fix(hydration): Maintain the same slice that the user was on pre hydration in post hydration for SR and SEG. (#4200)

extensions/cornerstone-dicom-seg/src/utils/hydrationUtils.ts

@@ -11,6 +11,7 @@ import { Enums, cache } from '@cornerstonejs/core';
  * @param params.loadFn - Function to load the segmentation data.
  * @param params.servicesManager - The services manager.
  * @param params.displaySet -  the display set.
+ * @param params.initialSliceIndex - The initial slice index.
  *
  * @returns Returns true upon successful update of viewports for segmentation rendering.
  */
@@ -19,11 +20,13 @@ async function updateViewportsForSegmentationRendering({
   loadFn,
   servicesManager,
   displaySet,
+  initialSliceIndex = null,
 }: {
   viewportId: string;
   loadFn: () => Promise<string>;
   servicesManager: AppTypes.ServicesManager;
   displaySet?: any;
+  initialSliceIndex?: number;
 }) {
   const { cornerstoneViewportService, segmentationService, viewportGridService } =
     servicesManager.services;
@@ -61,6 +64,14 @@ async function updateViewportsForSegmentationRendering({
     };
     const viewportId = viewport.viewportId;
 
+    // maintain the prehydration slice on the target viewport only
+    if (viewportId === targetViewportId) {
+      viewport.viewportOptions.initialImageOptions = {
+        index: initialSliceIndex,
+        useOnce: true,
+      };
+    }
+
     const csViewport = cornerstoneViewportService.getCornerstoneViewport(viewportId);
     const prevCamera = csViewport.getCamera();