feat(hp callback): Add viewport ready callback (#3772)

Co-authored-by: Ouwen Huang <ouwen.huang@duke.edu>

extensions/cornerstone/src/commandsModule.ts

@@ -580,6 +580,23 @@ function commandsModule({
     storePresentation: ({ viewportId }) => {
       cornerstoneViewportService.storePresentation({ viewportId });
     },
+
+    attachProtocolViewportDataListener: ({ protocol, stageIndex }) => {
+      const EVENT = cornerstoneViewportService.EVENTS.VIEWPORT_DATA_CHANGED;
+      const command = protocol.callbacks.onViewportDataInitialized;
+      const numPanes = protocol.stages?.[stageIndex]?.viewports.length ?? 1;
+      let numPanesWithData = 0;
+      const { unsubscribe } = cornerstoneViewportService.subscribe(EVENT, evt => {
+        numPanesWithData++;
+
+        if (numPanesWithData === numPanes) {
+          commandsManager.run(...command);
+
+          // Unsubscribe from the event
+          unsubscribe(EVENT);
+        }
+      });
+    },
   };
 
   const definitions = {
@@ -606,7 +623,6 @@ function commandsModule({
       storeContexts: [],
       options: {},
     },
-
     deleteMeasurement: {
       commandFn: actions.deleteMeasurement,
     },
@@ -714,6 +730,9 @@ function commandsModule({
     cleanUpCrosshairs: {
       commandFn: actions.cleanUpCrosshairs,
     },
+    attachProtocolViewportDataListener: {
+      commandFn: actions.attachProtocolViewportDataListener,
+    },
   };
 
   return {