Redesign time sync to track frame advantage per peer

HeatXD · HeatXD · commit 2ab0065ca36a · 2026-02-24T17:16:37.000+01:00
diff --git a/GekkoLib/include/backend.h b/GekkoLib/include/backend.h
@@ -31,6 +31,30 @@ namespace Gekko {
 		bool IsValid(Frame current_ack, Frame current_last_input) const;
 	};
 
+	struct AdvantageHistory {
+	public:
+		void Init();
+
+		void Update(Frame frame);
+
+		f32 GetAverageAdvantage();
+
+		void SetLocalAdvantage(i8 adv);
+
+		void SetRemoteAdvantage(i8 adv);
+
+	private:
+		static const i32 HISTORY_SIZE = 26;
+
+        i8 _local_frame_adv;
+
+        i8 _remote_frame_adv;
+
+		i8 _local[HISTORY_SIZE];
+
+		i8 _remote[HISTORY_SIZE];
+	};
+
 	class Player
 	{
 	public:
@@ -61,38 +85,14 @@ namespace Gekko {
 
 		u64 last_input_send_time = 0;
 
+		AdvantageHistory adv_history;
+
 	private:
         GekkoPlayerType _type;
 
 		PlayerStatus _status;
 	};
 
-	struct AdvantageHistory {
-	public:
-		void Init();
-
-		void Update(Frame frame);
-
-		f32 GetAverageAdvantage();
-
-		i8 GetLocalAdvantage();
-
-		void SetLocalAdvantage(i8 adv);
-
-		void SetRemoteAdvantage(i8 adv);
-
-	private:
-		static const i32 HISTORY_SIZE = 32;
-
-        i8 _local_frame_adv;
-
-        i8 _remote_frame_adv;
-
-		i8 _local[HISTORY_SIZE];
-
-		i8 _remote[HISTORY_SIZE];
-	};
-
 	class MessageSystem {
 	public:
 		MessageSystem();
@@ -107,7 +107,7 @@ namespace Gekko {
 
 		void HandleData(GekkoNetAdapter* host, GekkoNetResult** data, u32 length);
 
-		void SendInputAck(Handle player, Frame frame);
+		void SendInputAck(Handle player, Frame frame, i8 local_advantage);
 
 		Frame GetLastAddedInput(bool spectator = false);
 
@@ -128,9 +128,7 @@ namespace Gekko {
 
 		std::vector<std::unique_ptr<Player>> spectators;
 
-		AdvantageHistory history;
-
-        SessionEventSystem session_events;
+		SessionEventSystem session_events;
 
         std::map<Frame, u32> local_health;
 
diff --git a/GekkoLib/include/session.h b/GekkoLib/include/session.h
@@ -75,8 +75,6 @@ namespace Gekko {
 
 		void HandleSavingConfirmedFrame();
 
-		void UpdateLocalFrameAdvantage();
-
         void SendSessionHealthCheck();
 
         void SendNetworkHealthCheck();
diff --git a/GekkoLib/src/backend.cpp b/GekkoLib/src/backend.cpp
@@ -25,7 +25,6 @@ Gekko::MessageSystem::MessageSystem()
 	std::srand((unsigned int)std::time(nullptr));
 	_session_magic = std::rand();
 
-	history = AdvantageHistory();
     session_events = SessionEventSystem();
 }
 
@@ -36,7 +35,6 @@ void Gekko::MessageSystem::Init(u8 num_players, u32 input_size)
 
     _net_player_queue.resize(num_players);
 
-	history.Init();
 }
 
 
@@ -198,7 +196,7 @@ void Gekko::MessageSystem::SendSyncResponse(NetAddress* addr, u16 magic)
     message->pkt.body = std::move(body);
 }
 
-void Gekko::MessageSystem::SendInputAck(Handle player, Frame frame)
+void Gekko::MessageSystem::SendInputAck(Handle player, Frame frame, i8 local_advantage)
 {
 	auto plyr = GetPlayerByHandle(player);
 
@@ -215,7 +213,7 @@ void Gekko::MessageSystem::SendInputAck(Handle player, Frame frame)
 
     auto body = std::make_unique<InputAckMsg>();
 	body->ack_frame = frame;
-	body->frame_advantage = history.GetLocalAdvantage();
+	body->frame_advantage = local_advantage;
 
     message->pkt.body = std::move(body);
 }
@@ -619,7 +617,6 @@ void Gekko::MessageSystem::OnInputs(NetAddress& addr, NetPacket& pkt)
 
     const Frame start_frame = body->start_frame;
     const u32 input_count = body->input_count;
-    const Frame end_frame = start_frame + input_count;
 
     const bool is_spectator = (pkt.header.type == SpectatorInputs);
 
@@ -657,29 +654,19 @@ void Gekko::MessageSystem::OnInputs(NetAddress& addr, NetPacket& pkt)
 void Gekko::MessageSystem::OnInputAck(NetAddress& addr, NetPacket& pkt)
 {
     auto body = (InputAckMsg*)pkt.body.get();
-    // we should just update the ack frame for all handles where the address matches
-	const Frame ack_frame = body->ack_frame;
-    const i32 remote_advantage = body->frame_advantage;
-    bool added_advantage = false;
+    const Frame ack_frame = body->ack_frame;
+    const i8 remote_advantage = (i8)body->frame_advantage;
 
-    std::vector<std::unique_ptr<Player>>* current = &remotes;
-    for (u32 i = 0; i < 2; i++)
-    {
-        if (i == 1) {
-            current = &spectators;
+    for (auto& player : remotes) {
+        if (player->address.Equals(addr) && player->stats.last_acked_frame < ack_frame) {
+            player->stats.last_acked_frame = ack_frame;
+            player->adv_history.SetRemoteAdvantage(remote_advantage);
         }
+    }
 
-        for (auto& player : *current) {
-            if (player->address.Equals(addr)) {
-                if (player->stats.last_acked_frame < ack_frame) {
-                    player->stats.last_acked_frame = ack_frame;
-                    // only add remote advantages once
-                    if (!added_advantage && i == 0) {
-                        history.SetRemoteAdvantage(remote_advantage);
-                        added_advantage = true;
-                    }
-                }
-            }
+    for (auto& player : spectators) {
+        if (player->address.Equals(addr) && player->stats.last_acked_frame < ack_frame) {
+            player->stats.last_acked_frame = ack_frame;
         }
     }
 }
@@ -923,6 +910,3 @@ void Gekko::AdvantageHistory::SetRemoteAdvantage(i8 adv) {
     _remote_frame_adv = adv;
 }
 
-i8 Gekko::AdvantageHistory::GetLocalAdvantage() {
-	return _local_frame_adv;
-}
diff --git a/GekkoLib/src/game_session.cpp b/GekkoLib/src/game_session.cpp
@@ -168,7 +168,15 @@ f32 Gekko::GameSession::FramesAhead()
         return 0.f;
     }
 
-	return _msg.history.GetAverageAdvantage();
+    f32 sum = 0.f;
+    i32 count = 0;
+    for (auto& remote : _msg.remotes) {
+        if (remote->GetStatus() == Connected) {
+            sum += remote->adv_history.GetAverageAdvantage();
+            count++;
+        }
+    }
+    return count > 0 ? sum / (f32)count : 0.f;
 }
 
 void Gekko::GameSession::NetworkStats(i32 player, GekkoNetworkStats* stats)
@@ -236,19 +244,6 @@ void Gekko::GameSession::HandleSavingConfirmedFrame()
 	assert(_sync.GetCurrentFrame() == current);
 }
 
-void Gekko::GameSession::UpdateLocalFrameAdvantage()
-{
-    if (!_started) {
-        return;
-    }
-
-	const Frame min = _sync.GetMinReceivedFrame();
-	const Frame current = _sync.GetCurrentFrame();
-    const i32 local_advantage = current - min;
-
-	_msg.history.SetLocalAdvantage(local_advantage);
-}
-
 void Gekko::GameSession::SendSessionHealthCheck()
 {
     if (!_config.desync_detection) {
@@ -406,9 +401,6 @@ void Gekko::GameSession::Poll()
 	// handle received inputs
 	HandleReceivedInputs();
 
-	// update local frame advantage
-	UpdateLocalFrameAdvantage();
-
 	// add local input for the network
 	SendLocalInputs();
 
@@ -454,12 +446,15 @@ void Gekko::GameSession::HandleReceivedInputs()
 
             auto& input_q = _msg.GetNetPlayerQueue(handle);
             const Frame min_frame = last_added - (i32)input_q.size() + 1;
+            const Frame current_frame = _sync.GetCurrentFrame();
+            const Frame local_delay = (Frame)GetMinLocalDelay();
             for (int i = last_recv; i <= last_added; i++) {
                 if (i >= min_frame) {
                     int current_idx = i - min_frame;
                     u8* input = input_q[current_idx].get();
                     _sync.AddRemoteInput(handle, input, i);
-                    _msg.SendInputAck(handle, i);
+                    const i8 local_adv = (i8)(current_frame - i - local_delay);
+                    _msg.SendInputAck(handle, i, local_adv);
                 }
             }
         }
@@ -480,9 +475,16 @@ void Gekko::GameSession::SendLocalInputs()
                 }
                 _msg.AddInput(frame, player->handle, input.get());
             }
-            // Record advantage snapshot once per actual game frame
+            // Record per-peer advantage snapshot once per actual game frame
             if (frame == current) {
-                _msg.history.Update(frame);
+                const Frame current_frame = _sync.GetCurrentFrame();
+                for (auto& remote : _msg.remotes) {
+                    if (remote->GetStatus() == Connected) {
+                        const i8 local_adv = (i8)(current_frame - _sync.GetLastReceivedFrom(remote->handle) - (Frame)delay);
+                        remote->adv_history.SetLocalAdvantage(local_adv);
+                        remote->adv_history.Update(frame);
+                    }
+                }
             }
 		}
 	}
diff --git a/GekkoLib/src/player.cpp b/GekkoLib/src/player.cpp
@@ -14,6 +14,7 @@ Gekko::Player::Player(Handle phandle, GekkoPlayerType type, NetAddress* addr, u3
 
 	_type = type;
 	_status = _type == GekkoLocalPlayer ? Connected : Initiating;
+	adv_history.Init();
 }
 
 GekkoPlayerType Gekko::Player::GetType()
diff --git a/GekkoLib/src/spectator_session.cpp b/GekkoLib/src/spectator_session.cpp
@@ -204,7 +204,7 @@ void Gekko::SpectatorSession::HandleReceivedInputs()
                     int current_idx = i - min_frame;
                     u8* input = input_q[current_idx].get();
                     _sync.AddRemoteInput(handle, input, i);
-                    _msg.SendInputAck(handle, i);
+                    _msg.SendInputAck(handle, i, 0);
                 }
             }
         }

Original file line number	Diff line number	Diff line change
`@@ -14,6 +14,7 @@ Gekko::Player::Player(Handle phandle, GekkoPlayerType type, NetAddress* addr, u3`
`14`	`14`
`15`	`15`	`_type = type;`
`16`	`16`	`_status = _type == GekkoLocalPlayer ? Connected : Initiating;`
	`17`	`+ adv_history.Init();`
`17`	`18`	`}`
`18`	`19`
`19`	`20`	`GekkoPlayerType Gekko::Player::GetType()`
Original file line number	Diff line number	Diff line change
`@@ -204,7 +204,7 @@ void Gekko::SpectatorSession::HandleReceivedInputs()`
`204`	`204`	`int current_idx = i - min_frame;`
`205`	`205`	`u8* input = input_q[current_idx].get();`
`206`	`206`	`_sync.AddRemoteInput(handle, input, i);`
`207`		`- _msg.SendInputAck(handle, i);`
	`207`	`+ _msg.SendInputAck(handle, i, 0);`
`208`	`208`	`}`
`209`	`209`	`}`
`210`	`210`	`}`