feat(client-entity): use snapshot history for entity interpolation

Replace exponential smoothing with a buffered snapshot system. Each entity keeps a deque of position/direction snapshots with timestamps; the render transform is interpolated at a fixed 100 ms render delay to hide network jitter. Snapshots are capped to 16 entries.

include/Cubed/gameplay/client_entity_manager.hpp

@@ -1,6 +1,7 @@
 #pragma once
 #include "Cubed/gameplay/ecs/entity.hpp"
 #include "Cubed/gameplay/gait.hpp"
+#include "Cubed/tools/cubed_random.hpp"
 #include "glm/ext/vector_float3.hpp"
 #include "world/entity.pb.h"
 
@@ -26,6 +27,8 @@ public:
 
     const entt::registry& get_registry() const;
 
+    void player_sound(float dt);
+
 private:
     struct EntityCreateElement {
         EntityID id;
@@ -52,7 +55,7 @@ private:
     EntityMap m_entities;
     std::unordered_map<std::string_view, CreateFunc> m_factories;
     tbb::concurrent_queue<TaskPair> m_tasks;
-
+    Random m_random;
     void handle_task(float dt);
     void handle_entity_destory(EntityID id);
     // not thread safe

include/Cubed/gameplay/ecs/client_entity.hpp

@@ -2,6 +2,8 @@
 #include "Cubed/gameplay/ecs/animation.hpp"
 #include "Cubed/gameplay/ecs/transform.hpp"
 #include "Cubed/gameplay/model.hpp"
+
+#include <deque>
 namespace Cubed {
 struct BaseClientCreature {
 
@@ -11,4 +13,19 @@ struct BaseClientCreature {
 
     ModelID model;
 };
+
+struct SoundTime {
+    float next_call_time;
+};
+
+struct ClientEntitySnapshot {
+    double time_ms = 0.0;
+    glm::vec3 pos{0.0f};
+    glm::vec3 dir{0.0f};
+};
+
+struct ClientEntityState {
+    std::deque<ClientEntitySnapshot> history;
+};
+
 } // namespace Cubed

include/Cubed/tools/time_tools.hpp

@@ -4,6 +4,7 @@
 #include <cstdint>
 namespace Cubed {
 namespace Tools {
+// return ms
 inline uint64_t get_time_ticks() { return SDL_GetTicks(); }
 } // namespace Tools
 

src/gameplay/client_entity_manager.cpp

@@ -7,14 +7,76 @@
 #include "Cubed/gameplay/ecs/transform.hpp"
 #include "Cubed/render/model_manager.hpp"
 #include "Cubed/tools/cubed_assert.hpp"
+#include "Cubed/tools/math_tools.hpp"
 #include "Cubed/tools/net_utils.hpp"
-
+#include "Cubed/tools/time_tools.hpp"
 using namespace google::protobuf;
 
 namespace Cubed {
+
+namespace {
+constexpr double ENTITY_RENDER_DELAY_MS = 100.0; // two tick time
+constexpr size_t ENTITY_SNAPSHOT_MAX = 16;
+
+ClientEntitySnapshot
+interpolate_snapshot(const std::deque<ClientEntitySnapshot>& history,
+                     double render_time) {
+
+    if (history.empty()) {
+        return {};
+    }
+
+    if (history.size() == 1) {
+        return history.front();
+    }
+
+    auto upper = std::lower_bound(
+        history.begin(), history.end(), render_time,
+        [](const ClientEntitySnapshot& s, double t) { return s.time_ms < t; });
+
+    if (upper == history.end()) {
+        return history.back();
+    }
+
+    if (upper == history.begin()) {
+        return *upper;
+    }
+
+    auto lower = upper - 1;
+
+    double span = upper->time_ms - lower->time_ms;
+
+    float t = span > 0.0 ? float((render_time - lower->time_ms) / span) : 1.0f;
+
+    t = std::clamp(t, 0.0f, 1.0f);
+
+    ClientEntitySnapshot out;
+
+    out.pos = glm::mix(lower->pos, upper->pos, t);
+
+    glm::vec3 mixed = glm::mix(lower->dir, upper->dir, t);
+
+    out.dir =
+        glm::length(mixed) > 1e-6f ? glm::normalize(mixed) : glm::vec3{0.0f};
+    return out;
+}
+} // namespace
+
 ClientEntityManager::ClientEntityManager(ClientWorld& world) : m_world(world) {}
 void ClientEntityManager::update(float dt) {
     handle_task(dt);
+    {
+        auto view = m_registry.view<ClientEntityState, RenderTransform>();
+        double render_time = static_cast<double>(Tools::get_time_ticks()) -
+                             ENTITY_RENDER_DELAY_MS;
+        for (auto e : view) {
+            auto& state = view.get<ClientEntityState>(e);
+            auto& r = view.get<RenderTransform>(e);
+            auto snap = interpolate_snapshot(state.history, render_time);
+            r.position.value = snap.pos;
+            r.direction.value = snap.dir;
+        }
+    }
 
     auto view = m_registry.view<BaseClientCreature>();
     for (auto e : view) {
@@ -25,15 +87,20 @@ void ClientEntityManager::update(float dt) {
             c.pose.walk_time += dt;
         }
     }
+
+    player_sound(dt);
 }
 
 void ClientEntityManager::init() {
+    m_random.init(std::random_device()());
     m_factories.emplace("cubed:pig", [this](EntityID id) {
         BaseClientCreature c;
         c.model = ModelManager::instance().get_model_id("cubed:pig");
-        create_entity_in_registry(id, Entity{id, EntityType::CREATURE},
-                                  EntityInfo{"cubed:pig", ""}, std::move(c),
-                                  PigTag{}, RenderTransform{});
+        float next_call_time = m_random.random_float(8.0f, 25.0f);
+        create_entity_in_registry(
+            id, Entity{id, EntityType::CREATURE}, EntityInfo{"cubed:pig", ""},
+            std::move(c), PigTag{}, RenderTransform{},
+            SoundTime{next_call_time}, ClientEntityState{});
     });
 }
 // not thread safe
@@ -50,9 +117,13 @@ void ClientEntityManager::handle_entity_create(EntityID id,
     auto* r = m_registry.try_get<RenderTransform>(a->second);
     ASSERT(r);
     r->position.value = pos;
+    auto* s = m_registry.try_get<ClientEntityState>(a->second);
+    ASSERT(s);
+    s->history.emplace_back(static_cast<double>(Tools::get_time_ticks()), pos,
+                            glm::vec3{0, 0, 0});
 }
 
-void ClientEntityManager::handle_entity_update(UpdateInfo& info, float dt) {
+void ClientEntityManager::handle_entity_update(UpdateInfo& info, float) {
     entt::entity e;
     {
         cacc a;
@@ -67,13 +138,14 @@ void ClientEntityManager::handle_entity_update(UpdateInfo& info, float dt) {
     creature->transform.position.value = info.pos;
     creature->transform.direction.value = info.direction;
     creature->pose.gait = info.gait;
-    auto r = m_registry.try_get<RenderTransform>(e);
-    ASSERT(r);
-    float alpha = 1 - std::exp(-dt / 0.1);
-    r->direction.value = glm::mix(r->direction.value,
-                                  creature->transform.direction.value, alpha);
-    r->position.value =
-        glm::mix(r->position.value, creature->transform.position.value, alpha);
+
+    auto state = m_registry.try_get<ClientEntityState>(e);
+    ASSERT(state);
+    state->history.push_back({static_cast<double>(Tools::get_time_ticks()),
+                              info.pos, info.direction});
+    while (state->history.size() > ENTITY_SNAPSHOT_MAX) {
+        state->history.pop_front();
+    }
 }
 
 void ClientEntityManager::receive_entity_create(S2CEntityCreate& s2c) {
@@ -157,4 +229,27 @@ void ClientEntityManager::handle_entity_destory(EntityID id) {
 const entt::registry& ClientEntityManager::get_registry() const {
     return m_registry;
 }
+
+void ClientEntityManager::player_sound(float dt) {
+    auto& audio = m_world.get_audio();
+    auto player_pos = m_world.player_manager().get_local().get_player_pos();
+    auto view = m_registry.view<EntityInfo, BaseClientCreature, SoundTime>();
+
+    for (auto e : view) {
+        const auto [info, creature] =
+            view.get<EntityInfo, BaseClientCreature>(e);
+        if (Math::distance2(player_pos, creature.transform.position.value) >
+            10 * 10) {
+            continue;
+        }
+        auto& sound_time = view.get<SoundTime>(e);
+        sound_time.next_call_time -= dt;
+        if (sound_time.next_call_time <= 0.0f) {
+            audio.play_3d("creature/pig/call.mp3",
+                          creature.transform.position.value);
+            sound_time.next_call_time = m_random.random_float(8.0f, 25.0f);
+        }
+    }
+}
+
 } // namespace Cubed