Add existing to tracked

node_modules/@cesium/engine/Source/Scene/DiscardEmptyTileImagePolicy.js

@@ -0,0 +1,54 @@
+import defined from "../Core/defined.js";
+
+/**
+ * A policy for discarding tile images that contain no data (and so aren't actually images).
+ * This policy discards {@link DiscardEmptyTileImagePolicy.EMPTY_IMAGE}, which is
+ * expected to be used in place of any empty tile images by the image loading code.
+ *
+ * @alias DiscardEmptyTileImagePolicy
+ * @constructor
+ *
+ * @see DiscardMissingTileImagePolicy
+ */
+function DiscardEmptyTileImagePolicy(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.
+ */
+DiscardEmptyTileImagePolicy.prototype.isReady = function () {
+  return true;
+};
+
+/**
+ * Given a tile image, decide whether to discard that image.
+ *
+ * @param {HTMLImageElement} image An image to test.
+ * @returns {boolean} True if the image should be discarded; otherwise, false.
+ */
+DiscardEmptyTileImagePolicy.prototype.shouldDiscardImage = function (image) {
+  return DiscardEmptyTileImagePolicy.EMPTY_IMAGE === image;
+};
+
+let emptyImage;
+
+Object.defineProperties(DiscardEmptyTileImagePolicy, {
+  /**
+   * Default value for representing an empty image.
+   * @type {HTMLImageElement}
+   * @readonly
+   * @memberof DiscardEmptyTileImagePolicy
+   */
+  EMPTY_IMAGE: {
+    get: function () {
+      if (!defined(emptyImage)) {
+        emptyImage = new Image();
+        // load a blank data URI with a 1x1 transparent pixel.
+        emptyImage.src =
+          "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII=";
+      }
+      return emptyImage;
+    },
+  },
+});
+export default DiscardEmptyTileImagePolicy;