Merge pull request #12905 from CesiumGS/label-clamping-performance

Reduces redundant clamping on labels

Author: ggetz

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)
 - Fixes issue where multiple instances of a Gaussian splat tileset would transform tile positions incorrectly and render out of position. [#12795](https://github.com/CesiumGS/cesium/issues/12795)
 
 #### Additions :tada:

packages/engine/Source/Scene/Billboard.js

@@ -227,6 +227,9 @@ function Billboard(options, billboardCollection) {
   this._updateClamping();
 
   this._splitDirection = options.splitDirection ?? SplitDirection.NONE;
+  // Primarily used by labels to indicate that the position is derived from the parent.
+  // and expensive operations like clamping can be skipped.
+  this._positionFromParent = false;
 }
 
 const SHOW_INDEX = (Billboard.SHOW_INDEX = 0);
@@ -1147,6 +1150,7 @@ Billboard._updateClamping = function (collection, owner) {
 
   if (
     owner._heightReference === HeightReference.NONE ||
+    owner._positionFromParent ||
     !defined(owner._position)
   ) {
     return;

packages/engine/Source/Scene/LabelCollection.js

@@ -294,6 +294,7 @@ function rebindAllGlyphs(labelCollection, label) {
         });
         billboard._labelDimensions = new Cartesian2();
         billboard._labelTranslate = new Cartesian2();
+        billboard._positionFromParent = true;
       }
       glyph.billboard = billboard;
     }

packages/engine/Specs/Scene/LabelCollectionSpec.js

@@ -2446,7 +2446,6 @@ describe("Scene/LabelCollection", function () {
           });
 
           expect(l._clampedPosition).toBeDefined();
-          expect(l._glyphs[0].billboard._clampedPosition).toBeDefined();
 
           l.heightReference = HeightReference.NONE;
           expect(l._clampedPosition).toBeUndefined();
@@ -2458,14 +2457,15 @@ describe("Scene/LabelCollection", function () {
             heightReference: HeightReference.CLAMP_TO_GROUND,
             text: "t",
             position: Cartesian3.fromDegrees(-72.0, 40.0),
+            showBackground: true,
           });
 
           await pollToPromise(() => {
             scene.renderForSpecs();
             return labelsWithHeight.ready;
           });
 
-          const billboard = l._glyphs[0].billboard;
+          const billboard = l._backgroundBillboard;
           expect(billboard._removeCallbackFunc).toBeDefined();
           const spy = spyOn(billboard, "_removeCallbackFunc");
           labelsWithHeight.remove(l);