GroundPrimitive changes color is invalid

111 · September 20, 2018, 7:08am

var handler = new Cesium.ScreenSpaceEventHandler(viewer.canvas);
handler.setInputAction(function (movement) {

    var pickedObject = viewer.scene.pick(movement.position);
    var attributes = groundPrimitive.getGeometryInstanceAttributes('123');

attributes.color = Cesium.ColorGeometryInstanceAttribute.toValue(Cesium.Color.YELLOW);
console.log(attributes)
}, Cesium.ScreenSpaceEventType.LEFT_CLICK);

111 · September 20, 2018, 7:09am

I tried again and found that when the length of the geometryInstances array is 1, changing the color can take effect. When the length of the geometryInstances array is greater than 2, changing the color will be invalid.

omar · September 20, 2018, 6:18pm

It looks like this is because GroundPrimitive uses ClassificationPrimitive, which only supports the same color across all instances:

https://cesiumjs.org/Cesium/Build/Documentation/ClassificationPrimitive.html

The ‘color’ in this array is what prevents it from allowing you to do this:

github.com

CesiumGS/cesium/blob/master/Source/Scene/ClassificationPrimitive.js#L57


* are also valid if they are extruded volumes; otherwise, they will not be rendered.
* </p>
*
* @alias ClassificationPrimitive
* @constructor
*
* @param {Object} [options] Object with the following properties:
* @param {Array|GeometryInstance} [options.geometryInstances] The geometry instances to render. This can either be a single instance or an array of length one.
* @param {Appearance} [options.appearance] The appearance used to render the primitive. Defaults to PerInstanceColorAppearance when GeometryInstances have a color attribute.
* @param {Boolean} [options.show=true] Determines if this primitive will be shown.
* @param {Boolean} [options.vertexCacheOptimize=false] When <code>true</code>, geometry vertices are optimized for the pre and post-vertex-shader caches.
* @param {Boolean} [options.interleave=false] When <code>true</code>, geometry vertex attributes are interleaved, which can slightly improve rendering performance but increases load time.
* @param {Boolean} [options.compressVertices=true] When <code>true</code>, the geometry vertices are compressed, which will save memory.
* @param {Boolean} [options.releaseGeometryInstances=true] When <code>true</code>, the primitive does not keep a reference to the input <code>geometryInstances</code> to save memory.
* @param {Boolean} [options.allowPicking=true] When <code>true</code>, each geometry instance will only be pickable with {@link Scene#pick}.  When <code>false</code>, GPU memory is saved.
* @param {Boolean} [options.asynchronous=true] Determines if the primitive will be created asynchronously or block until ready. If false initializeTerrainHeights() must be called first.
* @param {ClassificationType} [options.classificationType=ClassificationType.BOTH] Determines whether terrain, 3D Tiles or both will be classified.
* @param {Boolean} [options.debugShowBoundingVolume=false] For debugging only. Determines if this primitive's commands' bounding spheres are shown.
* @param {Boolean} [options.debugShowShadowVolume=false] For debugging only. Determines if the shadow volume for each geometry in the primitive is drawn. Must be <code>true</code> on
*                  creation for the volumes to be created before the geometry is released or options.releaseGeometryInstance must be <code>false</code>.
*

You can see it gets set when there’s more than one instance:

github.com

CesiumGS/cesium/blob/master/Source/Scene/ClassificationPrimitive.js#L203




Object.defineProperties(ClassificationPrimitive.prototype, {
    /**
     * When <code>true</code>, geometry vertices are optimized for the pre and post-vertex-shader caches.
     *
     * @memberof ClassificationPrimitive.prototype
     *
     * @type {Boolean}
     * @readonly
     *
     * @default true
     */
    vertexCacheOptimize : {
        get : function() {
            return this._primitiveOptions.vertexCacheOptimize;
        }
    },


    /**
     * Determines if geometry vertex attributes are interleaved, which can slightly improve rendering performance.
     *