p2, p3;

		minIndex = minIndex || 0;

		// Check all previous line segments (beside the immediately previous) for intersections
		for (var j = maxIndex; j > minIndex; j--) {
			p2 = points[j - 1];
			p3 = points[j];

			if (L.LineUtil.segmentsIntersect(p, p1, p2, p3)) {
				return true;
			}
		}

		return false;
	},

	_getProjectedPoints: function () {
		if (!this._defaultShape) {
			return this._originalPoints;
		}
		var points = [],
			_shape = this._defaultShape();

		for (var i = 0; i < _shape.length; i++) {
			points.push(this._map.latLngToLayerPoint(_shape[i]));
		}
		return points;
	}
});