Add existing to tracked

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

@@ -0,0 +1,37 @@
+// @ts-check
+
+/**
+ * The alpha rendering mode of the material.
+ *
+ * @enum {string}
+ * @private
+ */
+const AlphaMode = {
+  /**
+   * The alpha value is ignored and the rendered output is fully opaque.
+   *
+   * @type {string}
+   * @constant
+   */
+  OPAQUE: "OPAQUE",
+
+  /**
+   * The rendered output is either fully opaque or fully transparent depending on the alpha value and the specified alpha cutoff value.
+   *
+   * @type {string}
+   * @constant
+   */
+  MASK: "MASK",
+
+  /**
+   * The rendered output is composited onto the destination with alpha blending.
+   *
+   * @type {string}
+   * @constant
+   */
+  BLEND: "BLEND",
+};
+
+Object.freeze(AlphaMode);
+
+export default AlphaMode;