action on ViewportPanes for setting the active viewport

platform/viewer/src/App.jsx

@@ -54,8 +54,8 @@ function App({ config, defaultExtensions }) {
     console.log(state, action);
 
     switch (action.type) {
-      case 'DO_TODO':
-        return state;
+      case 'SET_ACTIVE_VIEWPORT_INDEX':
+        return { ...state, ...{ activeViewportIndex: action.payload } };
       default:
         return action.payload;
     }

platform/viewer/src/components/ViewportGrid.jsx

@@ -12,6 +12,9 @@ function ViewerViewportGrid(props) {
     { numCols, numRows, activeViewportIndex, viewports },
     dispatch,
   ] = useViewportGrid();
+  const setActiveViewportIndex = index => {
+    dispatch({ type: 'SET_ACTIVE_VIEWPORT_INDEX', payload: index });
+  }
 
   // TODO -> Need some way of selecting which displaySets hit the viewports.
   const { DisplaySetService } = servicesManager.services;
@@ -97,6 +100,9 @@ function ViewerViewportGrid(props) {
             className="m-1"
             acceptDropsFor="displayset"
             onDrop={onDropHandler}
+            onScroll={() => { setActiveViewportIndex(viewportIndex); }}
+            onClick={() => { setActiveViewportIndex(viewportIndex); }}
+            onWheel={() => { setActiveViewportIndex(viewportIndex); }}
             isActive={activeViewportIndex === viewportIndex}
           >
             <EmptyViewport />