Add support for SET_LAYOUT action on viewportGrid reducer

platform/viewer/src/App.jsx

@@ -64,13 +64,33 @@ function App({ config, defaultExtensions }) {
     switch (action.type) {
       case 'SET_ACTIVE_VIEWPORT_INDEX':
         return { ...state, ...{ activeViewportIndex: action.payload } };
-      case 'SET_DISPLAYSET_FOR_VIEWPORT':
+      case 'SET_DISPLAYSET_FOR_VIEWPORT': {
         const { viewportIndex, displaySetInstanceUID } = action.payload;
         const viewports = state.viewports.slice();
 
         viewports[viewportIndex] = { displaySetInstanceUID };
 
         return { ...state, ...{ viewports } };
+      }
+      case 'SET_LAYOUT': {
+        const { numCols, numRows } = action.payload;
+        const numPanes = numCols * numRows;
+        const viewports = state.viewports.slice();
+        const activeViewportIndex =
+          state.activeViewportIndex >= numPanes ? 0 : state.activeViewportIndex;
+
+        while (viewports.length < numPanes) {
+          viewports.push({});
+        }
+        while (viewports.length > numPanes) {
+          viewports.pop();
+        }
+
+        return {
+          ...state,
+          ...{ activeViewportIndex, numCols, numRows, viewports },
+        };
+      }
       default:
         return action.payload;
     }