fix(cornerstone): share one color LUT across a segmentation's viewport representations

extensions/cornerstone/src/services/SegmentationService/SegmentationService.test.ts

@@ -1331,6 +1331,51 @@ describe('SegmentationService', () => {
 
       expect(retrievedSegmentationId).toEqual(segmentationId);
     });
+
+    it('should create a dedicated color LUT and remember its index so every viewport representation reuses it', async () => {
+      const displaySet = {
+        imageIds: ['imageId'],
+        isDynamicVolume: false,
+        SeriesNumber: 1,
+        SeriesDescription: 'Series Description',
+      } as unknown as AppTypes.DisplaySet;
+
+      jest
+        .spyOn(imageLoader, 'createAndCacheDerivedLabelmapImages')
+        .mockReturnValue([{ imageId: 'imageId' }] as csTypes.IImage[]);
+      jest.spyOn(cstSegmentation.state, 'getSegmentations').mockReturnValue([]);
+      jest.spyOn(service, 'addOrUpdateSegmentation').mockReturnValue(undefined);
+      jest.mocked(cstSegmentation.state.addColorLUT).mockReturnValue(7);
+
+      const segmentationId = await service.createLabelmapForDisplaySet(displaySet);
+
+      expect(cstSegmentation.state.addColorLUT).toHaveBeenCalledWith([[0, 0, 0, 0]]);
+      expect(service['_segmentationIdToColorLUTIndexMap'].get(segmentationId)).toBe(7);
+    });
+
+    it('should keep the existing color LUT when called again with the same segmentation id', async () => {
+      const displaySet = {
+        imageIds: ['imageId'],
+        isDynamicVolume: false,
+        SeriesNumber: 1,
+        SeriesDescription: 'Series Description',
+      } as unknown as AppTypes.DisplaySet;
+
+      jest
+        .spyOn(imageLoader, 'createAndCacheDerivedLabelmapImages')
+        .mockReturnValue([{ imageId: 'imageId' }] as csTypes.IImage[]);
+      jest.spyOn(cstSegmentation.state, 'getSegmentations').mockReturnValue([]);
+      jest.spyOn(service, 'addOrUpdateSegmentation').mockReturnValue(undefined);
+      jest.mocked(cstSegmentation.state.addColorLUT).mockReturnValueOnce(7).mockReturnValueOnce(8);
+
+      const segmentationId = await service.createLabelmapForDisplaySet(displaySet);
+      await service.createLabelmapForDisplaySet(displaySet, { segmentationId });
+
+      // Updating an existing segmentation must not strand the representations
+      // already rendering it on the previous LUT.
+      expect(cstSegmentation.state.addColorLUT).toHaveBeenCalledTimes(1);
+      expect(service['_segmentationIdToColorLUTIndexMap'].get(segmentationId)).toBe(7);
+    });
   });
 
   describe('createSegmentationForSEGDisplaySet', () => {

extensions/cornerstone/src/services/SegmentationService/SegmentationService.ts

@@ -512,6 +512,19 @@ class SegmentationService extends PubSubService implements ISegmentationServiceI
       },
     };
 
+    // Create a dedicated color LUT up front and remember its index so that every
+    // representation of this segmentation (one per viewport) reuses the same LUT.
+    // Otherwise each viewport would get its own default LUT copy and editing a
+    // segment color on one viewport would not be reflected on the others (the
+    // segment color appears to revert to the default when interacting elsewhere).
+    // The caller may pass the id of an existing segmentation, which this method
+    // updates rather than replaces; keep its LUT so representations already
+    // rendering it don't diverge from the ones created afterwards.
+    if (!this._segmentationIdToColorLUTIndexMap.has(segmentationId)) {
+      const colorLUTIndex = addColorLUT([[0, 0, 0, 0]] as csTypes.ColorLUT);
+      this._segmentationIdToColorLUTIndexMap.set(segmentationId, colorLUTIndex);
+    }
+
     this.addOrUpdateSegmentation(segmentationPublicInput);
     return segmentationId;
   }