cesiumDemo/Source/Scene/NeverTileDiscardPolicy.js

    /**
     * A {@link TileDiscardPolicy} specifying that tile images should never be discard.
     *
     * @alias NeverTileDiscardPolicy
     * @constructor
     *
     * @see DiscardMissingTileImagePolicy
     */
    function NeverTileDiscardPolicy(options) {
    }

    /**
     * Determines if the discard policy is ready to process images.
     * @returns {Boolean} True if the discard policy is ready to process images; otherwise, false.
     */
    NeverTileDiscardPolicy.prototype.isReady = function() {
        return true;
    };

    /**
     * Given a tile image, decide whether to discard that image.
     *
     * @param {Image} image An image to test.
     * @returns {Boolean} True if the image should be discarded; otherwise, false.
     */
    NeverTileDiscardPolicy.prototype.shouldDiscardImage = function(image) {
        return false;
    };
export default NeverTileDiscardPolicy;