#5 - fixed interpolation & rollback

README.md

@@ -27,8 +27,8 @@ $ conan install . --output-folder=build --build=missing -s build_type=Debug
 Configure and build using the generated preset:
 
 ```bash
-$ cmake --preset conan-debug
-$ cmake --build --preset conan-debug
+$ cmake -S . -B ./build -DCMAKE_TOOLCHAIN_FILE="build/conan_toolchain.cmake" -DCMAKE_BUILD_TYPE=Debug
+$ cmake --build ./build
 ```
 
 For a release build, repeat both steps with `-s build_type=Release` and the

compose.yaml

@@ -1,6 +1,6 @@
 services:
   timescaledb:
-    image: timescale/timescaledb:latest-pg16
+    image: timescale/timescaledb:latest-pg15
     restart: unless-stopped
     environment:
       POSTGRES_USER: mmo
@@ -9,7 +9,7 @@ services:
     ports:
       - "5432:5432"
     volumes:
-      - timescaledb_data:/var/lib/postgresql/data
+      - timescaledb_data:/var/lib/towards_db/data
 
   grafana:
     image: grafana/grafana:latest
@@ -24,15 +24,6 @@ services:
     depends_on:
       - timescaledb
 
-  # The zone server is not containerised yet: it needs libpqxx >= 7.7 for
-  # pqxx::params and jammy carries 6.4.
-
-  # ── e2e harness ────────────────────────────────────────────────────────────
-  # Opt in with `--profile e2e`, so a plain `docker compose up` still brings up
-  # the database and dashboards on their own.
-  #
-  #   docker compose --profile e2e up --build \
-  #       --abort-on-container-exit --exit-code-from chat-mock-client
   chat-server:
     profiles: [e2e]
     build:

modules/client/shaders/Opaque.frag

@@ -2,6 +2,9 @@
 
 layout(location = 0) out vec4 outColor;
 
+layout(location = 0) in vec3 inNormal;
+
 void main() {
+    float diffuse = max(0.1, dot(vec3(0.8, 1.5, -1.0), inNormal));
     outColor = vec4(1.0, 0.0, 0.0, 1.0);
 }

modules/client/shaders/Opaque.vert

@@ -2,6 +2,7 @@
 
 layout(location = 0) in vec3 pos;
 layout(location = 1) in vec3 norm;
+layout(location = 0) out vec3 outNormal;
 
 layout(set = 0, binding = 0) uniform Camera {
 	mat4 proj;
@@ -21,5 +22,6 @@ void main() {
 	// outPos = pos.xyz * 0.05;
 	// outNormal = norm.xyz;
 	// outUV = uv;
+    outNormal = norm;
     gl_Position = cam.proj * cam.view * PushConstants.transform *  vec4(pos, 1.0);
 }

modules/client/src/debug/EntityInterpolationDebug.hpp

@@ -101,10 +101,54 @@ class tw::dbg::ComponentGui<tw::net::EntityPositionInterpolation> {
 private:
     using Clock = std::chrono::high_resolution_clock;
 
+    /** How far back the plot reaches. */
+    static constexpr float WINDOW_IN_SECONDS = 10.0f;
+
+    /** Ten seconds of frames at sixty a second. */
+    static constexpr size_t CAPACITY = 600;
+
+    inline static const net::EntityPositionInterpolation* m_subject = nullptr;
+
+    inline static int    m_last_frame = -1;
+    inline static size_t m_head       = 0;
+    inline static size_t m_count      = 0;
+
+    inline static std::vector<Clock::time_point> m_read_times;
+    inline static std::vector<glm::vec3>         m_read_values;
+
     static int64_t millis_since(Clock::time_point point) {
         return std::chrono::duration_cast<std::chrono::milliseconds>(Clock::now() - point).count();
     }
 
+    void restart(const net::EntityPositionInterpolation* instance) {
+        m_subject    = instance;
+        m_last_frame = -1;
+        m_head       = 0;
+        m_count      = 0;
+
+        m_read_times.resize(CAPACITY);
+        m_read_values.resize(CAPACITY);
+    }
+
+    /**
+     * Keeps one reading per frame, so drawing twice does not double up. The
+     * whole value is kept rather than the axis on show, so switching axis
+     * still shows the trace that was already gathered.
+     */
+    void sample(Clock::time_point time, glm::vec3 value) {
+        const int frame = ImGui::GetFrameCount();
+        if(m_last_frame == frame) {
+            return;
+        }
+        m_last_frame = frame;
+
+        m_read_times[m_head]  = time;
+        m_read_values[m_head] = value;
+
+        m_head  = (m_head + 1) % CAPACITY;
+        m_count = std::min(m_count + 1, CAPACITY);
+    }
+
 public:
     void draw(net::EntityPositionInterpolation* instance) {
         ImGui::SeparatorText("Received Positions");
@@ -122,5 +166,73 @@ public:
             instance->values()[0].y,
             instance->values()[0].z,
             millis_since(instance->times()[0]));
+
+        static int axis = 0;
+        ImGui::Combo("Axis##received", &axis, "X\0Y\0Z\0");
+
+        /** How far behind the present the reader looks; matches the caller. */
+        static int delay_in_millis = 1000;
+        ImGui::SliderInt("Delay (ms)", &delay_in_millis, 0, 2000);
+
+        if(m_subject != instance) {
+            restart(instance);
+        }
+
+        // The buffer wraps, so the index says nothing about when a sample
+        // arrived. Placing each one at its own age puts it where it belongs
+        // without having to know where the ring currently starts. Slots
+        // nothing was pushed into are left out.
+        const auto   now   = Clock::now();
+        const size_t count = instance->size();
+
+        std::vector<float> ages(count);
+        std::vector<float> positions(count);
+
+        for(size_t i = 0; i < count; i++) {
+            ages[i]      = -std::chrono::duration<float>(now - instance->times()[i]).count();
+            positions[i] = instance->values()[i][axis];
+        }
+
+        if(ImPlot::BeginPlot("Buffer", ImVec2(-1.0f, 180.0f))) {
+            ImPlot::SetupAxes("seconds ago", "position", ImPlotAxisFlags_None, ImPlotAxisFlags_AutoFit);
+            ImPlot::SetupAxisLimits(ImAxis_X1,
+                -WINDOW_IN_SECONDS, 0.0f, ImGuiCond_Always);
+
+            ImPlot::PlotScatter("Received", ages.data(), positions.data(), (int)count);
+
+            // Reading the same way the position is read for drawing shows
+            // which two samples the delay lands between, and how far the
+            // result sits from either of them.
+            const auto point = now - std::chrono::milliseconds(delay_in_millis);
+            const auto [from, to, alpha] = instance->get_values_around(point);
+
+            const float read_at  = -std::chrono::duration<float>(now - point).count();
+            const float read_out = glm::mix(from, to, alpha)[axis];
+
+            ImPlot::SetNextMarkerStyle(ImPlotMarker_Circle, 5.0f);
+            ImPlot::PlotScatter("Interpolated", &read_at, &read_out, 1);
+
+            // Each reading is kept at the moment it was read for, so the trace
+            // ends on the marker above and runs back along the same timeline
+            // the received samples sit on.
+            sample(point, glm::mix(from, to, alpha));
+
+            std::vector<float> trace_ages(m_count);
+            std::vector<float> trace_positions(m_count);
+
+            const size_t oldest = m_count == CAPACITY ? m_head : 0;
+
+            for(size_t i = 0; i < m_count; i++) {
+                const size_t index = (oldest + i) % CAPACITY;
+
+                trace_ages[i]      = -std::chrono::duration<float>(now - m_read_times[index]).count();
+                trace_positions[i] = m_read_values[index][axis];
+            }
+
+            ImPlot::PlotLine("Interpolated Trace",
+                trace_ages.data(), trace_positions.data(), (int)m_count);
+
+            ImPlot::EndPlot();
+        }
     }
 };

modules/client/src/network/EntityPositionInterpolator.cpp

@@ -25,7 +25,7 @@ void EntityPositionInterpolator::set_position(Clock::time_point time_point, entt
         return;
     }
 
-    interpolation->push(Clock::now(), position);
+    interpolation->push(time_point, position);
 }
 
 glm::vec3 EntityPositionInterpolator::get_position(Clock::time_point time_point, entt::entity entity) {
@@ -35,9 +35,7 @@ glm::vec3 EntityPositionInterpolator::get_position(Clock::time_point time_point,
         return glm::vec3();
     }
 
-    auto now = Clock::now() - std::chrono::milliseconds(m_bufferingIntervalInMillis);
-
-    auto [from, to, value] = interpolation->get_values_around(now);
+    auto [from, to, value] = interpolation->get_values_around(time_point);
     return glm::mix(from, to, value);
 }
 
@@ -45,6 +43,10 @@ void EntityPositionInterpolator::interpolate_smoothed_entities(Clock::time_point
     m_registry->view<EntityPositionInterpolation, Transform>()
         .each([&](const auto entity, const EntityPositionInterpolation& interpolation, Transform& ts) {
             auto [from, to, value] = interpolation.get_values_around(time_point);
+            spdlog::info("From: {} {} {} - To: {} {} {} - By: {}", 
+                    from.x, from.y, from.z,
+                    to.x, to.y, to.z,
+                    value);
             ts.set_position(glm::mix(from, to, value));
         });
 }

modules/client/src/network/InterpolatedProperty.hpp

@@ -5,15 +5,21 @@
 
 #include "common.hpp"
 
-template<typename T, int length = 3>
+template<typename T, int length = 10>
 class InterpolatedProperty {
     using Clock = std::chrono::high_resolution_clock;
 
-    std::array<T, length> m_buffer;
-    std::array<Clock::time_point, length> m_time_buffer;
+    std::vector<T> m_buffer;
+    std::vector<Clock::time_point> m_time_buffer;
+
+    uint32_t m_head;
+    uint32_t m_size;
 
 public:
-    InterpolatedProperty(T initial_value) {
+    InterpolatedProperty(T initial_value) :
+        m_buffer(length),
+        m_time_buffer(length),
+        m_size(0), m_head(0) {
         for(int i = 0; i < length; i++) {
             m_buffer[i] = initial_value;
             m_time_buffer[i] = Clock::now();
@@ -23,7 +29,21 @@ public:
     GET_REF(m_buffer, values);
     GET_REF(m_time_buffer, times);
 
+    /** How many slots hold something that was pushed. */
+    inline uint32_t size() const {
+        return m_size;
+    }
+
     void push(Clock::time_point point, T value) {
+        // m_buffer[m_head] = std::move(value);
+        // m_time_buffer[m_head] = point;
+        //
+        // m_head = (m_head + 1) % m_buffer.size();
+        //
+        // if (m_size < m_buffer.size())
+        // {
+        //     ++m_size;
+        // }
         if(point < m_time_buffer.at(0)) {
             return;
         }
@@ -64,6 +84,46 @@ public:
     }
 
     inline std::tuple<T, T, float> get_values_around(Clock::time_point point) const {
+        /* const std::size_t capacity = m_buffer.size();
+        const std::size_t oldest = (m_head + capacity - m_size) % capacity;
+
+        if (m_size == 0)
+        {
+            return { T(), T(), 0.0f };
+        }
+
+        // Asking for a time the buffer no longer reaches back to. Standing on
+        // the oldest is wrong by however much was missed, but it is wrong in
+        // the direction the values were heading, unlike the newest.
+        if (point < m_time_buffer[oldest])
+        {
+            return { m_buffer[oldest], m_buffer[oldest], 0.0f };
+        }
+
+        for (std::size_t i = 0; i + 1 < m_size; ++i)
+        {
+            const std::size_t idx0 = (oldest + i) % capacity;
+            const std::size_t idx1 = (oldest + i + 1) % capacity;
+
+            const auto t0 = m_time_buffer[idx0];
+            const auto t1 = m_time_buffer[idx1];
+
+            if (point >= t0 && point <= t1)
+            {
+                const auto total =
+                    std::chrono::duration<float>(t1 - t0).count();
+                const auto elapsed =
+                    std::chrono::duration<float>(point - t0).count();
+
+                const float alpha = total > 0.0f ? elapsed / total : 0.0f;
+
+                return { m_buffer[idx0], m_buffer[idx1], alpha };
+            }
+        }
+
+        // Handle exact last sample (or clamp)
+        const std::size_t last = (oldest + m_size - 1) % capacity;
+        return { m_buffer[last], m_buffer[last], 0.0f }; */
         T prev = m_buffer.at(0);
         Clock::time_point prev_point = m_time_buffer.at(0);
 

modules/client/src/network/ReplicatorClient.cpp

@@ -151,6 +151,10 @@ void ReplicatorClient::handle_snapshot_entity(
             // return;
         }
 
+        // Applies correction from record_frame_idx to current_frame_idx (if any) on entity. Compares previous position on
+        // frame record_frame_idx with p
+        m_rollback.apply_correction(record_frame_idx, p, entity.value(), &m_world->registry(), current_frame_idx);
+
         //snap_player_to(current_frame_idx, entity.value(), p);
 
         // bool reconcile_happened = m_reconciler.reconcile(record_frame_idx, p, entity.value(), &m_world->registry(), current_frame_idx);
@@ -168,15 +172,29 @@ void ReplicatorClient::handle_snapshot_entity(
         //     }
         //     m_network_metrics->record_ack_lag(ack_lag);
         // }
-    } 
-
+    } else {
         m_entity_interpolator->set_position(std::chrono::high_resolution_clock::now(), entity.value(), p);
+    }
 }
 
 void ReplicatorClient::handle_snapshot(uint32_t current_frame_idx, serial::WorldStateReader& reader) {
     auto header = reader.read_header();
     measure_response_time(current_frame_idx, header.frame_idx);
 
+    // Snapshots are sent unreliably, so one can overtake another. Taking a
+    // late one would put entities back where they have already been seen.
+    if(header.tick_idx <= m_latest_tick_idx) {
+        return;
+    }
+
+    m_latest_tick_idx = header.tick_idx;
+
+    // Arrival is the only time the client can be sure of, and it grows with
+    // every snapshot, which is what reading the buffer back relies on. What it
+    // costs is spacing: the gaps between samples carry the jitter of the way
+    // here rather than the even gaps the server sent them on.
+    const auto taken_at = std::chrono::high_resolution_clock::now();
+
     while(reader.has_entity()) {
         auto entity_r = reader.read_entity();
 

modules/client/src/network/ReplicatorClient.hpp

@@ -86,6 +86,7 @@ private:
     net::PlayerRollback m_rollback;
     World *m_world;
     net::ServerConnection* m_server_connection;
+    uint32_t m_latest_tick_idx = 0;
 
     std::optional<entt::entity> m_player_entity;
 

modules/client/src/world/ThirdPersonPlayerController.cpp

@@ -50,7 +50,12 @@ void ThirdPersonPlayerController::update(const tw::io::InputManager* input, doub
     m_camera_rotation = yaw * m_camera_rotation * pitch;
 
     glm::vec3 offset = m_camera_rotation * glm::vec3(0, 0, m_camera_zoom);
-    m_camera->view().look_at(get_target_position() + offset, get_target_position());
+
+    glm::vec3 from = m_camera->view().position();
+    glm::vec3 to = get_target_position() + offset;
+    glm::vec3 interpolated = glm::mix(from, to, 0.8f);
+
+    m_camera->view().look_at(interpolated, get_target_position());
 }
 
 }

modules/client/src/world/controllers/ClientWorldController.cpp

@@ -25,8 +25,6 @@
 
 namespace tw {
 
-typedef  HistoryBuffer<long, glm::vec3> EntityPositionHistory;
-
 entt::entity
 ClientWorldController::create_entity(const std::string& name, glm::vec3 position) {
     const auto entity = m_world->registry().create();
@@ -82,8 +80,8 @@ void ClientWorldController::spawn_entity(const std::string& name, uint32_t serve
     if(m_controlled_server_id.has_value() && m_controlled_server_id.value() == server_id) {
         try_bind_player_entity();
     } else {
-    }
         m_interpolator.register_entity(entity);
+    }
 }
 
 ClientWorldController::ClientWorldController(
@@ -165,9 +163,9 @@ void ClientWorldController::try_bind_player_entity() {
         position
     ));
 
-    // if(m_world->registry().all_of<net::EntityPositionInterpolation>(entity)) {
-    //     m_world->registry().remove<net::EntityPositionInterpolation>(entity);
-    // }
+    if(m_world->registry().all_of<net::EntityPositionInterpolation>(entity)) {
+        m_world->registry().remove<net::EntityPositionInterpolation>(entity);
+    }
 }
 
 
@@ -187,7 +185,6 @@ void ClientWorldController::update_network() {
     });
    
 
-    m_replicator_client.record_prediction(m_frame_idx);
 
 
     // m_world->registry().view<Transform>()
@@ -216,10 +213,11 @@ void ClientWorldController::update(double delta_time) {
             if(controller) {
                 // controller->set_input(m_network_frame_idx, input);
                 m_replicator_client.set_input(m_network_frame_idx, input);
+                m_replicator_client.record_prediction(m_network_frame_idx);
             }
         }
 
-        // m_physics_world->step(m_network_frame_idx, JoltPhysicsWorld::FIXED_DELTA_TIME, true);
+        m_physics_world->step(m_network_frame_idx, JoltPhysicsWorld::FIXED_DELTA_TIME, true);
         m_network_frame_idx++;
     }
 
@@ -230,7 +228,7 @@ void ClientWorldController::update(double delta_time) {
         // TODO: The third person controller could pull
         Transform* player_transform = m_world->registry().try_get<Transform>(m_player_entity.value());
         if(player_transform) {
-            m_player_controller.set_target(player_transform->position());
+            // m_player_controller.set_target(player_transform->position());
         }
     }
 

modules/serialization/include/tw/serial/WorldStateWriter.hpp

@@ -23,7 +23,7 @@ class WorldStateWriter {
 public:
     explicit WorldStateWriter(BinaryBuffer& buf) noexcept : m_w(buf) {}
 
-    void begin(uint32_t frame_idx, uint32_t message_type) noexcept {
+    void begin(uint32_t frame_idx, uint32_t tick_idx, uint32_t message_type) noexcept {
         m_entity_count = 0;
 
         // message_type — lets the receiver dispatch without peeking further
@@ -35,6 +35,10 @@ public:
         // frame_idx
         m_w.encode<uint32_t>(frame_idx);
 
+        // tick_idx — counts the states that went out, so the receiver can tell
+        // a late one from a new one. Says nothing about the frame answered.
+        m_w.encode<uint32_t>(tick_idx);
+
         // entity_count placeholder — patched when end() is called
         m_entity_count_offset = m_w.reserve_u32();
     }
@@ -85,6 +89,7 @@ public:
 struct WorldStateHeader {
     uint32_t packet_type;
     uint32_t frame_idx;
+    uint32_t tick_idx;
     uint32_t entity_count;
 };
 
@@ -109,10 +114,11 @@ public:
     explicit WorldStateReader(std::span<const std::byte> data) noexcept
         : m_r(data) {}
 
-    /** Read the 12-byte header. Must be called first. */
+    /** Read the header. Must be called first. */
     WorldStateHeader read_header() noexcept {
         // m_header.packet_type  = m_r.decode<uint32_t>();
         m_header.frame_idx    = m_r.decode<uint32_t>();
+        m_header.tick_idx     = m_r.decode<uint32_t>();
         m_header.entity_count = m_r.decode<uint32_t>();
 
         // spawn count follows immediately

modules/server/src/ZoneServer.cpp

@@ -62,6 +62,9 @@ void ZoneServer::player_update_handler(SessionId session_id, mmo::PlayerMoveMess
     if (it == m_session_zone.end()) return;
 
     if (auto* session = m_player_session_registry->session(session_id)) {
+        if(session->last_received_frame >= message.frame_idx()) {
+            return;
+        }
         session->last_received_frame = message.frame_idx();
     }
 
@@ -141,7 +144,7 @@ void ZoneServer::run() {
                 }
             }
 
-            m_replicator->replicate(zone->registry(), zone->interest());
+            m_replicator->replicate(frame_idx, zone->registry(), zone->interest());
         }
 
         m_network_receiver->update();

modules/server/src/replication/StateReplicator.hpp

@@ -29,8 +29,8 @@ class StateReplicator {
     // Per-client backing buffers reused every frame.
     std::vector<tw::serial::BinaryBuffer> m_frames;
 
-    // Header(16) + spawn_hdr(4) + despawn_hdr(4) + 512 entities × 16 bytes
-    static constexpr std::size_t kHeaderCapacity  = 24;
+    // Header(20) + spawn_hdr(4) + despawn_hdr(4) + 512 entities × 16 bytes
+    static constexpr std::size_t kHeaderCapacity  = 28;
     static constexpr std::size_t kInitialCapacity = kHeaderCapacity + 512 * 16;
 
 public:
@@ -46,6 +46,7 @@ public:
      * Replicates the current world state for one zone to its connected clients.
      */
     void replicate(
+            uint32_t frame_idx,
             const entt::registry& registry,
             const im::InterestSystem<Backend>* interest_manager
     ) {
@@ -88,7 +89,8 @@ public:
 
                 m_frames[i].reserve(needed);
                 writers[i].reset();
-                writers[i].begin(session->last_received_frame, Message<mmo::WorldStateMessage>::value);
+                writers[i].begin(session->last_received_frame, frame_idx,
+                    Message<mmo::WorldStateMessage>::value);
                 writers[i].write_spawns(state->spawn());
                 writers[i].write_despawns(state->despawn());