Source/Widgets/CesiumWidget/CesiumWidget.js

/*global define*/
define([
        '../../Core/buildModuleUrl',
        '../../Core/Cartesian2',
        '../../Core/Cartesian3',
        '../../Core/Clock',
        '../../Core/DefaultProxy',
        '../../Core/defaultValue',
        '../../Core/defineProperties',
        '../../Core/destroyObject',
        '../../Core/DeveloperError',
        '../../Core/Ellipsoid',
        '../../Core/FeatureDetection',
        '../../Core/requestAnimationFrame',
        '../../Core/ScreenSpaceEventHandler',
        '../../Scene/BingMapsImageryProvider',
        '../../Scene/CentralBody',
        '../../Scene/Credit',
        '../../Scene/Scene',
        '../../Scene/SceneMode',
        '../../Scene/SceneTransitioner',
        '../../Scene/SkyAtmosphere',
        '../../Scene/SkyBox',
        '../../Scene/Sun',
        '../getElement'
    ], function(
        buildModuleUrl,
        Cartesian2,
        Cartesian3,
        Clock,
        DefaultProxy,
        defaultValue,
        defineProperties,
        destroyObject,
        DeveloperError,
        Ellipsoid,
        FeatureDetection,
        requestAnimationFrame,
        ScreenSpaceEventHandler,
        BingMapsImageryProvider,
        CentralBody,
        Credit,
        Scene,
        SceneMode,
        SceneTransitioner,
        SkyAtmosphere,
        SkyBox,
        Sun,
        getElement) {
    "use strict";

    function getDefaultSkyBoxUrl(suffix) {
        return buildModuleUrl('Assets/Textures/SkyBox/tycho2t3_80_' + suffix + '.jpg');
    }

    function startRenderLoop(widget) {
        widget._renderLoopRunning = true;

        function render() {
            try {
                if (widget._useDefaultRenderLoop) {
                    widget.resize();
                    widget.render();
                    requestAnimationFrame(render);
                } else {
                    widget._renderLoopRunning = false;
                }
            } catch (e) {
                widget._useDefaultRenderLoop = false;
                widget._renderLoopRunning = false;
                widget.onRenderLoopError.raiseEvent(widget, e);
            }
        }

        requestAnimationFrame(render);
    }

    var cesiumLogoData = 'data:image/png;base64,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';

    /**
     * A widget containing a Cesium scene.
     *
     * @alias CesiumWidget
     * @constructor
     *
     * @param {Element|String} container The DOM element or ID that will contain the widget.
     * @param {Object} [options] Configuration options for the widget.
     * @param {Clock} [options.clock=new Clock()] The clock to use to control current time.
     * @param {ImageryProvider} [options.imageryProvider=new BingMapsImageryProvider()] The imagery provider to serve as the base layer. If set to false, no imagery provider will be added.
     * @param {TerrainProvider} [options.terrainProvider=new EllipsoidTerrainProvider] The terrain provider.
     * @param {SceneMode} [options.sceneMode=SceneMode.SCENE3D] The initial scene mode.
     * @param {Object} [options.useDefaultRenderLoop=true] True if this widget should control the render loop, false otherwise.
     * @param {Object} [options.contextOptions=undefined] Properties corresponding to <a href='http://www.khronos.org/registry/webgl/specs/latest/#5.2'>WebGLContextAttributes</a> used to create the WebGL context.  This object will be passed to the {@link Scene} constructor.
     *
     * @exception {DeveloperError} container is required.
     * @exception {DeveloperError} Element with id "container" does not exist in the document.
     *
     * @example
     * // For each example, include a link to CesiumWidget.css stylesheet in HTML head,
     * // and in the body, include: &lt;div id="cesiumContainer"&gt;&lt;/div&gt;
     *
     * //Widget with no terrain and default Bing Maps imagery provider.
     * var widget = new Cesium.CesiumWidget('cesiumContainer');
     *
     * //Widget with OpenStreetMaps imagery provider and Cesium terrain provider hosted by AGI.
     * var widget = new Cesium.CesiumWidget('cesiumContainer', {
     *     imageryProvider : new Cesium.OpenStreetMapImageryProvider(),
     *     terrainProvider : new Cesium.CesiumTerrainProvider({
     *         url : 'http://cesium.agi.com/smallterrain',
     *         credit : 'Terrain data courtesy Analytical Graphics, Inc.'
     *     })
     * });
     */
    var CesiumWidget = function(container, options) {
        if (typeof container === 'undefined') {
            throw new DeveloperError('container is required.');
        }

        container = getElement(container);

        options = defaultValue(options, {});

        //Configure the widget DOM elements
        var widgetNode = document.createElement('div');
        widgetNode.className = 'cesium-widget';
        container.appendChild(widgetNode);

        var canvas = document.createElement('canvas');
        canvas.oncontextmenu = function() {
            return false;
        };
        canvas.onselectstart = function() {
            return false;
        };
        widgetNode.appendChild(canvas);

        var creditContainer = document.createElement('div');
        creditContainer.className = 'cesium-widget-credits';
        widgetNode.appendChild(creditContainer);

        var scene = new Scene(canvas, options.contextOptions, creditContainer);
        scene.getCamera().controller.constrainedAxis = Cartesian3.UNIT_Z;

        var ellipsoid = Ellipsoid.WGS84;
        var creditDisplay = scene.getFrameState().creditDisplay;

        var cesiumCredit = new Credit('Cesium', cesiumLogoData, 'http://cesium.agi.com/');
        creditDisplay.addDefaultCredit(cesiumCredit);

        var centralBody = new CentralBody(ellipsoid);
        scene.getPrimitives().setCentralBody(centralBody);

        scene.skyBox = new SkyBox({
            positiveX : getDefaultSkyBoxUrl('px'),
            negativeX : getDefaultSkyBoxUrl('mx'),
            positiveY : getDefaultSkyBoxUrl('py'),
            negativeY : getDefaultSkyBoxUrl('my'),
            positiveZ : getDefaultSkyBoxUrl('pz'),
            negativeZ : getDefaultSkyBoxUrl('mz')
        });
        scene.skyAtmosphere = new SkyAtmosphere(ellipsoid);
        scene.sun = new Sun();

        //Set the base imagery layer
        var imageryProvider = options.imageryProvider;
        if (typeof imageryProvider === 'undefined') {
            imageryProvider = new BingMapsImageryProvider({
                url : 'http://dev.virtualearth.net',
                // Some versions of Safari support WebGL, but don't correctly implement
                // cross-origin image loading, so we need to load Bing imagery using a proxy.
                proxy : FeatureDetection.supportsCrossOriginImagery() ? undefined : new DefaultProxy('http://cesium.agi.com/proxy/')
            });
        }

        if (imageryProvider !== false) {
            centralBody.getImageryLayers().addImageryProvider(imageryProvider);
        }

        //Set the terrain provider if one is provided.
        if (typeof options.terrainProvider !== 'undefined') {
            centralBody.terrainProvider = options.terrainProvider;
        }

        this._element = widgetNode;
        this._container = container;
        this._canvas = canvas;
        this._canvasWidth = canvas.width;
        this._canvasHeight = canvas.height;
        this._scene = scene;
        this._centralBody = centralBody;
        this._clock = defaultValue(options.clock, new Clock());
        this._transitioner = new SceneTransitioner(scene, ellipsoid);
        this._screenSpaceEventHandler = new ScreenSpaceEventHandler(canvas);
        this._useDefaultRenderLoop = undefined;
        this._renderLoopRunning = false;
        this._creditContainer = creditContainer;
        this._canRender = false;
        if (options.sceneMode) {
            if (options.sceneMode === SceneMode.SCENE2D) {
                this._transitioner.to2D();
            }
            if (options.sceneMode === SceneMode.COLUMBUS_VIEW) {
                this._transitioner.toColumbusView();
            }
        }

        this.useDefaultRenderLoop = defaultValue(options.useDefaultRenderLoop, true);
    };

    defineProperties(CesiumWidget.prototype, {
        /**
         * Gets the parent container.
         * @memberof CesiumWidget.prototype
         *
         * @type {Element}
         */
        container : {
            get : function() {
                return this._container;
            }
        },

        /**
         * Gets the scene transitioner.
         * @memberof CesiumWidget.prototype
         *
         * @type {SceneTransitioner}
         */
        sceneTransitioner : {
            get : function() {
                return this._transitioner;
            }
        },

        /**
         * Gets the canvas.
         * @memberof CesiumWidget.prototype
         *
         * @type {Canvas}
         */
        canvas : {
            get : function() {
                return this._canvas;
            }
        },

        /**
         * Gets the credit container.
         * @memberof CesiumWidget.prototype
         *
         * @type {Element}
         */
        creditContainer: {
            get : function() {
                return this._creditContainer;
            }
        },

        /**
         * Gets the scene.
         * @memberof CesiumWidget.prototype
         *
         * @type {Scene}
         */
        scene : {
            get : function() {
                return this._scene;
            }
        },

        /**
         * Gets the primary central body.
         * @memberof CesiumWidget.prototype
         *
         * @type {CentralBody}
         */
        centralBody : {
            get : function() {
                return this._centralBody;
            }
        },

        /**
         * Gets the clock.
         * @memberof CesiumWidget.prototype
         *
         * @type {Clock}
         */
        clock : {
            get : function() {
                return this._clock;
            }
        },

        /**
         * Gets the screen space event handler.
         * @memberof CesiumWidget.prototype
         *
         * @type {ScreenSpaceEventHandler}
         */
        screenSpaceEventHandler : {
            get : function() {
                return this._screenSpaceEventHandler;
            }
        },

        /**
         * Gets the event that will be raised when an error is encountered during the default render loop.
         * The widget instance and the generated exception are the only two parameters passed to the event handler.
         * <code>useDefaultRenderLoop</code> will be set to false whenever an exception is generated and must
         * be set back to true to continue rendering after an exception.
         * @memberof Viewer.prototype
         * @type {Event}
         */
        onRenderLoopError : {
            get : function() {
                return this._onRenderLoopError;
            }
        },

        /**
         * Gets or sets whether or not this widget should control the render loop.
         * If set to true the widget will use {@link requestAnimationFrame} to
         * perform rendering and resizing of the widget, as well as drive the
         * simulation clock. If set to false, you must manually call the
         * <code>resize</code>, <code>render</code> methods as part of a custom
         * render loop.
         * @memberof CesiumWidget.prototype
         *
         * @type {Boolean}
         */
        useDefaultRenderLoop : {
            get : function() {
                return this._useDefaultRenderLoop;
            },
            set : function(value) {
                if (this._useDefaultRenderLoop !== value) {
                    this._useDefaultRenderLoop = value;
                    if (value && !this._renderLoopRunning) {
                        startRenderLoop(this);
                    }
                }
            }
        }
    });

    /**
     * @memberof CesiumWidget
     * @returns {Boolean} true if the object has been destroyed, false otherwise.
     */
    CesiumWidget.prototype.isDestroyed = function() {
        return false;
    };

    /**
     * Destroys the widget.  Should be called if permanently
     * removing the widget from layout.
     * @memberof CesiumWidget
     */
    CesiumWidget.prototype.destroy = function() {
        this._container.removeChild(this._element);
        destroyObject(this);
    };

    /**
     * Updates the canvas size, camera aspect ratio, and viewport size.
     * This function is called automatically as needed unless
     * <code>useDefaultRenderLoop</code> is set to false.
     * @memberof CesiumWidget
     */
    CesiumWidget.prototype.resize = function() {
        var canvas = this._canvas;
        var width = canvas.clientWidth;
        var height = canvas.clientHeight;
        if (this._canvasWidth === width && this._canvasHeight === height) {
            return;
        }

        canvas.width = this._canvasWidth = width;
        canvas.height = this._canvasHeight = height;

        var canRender = width !== 0 && height !== 0;
        this._canRender = canRender;

        if (canRender) {
            var frustum = this._scene.getCamera().frustum;
            if (typeof frustum.aspectRatio !== 'undefined') {
                frustum.aspectRatio = width / height;
            } else {
                frustum.top = frustum.right * (height / width);
                frustum.bottom = -frustum.top;
            }
        }
    };

    /**
     * Renders the scene.  This function is called automatically
     * unless <code>useDefaultRenderLoop</code> is set to false;
     * @memberof CesiumWidget
     */
    CesiumWidget.prototype.render = function() {
        this._scene.initializeFrame();
        var currentTime = this._clock.tick();
        if (this._canRender) {
            this._scene.render(currentTime);
        }
    };

    return CesiumWidget;
});