chore(Billboards): Add deprecation notice for legacy WebGL fallbacks

Author: donmccurdy

CHANGES.md

@@ -1,5 +1,13 @@
 # Change Log
 
+## 1.137
+
+### @cesium/engine
+
+#### Deprecated :hourglass_flowing_sand:
+
+- Beginning in CesiumJS 1.140, billboards and labels will require device support for WebGL 2, or WebGL 1 with ANGLE_instanced_arrays and MAX_VERTEX_TEXTURE_IMAGE_UNITS > 0. For more information or to share feedback, please see [#13053](https://github.com/CesiumGS/cesium/issues/13053). [#13067](https://github.com/CesiumGS/cesium/issues/13067)
+
 ## 1.136 - 2025-12-01
 
 ### @cesium/engine

packages/engine/Source/Scene/BillboardCollection.js

@@ -35,6 +35,7 @@ import TextureAtlas from "../Renderer/TextureAtlas.js";
 import VerticalOrigin from "./VerticalOrigin.js";
 import Ellipsoid from "../Core/Ellipsoid.js";
 import WebGLConstants from "../Core/WebGLConstants.js";
+import deprecationWarning from "../Core/deprecationWarning.js";
 
 const SHOW_INDEX = Billboard.SHOW_INDEX;
 const POSITION_INDEX = Billboard.POSITION_INDEX;
@@ -1784,6 +1785,19 @@ BillboardCollection.prototype.update = function (frameState) {
   }
 
   const context = frameState.context;
+
+  if (
+    !context.instancedArrays ||
+    !(ContextLimits.maximumVertexTextureImageUnits > 0)
+  ) {
+    deprecationWarning(
+      "Billboard-unsupported-ANGLE_instanced_arrays",
+      "Beginning in CesiumJS 1.140, billboards and labels will require device support for WebGL 2, " +
+        "or WebGL 1 with ANGLE_instanced_arrays and MAX_VERTEX_TEXTURE_IMAGE_UNITS > 0. For more " +
+        "information or to share feedback, see: https://github.com/CesiumGS/cesium/issues/13053",
+    );
+  }
+
   this._instanced = context.instancedArrays;
   attributeLocations = this._instanced
     ? attributeLocationsInstanced