/*global define*/
define([
'./Cartesian3',
'./defaultValue',
'./defined',
'./defineProperties',
'./DeveloperError',
'./Spline'
], function(
Cartesian3,
defaultValue,
defined,
defineProperties,
DeveloperError,
Spline) {
'use strict';
/**
* A spline that uses piecewise linear interpolation to create a curve.
*
* @alias LinearSpline
* @constructor
*
* @param {Object} options Object with the following properties:
* @param {Number[]} options.times An array of strictly increasing, unit-less, floating-point times at each point.
* The values are in no way connected to the clock time. They are the parameterization for the curve.
* @param {Cartesian3[]} options.points The array of {@link Cartesian3} control points.
*
* @exception {DeveloperError} points.length must be greater than or equal to 2.
* @exception {DeveloperError} times.length must be equal to points.length.
*
*
* @example
* var times = [ 0.0, 1.5, 3.0, 4.5, 6.0 ];
* var spline = new Cesium.LinearSpline({
* times : times,
* points : [
* new Cesium.Cartesian3(1235398.0, -4810983.0, 4146266.0),
* new Cesium.Cartesian3(1372574.0, -5345182.0, 4606657.0),
* new Cesium.Cartesian3(-757983.0, -5542796.0, 4514323.0),
* new Cesium.Cartesian3(-2821260.0, -5248423.0, 4021290.0),
* new Cesium.Cartesian3(-2539788.0, -4724797.0, 3620093.0)
* ]
* });
*
* var p0 = spline.evaluate(times[0]);
*
* @see HermiteSpline
* @see CatmullRomSpline
* @see QuaternionSpline
*/
function LinearSpline(options) {
options = defaultValue(options, defaultValue.EMPTY_OBJECT);
var points = options.points;
var times = options.times;
//>>includeStart('debug', pragmas.debug);
if (!defined(points) || !defined(times)) {
throw new DeveloperError('points and times are required.');
}
if (points.length < 2) {
throw new DeveloperError('points.length must be greater than or equal to 2.');
}
if (times.length !== points.length) {
throw new DeveloperError('times.length must be equal to points.length.');
}
//>>includeEnd('debug');
this._times = times;
this._points = points;
this._lastTimeIndex = 0;
}
defineProperties(LinearSpline.prototype, {
/**
* An array of times for the control points.
*
* @memberof LinearSpline.prototype
*
* @type {Number[]}
* @readonly
*/
times : {
get : function() {
return this._times;
}
},
/**
* An array of {@link Cartesian3} control points.
*
* @memberof LinearSpline.prototype
*
* @type {Cartesian3[]}
* @readonly
*/
points : {
get : function() {
return this._points;
}
}
});
/**
* Finds an index <code>i</code> in <code>times</code> such that the parameter
* <code>time</code> is in the interval <code>[times[i], times[i + 1]]</code>.
* @function
*
* @param {Number} time The time.
* @returns {Number} The index for the element at the start of the interval.
*
* @exception {DeveloperError} time must be in the range <code>[t<sub>0</sub>, t<sub>n</sub>]</code>, where <code>t<sub>0</sub></code>
* is the first element in the array <code>times</code> and <code>t<sub>n</sub></code> is the last element
* in the array <code>times</code>.
*/
LinearSpline.prototype.findTimeInterval = Spline.prototype.findTimeInterval;
/**
* Evaluates the curve at a given time.
*
* @param {Number} time The time at which to evaluate the curve.
* @param {Cartesian3} [result] The object onto which to store the result.
* @returns {Cartesian3} The modified result parameter or a new instance of the point on the curve at the given time.
*
* @exception {DeveloperError} time must be in the range <code>[t<sub>0</sub>, t<sub>n</sub>]</code>, where <code>t<sub>0</sub></code>
* is the first element in the array <code>times</code> and <code>t<sub>n</sub></code> is the last element
* in the array <code>times</code>.
*/
LinearSpline.prototype.evaluate = function(time, result) {
var points = this.points;
var times = this.times;
var i = this._lastTimeIndex = this.findTimeInterval(time, this._lastTimeIndex);
var u = (time - times[i]) / (times[i + 1] - times[i]);
if (!defined(result)) {
result = new Cartesian3();
}
return Cartesian3.lerp(points[i], points[i + 1], u, result);
};
return LinearSpline;
});