Revert "Reduces redundant clamping on labels"

This reverts commit 83eb415e2a.

CHANGES.md

@@ -12,6 +12,7 @@
 - Improved performance and reduced memory usage of `Event` class. [#12896](https://github.com/CesiumGS/cesium/pull/12896)
 - Fixes vertical misalignment of glyphs in labels with small fonts [#8474](https://github.com/CesiumGS/cesium/issues/8474)
 - Prevent runtime errors for certain forms of invalid PNTS files [#12872](https://github.com/CesiumGS/cesium/issues/12872)
+- Improved performance of clamped labels [#12905](https://github.com/CesiumGS/cesium/pull/12905)
 
 #### Additions :tada:
 

packages/engine/Source/Scene/LabelCollection.js

@@ -11,7 +11,7 @@ import bitmapSDF from "bitmap-sdf";
 import BillboardCollection from "./BillboardCollection.js";
 import BillboardTexture from "./BillboardTexture.js";
 import BlendOption from "./BlendOption.js";
-import HeightReference, { isHeightReferenceClamp } from "./HeightReference.js";
+import { isHeightReferenceClamp } from "./HeightReference.js";
 import HorizontalOrigin from "./HorizontalOrigin.js";
 import Label from "./Label.js";
 import LabelStyle from "./LabelStyle.js";
@@ -307,8 +307,7 @@ function rebindAllGlyphs(labelCollection, label) {
     billboard.pixelOffset = label._pixelOffset;
     billboard.horizontalOrigin = HorizontalOrigin.LEFT;
     billboard.verticalOrigin = label._verticalOrigin;
-    // To avoid excessive height update listeners, glyphs are not clamped. Their height values are updated manually by the owning label.
-    billboard.heightReference = HeightReference.NONE;
+    billboard.heightReference = label._heightReference;
     billboard.scale = label.totalScale;
     billboard.pickPrimitive = label;
     billboard.id = label._id;

packages/engine/Specs/Scene/LabelCollectionSpec.js

@@ -2446,8 +2446,6 @@ describe("Scene/LabelCollection", function () {
           });
 
           expect(l._clampedPosition).toBeDefined();
-          // Glyphs are not truly clamped (to avoid excessive listeners and globe picks). They simply copy their owning label's clamped position.
-          expect(l._glyphs[0].billboard._clampedPosition).toBeUndefined();
 
           l.heightReference = HeightReference.NONE;
           expect(l._clampedPosition).toBeUndefined();
@@ -2459,8 +2457,8 @@ describe("Scene/LabelCollection", function () {
             heightReference: HeightReference.CLAMP_TO_GROUND,
             text: "t",
             position: Cartesian3.fromDegrees(-72.0, 40.0),
+            showBackground: true,
           });
-          l.showBackground = true;
 
           await pollToPromise(() => {
             scene.renderForSpecs();