paper.js/src/path/CurveLocation.js

/*
 * Paper.js - The Swiss Army Knife of Vector Graphics Scripting.
 * http://paperjs.org/
 *
 * Copyright (c) 2011 - 2013, Juerg Lehni & Jonathan Puckey
 * http://lehni.org/ & http://jonathanpuckey.com/
 *
 * Distributed under the MIT license. See LICENSE file for details.
 *
 * All rights reserved.
 */

/**
 * @name CurveLocation
 *
 * @class CurveLocation objects describe a location on {@link Curve}
 * objects, as defined by the curve {@link #parameter}, a value between
 * {@code 0} (beginning of the curve) and {@code 1} (end of the curve). If
 * the curve is part of a {@link Path} item, its {@link #index} inside the
 * {@link Path#curves} array is also provided.
 *
 * The class is in use in many places, such as
 * {@link Path#getLocationAt(offset, isParameter)},
 * {@link Path#getLocationOf(point)},
 * {@link Path#getNearestLocation(point),
 * {@link PathItem#getIntersections(path)},
 * etc.
 */
var CurveLocation = this.CurveLocation = Base.extend(/** @lends CurveLocation# */{
	// DOCS: CurveLocation class description: add these back when the  mentioned
	// functioned have been added: {@link Path#split(location)}
	/**
	 * Creates a new CurveLocation object.
	 *
	 * @param {Curve} curve
	 * @param {Number} parameter
	 * @param {Point} point
	 */
	initialize: function(curve, parameter, point, distance) {
		// Define this CurveLocation's unique id.
		this._id = CurveLocation._id = (CurveLocation._id || 0) + 1;
		this._curve = curve;
		// Also store references to segment1 and segment2, in case path
		// splitting / dividing is going to happen, in which case the segments
		// can be used to determine the new curves, see #getCurve(true)
		this._segment1 = curve._segment1;
		this._segment2 = curve._segment2;
		this._parameter = parameter;
		this._point = point;
		this._distance = distance;
	},

	/**
	 * The segment of the curve which is closer to the described location.
	 *
	 * @type Segment
	 * @bean
	 */
	getSegment: function() {
		if (!this._segment) {
			var curve = this.getCurve(),
				parameter = this.getParameter();
			if (parameter == 0) {
				this._segment = curve._segment1;
			} else if (parameter == 1) {
				this._segment = curve._segment2;
			} else if (parameter == null) {
				return null;
			} else {
				// Determine the closest segment by comparing curve lengths
				this._segment = curve.getLength(0, parameter)
					< curve.getLength(parameter, 1)
						? curve._segment1
						: curve._segment2;
			}
		}
		return this._segment;
	},

	/**
	 * The curve by which the location is defined.
	 *
	 * @type Curve
	 * @bean
	 */
	getCurve: function(/* uncached */) {
		if (!this._curve || arguments[0]) {
			// If we're asked to get the curve uncached, access current curve
			// objects through segment1 / segment2. Since path splitting or
			// dividing might have happened in the meantime, try segment1's
			// curve, and see if _point lies on it still, otherwise assume it's
			// the curve before segment2.
			this._curve = this._segment1.getCurve();
			if (this._curve.getParameterOf(this._point) == null)
				this._curve = this._segment2.getPrevious().getCurve();
		}
		return this._curve;
	},

	/**
	 * The path this curve belongs to, if any.
	 *
	 * @type Item
	 * @bean
	 */
	getPath: function() {
		var curve = this.getCurve();
		return curve && curve._path;
	},

	/**
	 * The index of the curve within the {@link Path#curves} list, if the
	 * curve is part of a {@link Path} item.
	 *
	 * @type Index
	 * @bean
	 */
	getIndex: function() {
		var curve = this.getCurve();
		return curve && curve.getIndex();
	},

	/**
	 * The length of the path from its beginning up to the location described
	 * by this object.
	 *
	 * @type Number
	 * @bean
	 */
	getOffset: function() {
		var path = this.getPath();
		return path && path._getOffset(this);
	},

	/**
	 * The length of the curve from its beginning up to the location described
	 * by this object.
	 *
	 * @type Number
	 * @bean
	 */
	getCurveOffset: function() {
		var curve = this.getCurve(),
			parameter = this.getParameter();
		return parameter != null && curve && curve.getLength(0, parameter);
	},

	/**
	 * The curve parameter, as used by various bezier curve calculations. It is
	 * value between {@code 0} (beginning of the curve) and {@code 1} (end of
	 * the curve).
	 *
	 * @type Number
	 * @bean
	 */
	getParameter: function(/* uncached */) {
		if ((this._parameter == null || arguments[0]) && this._point) {
			var curve = this.getCurve(arguments[0] && this._point);
			this._parameter = curve && curve.getParameterOf(this._point);
		}
		return this._parameter;
	},

	/**
	 * The point which is defined by the {@link #curve} and
	 * {@link #parameter}.
	 *
	 * @type Point
	 * @bean
	 */
	getPoint: function() {
		if (!this._point && this._parameter != null) {
			var curve = this.getCurve();
			this._point = curve && curve.getPointAt(this._parameter, true);
		}
		return this._point;
	},

	/**
	 * The tangential vector to the {@link #curve} at the given location.
	 *
	 * @type Point
	 * @bean
	 */
	getTangent: function() {
		var parameter = this.getParameter(),
			curve = this.getCurve();
		return parameter != null && curve && curve.getTangentAt(parameter, true);
	},

	/**
	 * The normal vector to the {@link #curve} at the given location.
	 *
	 * @type Point
	 * @bean
	 */
	getNormal: function() {
		var parameter = this.getParameter(),
			curve = this.getCurve();
		return parameter != null && curve && curve.getNormalAt(parameter, true);
	},

	/**
	 * The distance from the queried point to the returned location.
	 *
	 * @type Number
	 * @bean
	 */
	getDistance: function() {
		return this._distance;
	},

	divide: function() {
		var curve = this.getCurve(true);
		return curve && curve.divide(this.getParameter(true));
	},

	split: function() {
		var curve = this.getCurve(true);
		return curve && curve.split(this.getParameter(true));
	},

	/**
	 * @return {String} A string representation of the curve location.
	 */
	toString: function() {
		var parts = [],
			point = this.getPoint(),
			f = Formatter.instance;
		if (point)
			parts.push('point: ' + point);
		var index = this.getIndex();
		if (index != null)
			parts.push('index: ' + index);
		var parameter = this.getParameter();
		if (parameter != null)
			parts.push('parameter: ' + f.number(parameter));
		if (this._distance != null)
			parts.push('distance: ' + f.number(this._distance));
		return '{ ' + parts.join(', ') + ' }';
	}
});