Made follow mode more robust.

src/index.ts

@@ -46,6 +46,14 @@ try {
     allowEIO3: true,
   });
 
+  // we want to keep track of the last position of the followed user's scene
+  // bounds so that we can send it to the new follower without having to
+  // make an interaction on the scene
+  const withLatestSceneBounds = new Map<
+    string,
+    { data: ArrayBuffer; iv: Uint8Array }
+  >();
+
   io.on("connection", (socket) => {
     ioDebug("connection established!");
     io.to(`${socket.id}`).emit("init-room");
@@ -77,6 +85,9 @@ try {
     socket.on(
       "server-volatile-broadcast",
       (roomID: string, encryptedData: ArrayBuffer, iv: Uint8Array) => {
+        if (roomID.startsWith("follow_")) {
+          withLatestSceneBounds.set(roomID, { data: encryptedData, iv });
+        }
         socketDebug(`${socket.id} sends volatile update to ${roomID}`);
         socket.volatile.broadcast
           .to(roomID)
@@ -89,19 +100,43 @@ try {
       switch (payload.action) {
         case "follow":
           await socket.join(roomID);
-          const sockets = await io.in(roomID).fetchSockets();
 
-          if (sockets.length === 1) {
-            io.to(payload.userToFollow.clientId).emit("broadcast-follow");
+          // Immediately send the latest scene bounds to the new follower
+          // without having to wait for a scene interaction
+          const latestSceneBounds = withLatestSceneBounds.get(roomID);
+          if (latestSceneBounds) {
+            io.to(socket.id).emit(
+              "client-broadcast",
+              latestSceneBounds.data,
+              latestSceneBounds.iv,
+            );
           }
 
+          const sockets = await io.in(roomID).fetchSockets();
+          const followedBy = sockets.map((socket) => socket.id);
+
+          // Notify the user to follow that someone has followed them
+          // More precisely, send the list of users that are following them
+          // so that they can make decisions based on that
+          io.to(payload.userToFollow.clientId).emit(
+            "follow-room-user-change",
+            followedBy,
+          );
+
           break;
         case "unfollow":
           await socket.leave(roomID);
           const _sockets = await io.in(roomID).fetchSockets();
+          const _followedBy = _sockets.map((socket) => socket.id);
+
+          io.to(payload.userToFollow.clientId).emit(
+            "follow-room-user-change",
+            _followedBy,
+          );
 
+          // cleanup
           if (_sockets.length === 0) {
-            io.to(payload.userToFollow.clientId).emit("broadcast-unfollow");
+            withLatestSceneBounds.delete(roomID);
           }
 
           break;