cesiumDemo/Source/Core/LinearSpline.js

import Cartesian3 from './Cartesian3.js';
import defaultValue from './defaultValue.js';
import defined from './defined.js';
import defineProperties from './defineProperties.js';
import DeveloperError from './DeveloperError.js';
import Spline from './Spline.js';

    /**
     * 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
     * @see WeightSpline
     */
    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;

    /**
     * Wraps the given time to the period covered by the spline.
     * @function
     *
     * @param {Number} time The time.
     * @return {Number} The time, wrapped around to the updated animation.
     */
    LinearSpline.prototype.wrapTime = Spline.prototype.wrapTime;

    /**
     * Clamps the given time to the period covered by the spline.
     * @function
     *
     * @param {Number} time The time.
     * @return {Number} The time, clamped to the animation period.
     */
    LinearSpline.prototype.clampTime = Spline.prototype.clampTime;

    /**
     * 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);
    };
export default LinearSpline;