diff --git a/CMakeLists.txt b/CMakeLists.txt
index d2baa48..636e427 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -7,6 +7,8 @@ add_library(boundard STATIC
     src/game.cpp
     src/scene.cpp
     src/render.cpp
+    src/render_loop.cpp
+    src/input.cpp
     src/config.cpp
     src/engine.cpp
 )
diff --git a/examples/square/config.ceg b/examples/square/config.ceg
index 2f99edf..2529ece 100644
--- a/examples/square/config.ceg
+++ b/examples/square/config.ceg
@@ -8,10 +8,10 @@
     "input": [
         { "action": "quit", "keys": ["Escape"] },
         { "action": "switch_scene", "keys": ["Tab"] },
-        { "action": "move_left", "keys": ["Left"] },
-        { "action": "move_right", "keys": ["Right"] },
-        { "action": "move_up", "keys": ["Up"] },
-        { "action": "move_down", "keys": ["Down"] }
+        { "action": "move_left", "keys": ["a"] },
+        { "action": "move_right", "keys": ["d"] },
+        { "action": "move_up", "keys": ["w"] },
+        { "action": "move_down", "keys": ["s"] }
     ],
 
     "start_scene": "square",
diff --git a/examples/square/main.cpp b/examples/square/main.cpp
index ee0ae0d..ba85d05 100644
--- a/examples/square/main.cpp
+++ b/examples/square/main.cpp
@@ -19,10 +19,6 @@ void register_square_behaviors() {
         "square_tick",
         [](boundard::Actor& actor, float dt, const boundard::render::InputMap& input) {
             const float t = actor.age();
-            actor.set_facing({
-                std::cos(t * 1.5F),
-                std::sin(t * 1.5F),
-            });
 
             if (actor.mesh() != nullptr) {
                 actor.mesh()->set_color({
@@ -34,7 +30,7 @@ void register_square_behaviors() {
             }
 
             auto position = actor.position();
-            const float move_speed = 0.7F;
+            constexpr float move_speed = 0.7F;
             position[0] += input.get_axis("move_left", "move_right") * move_speed * dt;
             position[1] += input.get_axis("move_up", "move_down") * move_speed * dt;
             actor.set_position(position);
@@ -54,12 +50,8 @@ void register_square_behaviors() {
 
     behaviors.register_tick(
         "square_alt_tick",
-        [](boundard::Actor& actor, float dt, const boundard::render::InputMap& input) {
+        [](boundard::Actor& actor, const float dt, const boundard::render::InputMap& input) {
             const float t = actor.age();
-            actor.set_facing({
-                std::sin(t * 1.3F),
-                std::cos(t * 1.3F),
-            });
 
             if (actor.mesh() != nullptr) {
                 actor.mesh()->set_color({
@@ -71,7 +63,7 @@ void register_square_behaviors() {
             }
 
             auto position = actor.position();
-            const float move_speed = 0.7F;
+            constexpr float move_speed = 0.7F;
             position[0] += input.get_axis("move_left", "move_right") * move_speed * dt;
             position[1] += input.get_axis("move_up", "move_down") * move_speed * dt;
             actor.set_position(position);
diff --git a/examples/square/scenes/square.json b/examples/square/scenes/square.json
index 1d70b83..b142f6a 100644
--- a/examples/square/scenes/square.json
+++ b/examples/square/scenes/square.json
@@ -1,21 +1,31 @@
 {
-  "actors": [
-    {
-      "name": "square",
-      "init": "square_init",
-      "tick": "square_tick",
-      "position": {
-        "x": 0,
-        "y": 0
-      },
-      "facing": {
-        "x": 1,
-        "y": 0
-      },
-      "mesh": {
-        "shape": "quad",
-        "texture": "Dank.png"
-      }
-    }
-  ]
+    "default_camera": "square_camera",
+    "grid_background": true,
+    "actors": [
+        {
+            "name": "square",
+            "init": "square_init",
+            "tick": "square_tick",
+            "position": {
+                "x": 0,
+                "y": 0
+            },
+            "facing": {
+                "x": 1,
+                "y": 0
+            },
+            "mesh": {
+                "shape": "quad",
+                "texture": "Dank.png"
+            },
+            "children": [
+                {
+                    "name": "square_camera",
+                    "type": "camera",
+                    "position": { "x": 0, "y": 0 },
+                    "zoom": 0.2
+                }
+            ]
+        }
+    ]
 }
diff --git a/examples/square/scenes/square_alt.json b/examples/square/scenes/square_alt.json
index e3c5189..29027a1 100644
--- a/examples/square/scenes/square_alt.json
+++ b/examples/square/scenes/square_alt.json
@@ -1,4 +1,6 @@
 {
+    "default_camera": "square_alt_camera",
+    "grid_background": true,
     "actors": [
         {
             "name": "square_alt",
@@ -9,7 +11,15 @@
             "mesh": {
                 "shape": "quad",
                 "color": { "r": 0.9, "g": 0.3, "b": 0.2, "a": 1.0 }
-            }
+            },
+            "children": [
+                {
+                    "name": "square_alt_camera",
+                    "type": "camera",
+                    "position": { "x": 0, "y": 0 },
+                    "zoom": 1.0
+                }
+            ]
         }
     ]
 }
diff --git a/include/actor.hpp b/include/actor.hpp
index 5b852a4..4db1112 100644
--- a/include/actor.hpp
+++ b/include/actor.hpp
@@ -5,6 +5,7 @@
 #include <memory>
 #include <mutex>
 #include <string>
+#include <vector>
 
 #include <game.hpp>
 #include <mesh.hpp>
@@ -15,14 +16,16 @@ class InputMap;
 
 namespace boundard {
 
-class Actor {
+class Actor : public std::enable_shared_from_this<Actor> {
    private:
     size_t id;
     std::string nickName_;
     mutable std::mutex transform_mutex_;
     std::array<float, 2> position_{0.0F, 0.0F};
     std::array<float, 2> facing_{1.0F, 0.0F};
-    std::shared_ptr<Mesh> mesh_;
+    mutable std::mutex tree_mutex_;
+    std::weak_ptr<Actor> parent_;
+    std::vector<std::shared_ptr<Actor>> children_;
 
     float age_ = 0.0F;
     bool initialized_ = false;
@@ -43,11 +46,6 @@ class Actor {
         nickName_ = std::move(nickName);
     }
 
-    Actor(std::string nickName, Game& game, std::shared_ptr<Mesh> mesh)
-        : Actor(std::move(nickName), game) {
-        mesh_ = std::move(mesh);
-    }
-
     static Actor& getInstance() {
         static Actor instance;
         return instance;
@@ -75,6 +73,9 @@ class Actor {
         if (init_handler_) {
             init_handler_(*this);
         }
+        for (const std::shared_ptr<Actor>& child : children()) {
+            child->initialize();
+        }
     }
 
     // 类似 Godot 的 _process(delta)。
@@ -83,6 +84,9 @@ class Actor {
         if (tick_handler_) {
             tick_handler_(*this, dt, input);
         }
+        for (const std::shared_ptr<Actor>& child : children()) {
+            child->process(dt, input);
+        }
     }
 
     std::array<float, 2> position() const {
@@ -95,6 +99,19 @@ class Actor {
         position_ = position;
     }
 
+    std::array<float, 2> global_position() const {
+        const std::array<float, 2> local_position = position();
+        const std::shared_ptr<Actor> parent = this->parent();
+        if (parent == nullptr) return local_position;
+
+        const std::array<float, 2> parent_position = parent->global_position();
+        const std::array<float, 2> parent_facing = parent->global_facing();
+        return {parent_position[0] + parent_facing[0] * local_position[0] -
+                    parent_facing[1] * local_position[1],
+                parent_position[1] + parent_facing[1] * local_position[0] +
+                    parent_facing[0] * local_position[1]};
+    }
+
     std::array<float, 2> facing() const {
         std::lock_guard<std::mutex> lock(transform_mutex_);
         return facing_;
@@ -105,8 +122,67 @@ class Actor {
         facing_ = facing;
     }
 
-    const std::shared_ptr<Mesh>& mesh() const { return mesh_; }
-    void set_mesh(std::shared_ptr<Mesh> mesh) { mesh_ = std::move(mesh); }
+    std::array<float, 2> global_facing() const {
+        std::array<float, 2> local_facing = facing();
+        const std::shared_ptr<Actor> parent = this->parent();
+        if (parent == nullptr) return local_facing;
+
+        const std::array<float, 2> parent_facing = parent->global_facing();
+        return {parent_facing[0] * local_facing[0] - parent_facing[1] * local_facing[1],
+                parent_facing[1] * local_facing[0] + parent_facing[0] * local_facing[1]};
+    }
+
+    virtual const std::shared_ptr<Mesh>& mesh() const {
+        static const std::shared_ptr<Mesh> no_mesh;
+        return no_mesh;
+    }
+    virtual void set_mesh(std::shared_ptr<Mesh>) {}
+
+    std::shared_ptr<Actor> parent() const {
+        std::lock_guard<std::mutex> lock(tree_mutex_);
+        return parent_.lock();
+    }
+
+    std::vector<std::shared_ptr<Actor>> children() const {
+        std::lock_guard<std::mutex> lock(tree_mutex_);
+        return children_;
+    }
+
+    bool add_child(const std::shared_ptr<Actor>& child) {
+        if (child == nullptr) return false;
+        const std::shared_ptr<Actor> self = shared_from_this();
+        if (child == self) return false;
+        for (std::shared_ptr<Actor> ancestor = self; ancestor != nullptr;
+             ancestor = ancestor->parent()) {
+            if (ancestor == child) return false;
+        }
+
+        if (const std::shared_ptr<Actor> old_parent = child->parent()) {
+            old_parent->remove_child(child);
+        }
+        {
+            std::lock_guard<std::mutex> lock(tree_mutex_);
+            children_.push_back(child);
+        }
+        {
+            std::lock_guard<std::mutex> lock(child->tree_mutex_);
+            child->parent_ = self;
+        }
+        return true;
+    }
+
+    bool remove_child(const std::shared_ptr<Actor>& child) {
+        if (child == nullptr) return false;
+        std::lock_guard<std::mutex> lock(tree_mutex_);
+        for (auto it = children_.begin(); it != children_.end(); ++it) {
+            if (*it != child) continue;
+            children_.erase(it);
+            std::lock_guard<std::mutex> child_lock(child->tree_mutex_);
+            child->parent_.reset();
+            return true;
+        }
+        return false;
+    }
 };
 
 }  // namespace boundard
diff --git a/include/boundard.hpp b/include/boundard.hpp
index db879cf..b9df25d 100644
--- a/include/boundard.hpp
+++ b/include/boundard.hpp
@@ -3,6 +3,8 @@
 #include <game.hpp>
 #include <mesh.hpp>
 #include <actor.hpp>
+#include <sprite_actor.hpp>
+#include <camera.hpp>
 #include <behavior.hpp>
 #include <render.hpp>
 #include <config.hpp>
diff --git a/include/camera.hpp b/include/camera.hpp
new file mode 100644
index 0000000..2a2165c
--- /dev/null
+++ b/include/camera.hpp
@@ -0,0 +1,20 @@
+#pragma once
+
+#include <string>
+
+#include <actor.hpp>
+
+namespace boundard {
+
+class Camera : public Actor {
+   public:
+    Camera(std::string name, Game& game) : Actor(std::move(name), game) {}
+
+    float zoom() const { return zoom_; }
+    void set_zoom(float zoom) { zoom_ = zoom > 0.0F ? zoom : 0.0001F; }
+
+   private:
+    float zoom_ = 1.0F;
+};
+
+}  // namespace boundard
diff --git a/include/config.hpp b/include/config.hpp
index eb6e75a..3427cc8 100644
--- a/include/config.hpp
+++ b/include/config.hpp
@@ -21,11 +21,14 @@ struct MeshConfig {
 
 struct ActorConfig {
     std::string name;
+    std::string type = "actor";
     std::string init_function;
     std::string tick_function;
     std::array<float, 2> position{0.0F, 0.0F};
     std::array<float, 2> facing{1.0F, 0.0F};
+    float zoom = 1.0F;
     MeshConfig mesh;
+    std::vector<ActorConfig> children;
 };
 
 struct InputBindingConfig {
@@ -38,6 +41,8 @@ struct SceneConfig {
     std::string name;
     std::string path;
     std::vector<ActorConfig> actors;
+    std::string default_camera;
+    bool grid_background = false;
 };
 
 struct GameConfig {
diff --git a/include/mesh.hpp b/include/mesh.hpp
index 341c632..77fbcc8 100644
--- a/include/mesh.hpp
+++ b/include/mesh.hpp
@@ -44,6 +44,33 @@ class Mesh {
         return mesh;
     }
 
+    static Mesh grid(int half_cells = 12) {
+        Mesh mesh;
+        const float world_to_local = 1.0F / 0.35F;
+        const float half_extent = static_cast<float>(half_cells) * world_to_local;
+        const float line_half_width = 0.012F * world_to_local;
+        const std::array<float, 4> line_color{1.0F, 1.0F, 1.0F, 1.0F};
+        auto add_rect = [&](float left, float bottom, float right, float top) {
+            const uint32_t base = static_cast<uint32_t>(mesh.vertices.size());
+            mesh.vertices.insert(mesh.vertices.end(), {
+                {{left, bottom}, line_color, {0.0F, 0.0F}},
+                {{right, bottom}, line_color, {1.0F, 0.0F}},
+                {{right, top}, line_color, {1.0F, 1.0F}},
+                {{left, top}, line_color, {0.0F, 1.0F}},
+            });
+            mesh.indices.insert(mesh.indices.end(),
+                                {base, base + 1, base + 2, base + 2, base + 3, base});
+        };
+        for (int cell = -half_cells; cell <= half_cells; ++cell) {
+            const float coordinate = static_cast<float>(cell) * world_to_local;
+            add_rect(coordinate - line_half_width, -half_extent, coordinate + line_half_width,
+                     half_extent);
+            add_rect(-half_extent, coordinate - line_half_width, half_extent,
+                     coordinate + line_half_width);
+        }
+        return mesh;
+    }
+
    private:
     std::unique_ptr<std::mutex> color_mutex_ = std::make_unique<std::mutex>();
     std::array<float, 4> color_{1.0F, 1.0F, 1.0F, 1.0F};
diff --git a/include/render.hpp b/include/render.hpp
index 5510f09..6e3d35b 100644
--- a/include/render.hpp
+++ b/include/render.hpp
@@ -13,6 +13,10 @@
 
 #include <actor.hpp>
 
+namespace boundard {
+class Camera;
+}
+
 namespace boundard::render {
 
 struct InputEvent {
@@ -51,6 +55,7 @@ class Renderer {
 
     void init(int width, int height, const char* title);
     void draw(const Actor* const* actors, size_t actor_count);
+    void draw(const Actor* const* actors, size_t actor_count, const Camera* camera);
     bool should_close() const;
     void poll_events() const;
 
@@ -119,6 +124,7 @@ class RenderLoop {
     void stop();
 
     void set_actors(std::vector<Actor*> actors);
+    void set_camera(Camera* camera);
     void poll_events() const;
     bool should_close() const;
 
@@ -134,6 +140,7 @@ class RenderLoop {
     std::atomic<bool> running_{false};
     mutable std::mutex actors_mutex_;
     std::vector<Actor*> actors_;
+    Camera* camera_ = nullptr;
 };
 
 }  // namespace boundard::render
diff --git a/include/scene.hpp b/include/scene.hpp
index 79bcd94..364a3c1 100644
--- a/include/scene.hpp
+++ b/include/scene.hpp
@@ -11,6 +11,7 @@ class InputMap;
 namespace boundard {
 
 class Actor;
+class Camera;
 
 // 运行时场景：持有场景名和其中的 Actor，并统一驱动 Actor 的 init/tick。
 class Scene {
@@ -30,6 +31,9 @@ class Scene {
     void set_actors(std::vector<std::shared_ptr<Actor>> actors);
     void clear();
 
+    void set_default_camera(std::string name);
+    Camera* primary_camera() const;
+
     const std::vector<Actor*>& actors() const;
     std::vector<Actor*>& actors();
 
@@ -39,7 +43,8 @@ class Scene {
    private:
     std::string name_;
     std::vector<std::shared_ptr<Actor>> actor_storage_;
-    std::vector<Actor*> actors_;
+    mutable std::vector<Actor*> actors_;
+    std::string default_camera_;
 };
 
 }  // namespace boundard
diff --git a/include/sprite_actor.hpp b/include/sprite_actor.hpp
new file mode 100644
index 0000000..95a525f
--- /dev/null
+++ b/include/sprite_actor.hpp
@@ -0,0 +1,21 @@
+#pragma once
+
+#include <string>
+
+#include <actor.hpp>
+
+namespace boundard {
+
+class SpriteActor : public Actor {
+   public:
+    SpriteActor(std::string name, Game& game, std::shared_ptr<Mesh> mesh)
+        : Actor(std::move(name), game), mesh_(std::move(mesh)) {}
+
+    const std::shared_ptr<Mesh>& mesh() const override { return mesh_; }
+    void set_mesh(std::shared_ptr<Mesh> mesh) override { mesh_ = std::move(mesh); }
+
+   private:
+    std::shared_ptr<Mesh> mesh_;
+};
+
+}  // namespace boundard
diff --git a/scenes/main.json b/scenes/main.json
index 0188937..e57a85e 100644
--- a/scenes/main.json
+++ b/scenes/main.json
@@ -1,4 +1,6 @@
 {
+    "default_camera": "main_camera",
+    "grid_background": true,
     "actors": [
         {
             "name": "square",
@@ -13,7 +15,16 @@
             "mesh": {
                 "shape": "quad",
                 "texture": "Dank.png"
-            }
+            },
+            "children": [
+                {
+                    "name": "main_camera",
+                    "type": "camera",
+                    "position": { "x": 0, "y": 0 },
+                    "facing": { "x": 1, "y": 0 },
+                    "zoom": 1.0
+                }
+            ]
         }
     ]
 }
diff --git a/src/config.cpp b/src/config.cpp
index 6dc5975..f61aeee 100644
--- a/src/config.cpp
+++ b/src/config.cpp
@@ -243,6 +243,9 @@ ActorConfig parse_actor(const Json::Value& value) {
     if (value.isMember("name")) {
         actor.name = json_string(value["name"], "");
     }
+    if (value.isMember("type")) {
+        actor.type = json_string(value["type"], actor.type);
+    }
     if (value.isMember("init")) {
         actor.init_function = json_string(value["init"], "");
     }
@@ -261,6 +264,9 @@ ActorConfig parse_actor(const Json::Value& value) {
         actor.facing[0] = json_float(facing["x"], actor.facing[0]);
         actor.facing[1] = json_float(facing["y"], actor.facing[1]);
     }
+    if (value.isMember("zoom")) {
+        actor.zoom = json_float(value["zoom"], actor.zoom);
+    }
 
     if (value.isMember("mesh") && value["mesh"].isObject()) {
         const Json::Value& mesh = value["mesh"];
@@ -272,6 +278,11 @@ ActorConfig parse_actor(const Json::Value& value) {
         }
         parse_color(mesh, actor.mesh);
     }
+    if (value.isMember("children") && value["children"].isArray()) {
+        for (const Json::Value& child : value["children"]) {
+            if (child.isObject()) actor.children.push_back(parse_actor(child));
+        }
+    }
 
     return actor;
 }
@@ -312,11 +323,13 @@ void extract_actors(const Json::Value& root, std::vector<ActorConfig>& actors) {
 void resolve_texture_paths(std::vector<ActorConfig>& actors,
                            const std::filesystem::path& base_dir) {
     for (ActorConfig& actor : actors) {
-        if (actor.mesh.texture.empty()) continue;
-        std::filesystem::path texture_path(actor.mesh.texture);
-        if (texture_path.is_relative()) {
-            actor.mesh.texture = (base_dir / texture_path).lexically_normal().string();
+        if (!actor.mesh.texture.empty()) {
+            std::filesystem::path texture_path(actor.mesh.texture);
+            if (texture_path.is_relative()) {
+                actor.mesh.texture = (base_dir / texture_path).lexically_normal().string();
+            }
         }
+        resolve_texture_paths(actor.children, base_dir);
     }
 }
 
@@ -330,6 +343,14 @@ bool parse_scene_entry(const Json::Value& item, SceneConfig& scene,
     if (item.isMember("name")) {
         scene.name = json_string(item["name"], "");
     }
+    if (item.isMember("default_camera")) {
+        scene.default_camera = json_string(item["default_camera"], "");
+    } else if (item.isMember("camera")) {
+        scene.default_camera = json_string(item["camera"], "");
+    }
+    if (item.isMember("grid_background")) {
+        scene.grid_background = item["grid_background"].asBool();
+    }
     if (scene.name.empty()) {
         error = "场景缺少 name";
         return false;
@@ -353,6 +374,14 @@ bool parse_scene_entry(const Json::Value& item, SceneConfig& scene,
             return false;
         }
         extract_actors(root, scene.actors);
+        if (root.isMember("default_camera")) {
+            scene.default_camera = json_string(root["default_camera"], scene.default_camera);
+        } else if (root.isMember("camera")) {
+            scene.default_camera = json_string(root["camera"], scene.default_camera);
+        }
+        if (root.isMember("grid_background")) {
+            scene.grid_background = root["grid_background"].asBool();
+        }
         resolve_texture_paths(scene.actors, scene_path.parent_path());
     } else {
         // 允许场景直接内联在游戏配置中。
diff --git a/src/engine.cpp b/src/engine.cpp
index 689111c..0a64cbe 100644
--- a/src/engine.cpp
+++ b/src/engine.cpp
@@ -8,6 +8,8 @@
 #include <vector>
 
 #include <boundard.hpp>
+#include <camera.hpp>
+#include <sprite_actor.hpp>
 
 namespace boundard {
 namespace {
@@ -24,9 +26,21 @@ std::shared_ptr<Actor> create_actor(const ActorConfig& actor_config, Game& game,
     mesh->set_color(actor_config.mesh.color);
     mesh->texture = actor_config.mesh.texture;
 
-    auto actor = std::make_shared<Actor>(actor_config.name, game, mesh);
+    std::shared_ptr<Actor> actor;
+    if (actor_config.type == "camera") {
+        actor = std::make_shared<Camera>(actor_config.name, game);
+    } else {
+        actor = std::make_shared<SpriteActor>(actor_config.name, game, mesh);
+    }
     actor->set_position(actor_config.position);
     actor->set_facing(actor_config.facing);
+    if (auto* camera = dynamic_cast<Camera*>(actor.get())) {
+        camera->set_zoom(actor_config.zoom);
+    }
+
+    for (const ActorConfig& child_config : actor_config.children) {
+        actor->add_child(create_actor(child_config, game, behaviors));
+    }
 
     if (!actor_config.init_function.empty()) {
         auto handler = behaviors.init(actor_config.init_function);
@@ -55,10 +69,18 @@ std::shared_ptr<Scene> build_scene(const SceneConfig& scene, Game& game,
                                    BehaviorRegistry& behaviors) {
     auto runtime_scene = std::make_shared<Scene>(scene.name);
 
+    if (scene.grid_background) {
+        auto grid = std::make_shared<SpriteActor>("__grid", game,
+                                                  std::make_shared<Mesh>(Mesh::grid()));
+        grid->mesh()->set_color({0.20F, 0.28F, 0.36F, 0.75F});
+        runtime_scene->add_actor(std::move(grid));
+    }
+
     for (const ActorConfig& actor_config : scene.actors) {
         auto actor = create_actor(actor_config, game, behaviors);
         runtime_scene->add_actor(std::move(actor));
     }
+    runtime_scene->set_default_camera(scene.default_camera);
 
     return runtime_scene;
 }
@@ -143,6 +165,7 @@ int run_engine(int argc, char** argv, const char* default_config_path) {
         scene->initialize();
         game.set_current_scene(scene);
         render_loop.set_actors(scene->actors());
+        render_loop.set_camera(scene->primary_camera());
     };
 
     if (active_scene != nullptr) {
diff --git a/src/input.cpp b/src/input.cpp
new file mode 100644
index 0000000..0ba5ac4
--- /dev/null
+++ b/src/input.cpp
@@ -0,0 +1,139 @@
+#include <render.hpp>
+
+namespace boundard::render {
+
+void InputMap::add_action(const std::string& action) {
+    std::lock_guard<std::mutex> lock(mutex_);
+    actions_.try_emplace(action);
+}
+
+void InputMap::bind_key(const std::string& action, int key) {
+    std::lock_guard<std::mutex> lock(mutex_);
+    ActionState& state = actions_[action];
+    state.keys.insert(key);
+    state.held_keys.try_emplace(key, false);
+}
+
+void InputMap::unbind_key(const std::string& action, int key) {
+    std::lock_guard<std::mutex> lock(mutex_);
+    auto action_it = actions_.find(action);
+    if (action_it == actions_.end()) return;
+    ActionState& state = action_it->second;
+    state.keys.erase(key);
+    auto held_it = state.held_keys.find(key);
+    if (held_it != state.held_keys.end() && held_it->second) {
+        held_it->second = false;
+        if (state.held_key_count > 0) --state.held_key_count;
+        if (state.held_key_count + state.held_button_count == 0) {
+            state.pressed = false;
+            state.just_released = true;
+        }
+    }
+    state.held_keys.erase(key);
+}
+
+void InputMap::bind_mouse_button(const std::string& action, int button) {
+    std::lock_guard<std::mutex> lock(mutex_);
+    ActionState& state = actions_[action];
+    state.mouse_buttons.insert(button);
+    state.held_buttons.try_emplace(button, false);
+}
+
+void InputMap::unbind_mouse_button(const std::string& action, int button) {
+    std::lock_guard<std::mutex> lock(mutex_);
+    auto action_it = actions_.find(action);
+    if (action_it == actions_.end()) return;
+    ActionState& state = action_it->second;
+    state.mouse_buttons.erase(button);
+    auto held_it = state.held_buttons.find(button);
+    if (held_it != state.held_buttons.end() && held_it->second) {
+        held_it->second = false;
+        if (state.held_button_count > 0) --state.held_button_count;
+        if (state.held_key_count + state.held_button_count == 0) {
+            state.pressed = false;
+            state.just_released = true;
+        }
+    }
+    state.held_buttons.erase(button);
+}
+
+void InputMap::handle_event(const InputEvent& event) {
+    std::lock_guard<std::mutex> lock(mutex_);
+    for (auto& [action, state] : actions_) {
+        std::unordered_set<int>* bindings = nullptr;
+        std::unordered_map<int, bool>* held_map = nullptr;
+        size_t* held_count = nullptr;
+        if (event.type == InputEvent::Type::Key) {
+            bindings = &state.keys;
+            held_map = &state.held_keys;
+            held_count = &state.held_key_count;
+        } else if (event.type == InputEvent::Type::MouseButton) {
+            bindings = &state.mouse_buttons;
+            held_map = &state.held_buttons;
+            held_count = &state.held_button_count;
+        } else {
+            continue;
+        }
+        const int input_id = event.type == InputEvent::Type::Key ? event.key : event.button;
+        if (bindings->find(input_id) == bindings->end()) continue;
+        if (event.action == InputEvent::Action::Press) {
+            bool& held = (*held_map)[input_id];
+            if (!held) {
+                held = true;
+                ++(*held_count);
+                if (state.held_key_count + state.held_button_count == 1) {
+                    state.pressed = true;
+                    state.just_pressed = true;
+                }
+            }
+        } else if (event.action == InputEvent::Action::Release) {
+            auto held_it = held_map->find(input_id);
+            if (held_it == held_map->end() || !held_it->second) continue;
+            held_it->second = false;
+            if (*held_count > 0) --(*held_count);
+            if (state.held_key_count + state.held_button_count == 0) {
+                state.pressed = false;
+                state.just_released = true;
+            }
+        }
+    }
+}
+
+void InputMap::end_frame() {
+    std::lock_guard<std::mutex> lock(mutex_);
+    for (auto& [action, state] : actions_) {
+        state.just_pressed = false;
+        state.just_released = false;
+    }
+}
+
+bool InputMap::is_action_pressed(const std::string& action) const {
+    std::lock_guard<std::mutex> lock(mutex_);
+    auto it = actions_.find(action);
+    return it != actions_.end() && it->second.pressed;
+}
+
+bool InputMap::is_action_just_pressed(const std::string& action) const {
+    std::lock_guard<std::mutex> lock(mutex_);
+    auto it = actions_.find(action);
+    return it != actions_.end() && it->second.just_pressed;
+}
+
+bool InputMap::is_action_just_released(const std::string& action) const {
+    std::lock_guard<std::mutex> lock(mutex_);
+    auto it = actions_.find(action);
+    return it != actions_.end() && it->second.just_released;
+}
+
+float InputMap::get_action_strength(const std::string& action) const {
+    std::lock_guard<std::mutex> lock(mutex_);
+    auto it = actions_.find(action);
+    return it != actions_.end() && it->second.pressed ? 1.0F : 0.0F;
+}
+
+float InputMap::get_axis(const std::string& negative_action,
+                         const std::string& positive_action) const {
+    return get_action_strength(positive_action) - get_action_strength(negative_action);
+}
+
+}  // namespace boundard::render
diff --git a/src/render.cpp b/src/render.cpp
index 1633c0f..a91774b 100644
--- a/src/render.cpp
+++ b/src/render.cpp
@@ -1,4 +1,5 @@
 #include <render.hpp>
+#include <camera.hpp>
 
 #define GLFW_INCLUDE_VULKAN
 #include <GLFW/glfw3.h>
@@ -197,6 +198,7 @@ struct Renderer::Impl {
     VkDescriptorPool descriptor_pool = VK_NULL_HANDLE;
     VkPipelineLayout pipeline_layout = VK_NULL_HANDLE;
     VkPipeline pipeline = VK_NULL_HANDLE;
+    std::atomic<bool> framebuffer_resized{false};
 
     VkCommandPool command_pool = VK_NULL_HANDLE;
     std::vector<FrameData> frames;
@@ -221,11 +223,12 @@ struct Renderer::Impl {
     Renderer::InputCallback input_callback;
 
     void init(int width, int height, const char* title);
-    void draw(const Actor* const* actors, size_t actor_count);
+    void draw(const Actor* const* actors, size_t actor_count, const Camera* camera);
     void upload_mesh(const Mesh& mesh);
     void create_texture(MeshResource& resource, const std::string& path);
     VkCommandBuffer begin_transfer();
     void end_transfer(VkCommandBuffer command_buffer);
+    void recreate_swapchain();
     void destroy();
 };
 
@@ -240,7 +243,11 @@ void Renderer::init(int width, int height, const char* title) {
 }
 
 void Renderer::draw(const Actor* const* actors, size_t actor_count) {
-    impl_->draw(actors, actor_count);
+    impl_->draw(actors, actor_count, nullptr);
+}
+
+void Renderer::draw(const Actor* const* actors, size_t actor_count, const Camera* camera) {
+    impl_->draw(actors, actor_count, camera);
 }
 
 bool Renderer::should_close() const {
@@ -277,6 +284,7 @@ void Renderer::destroy() {
     impl_->destroy();
 }
 
+#if 0  // InputMap implementation moved to input.cpp.
 void InputMap::add_action(const std::string& action) {
     std::lock_guard<std::mutex> lock(mutex_);
     actions_.try_emplace(action);
@@ -428,72 +436,7 @@ float InputMap::get_axis(const std::string& negative_action,
                          const std::string& positive_action) const {
     return get_action_strength(positive_action) - get_action_strength(negative_action);
 }
-
-RenderLoop::~RenderLoop() {
-    stop();
-}
-
-void RenderLoop::start(int width, int height, const char* title) {
-    if (running_) {
-        return;
-    }
-
-    renderer_.init(width, height, title);
-    renderer_.set_input_callback([this](const InputEvent& event) {
-        input_map_.handle_event(event);
-    });
-
-    running_ = true;
-    thread_ = std::thread(&RenderLoop::run, this);
-}
-
-void RenderLoop::stop() {
-    if (!running_) {
-        return;
-    }
-    running_ = false;
-    if (thread_.joinable()) {
-        thread_.join();
-    }
-    renderer_.destroy();
-}
-
-void RenderLoop::set_actors(std::vector<Actor*> actors) {
-    std::lock_guard<std::mutex> lock(actors_mutex_);
-    actors_ = std::move(actors);
-}
-
-void RenderLoop::poll_events() const {
-    renderer_.poll_events();
-}
-
-bool RenderLoop::should_close() const {
-    return renderer_.should_close();
-}
-
-InputMap& RenderLoop::input() {
-    return input_map_;
-}
-
-const InputMap& RenderLoop::input() const {
-    return input_map_;
-}
-
-void RenderLoop::run() {
-    while (running_) {
-        std::vector<Actor*> actors;
-        {
-            std::lock_guard<std::mutex> lock(actors_mutex_);
-            actors = actors_;
-        }
-
-        if (!actors.empty()) {
-            renderer_.draw(actors.data(), actors.size());
-        } else {
-            std::this_thread::yield();
-        }
-    }
-}
+#endif
 
 void Renderer::Impl::init(int width, int height, const char* title) {
     if (initialized) {
@@ -509,8 +452,11 @@ void Renderer::Impl::init(int width, int height, const char* title) {
     if (window == nullptr) {
         throw std::runtime_error("failed to create GLFW window");
     }
-
     glfwSetWindowUserPointer(window, this);
+    glfwSetFramebufferSizeCallback(window, [](GLFWwindow* target, int, int) {
+        auto* impl = static_cast<Renderer::Impl*>(glfwGetWindowUserPointer(target));
+        if (impl != nullptr) impl->framebuffer_resized = true;
+    });
     glfwSetKeyCallback(window, [](GLFWwindow* target, int key, int scancode, int action,
                                   int mods) {
         auto* impl = static_cast<Renderer::Impl*>(glfwGetWindowUserPointer(target));
@@ -1051,7 +997,15 @@ void Renderer::Impl::init(int width, int height, const char* title) {
     pipeline_info.pMultisampleState = &multisampling;
     pipeline_info.pDepthStencilState = nullptr;
     pipeline_info.pColorBlendState = &color_blending;
-    pipeline_info.pDynamicState = nullptr;
+    const std::array<VkDynamicState, 2> dynamic_states = {
+        VK_DYNAMIC_STATE_VIEWPORT,
+        VK_DYNAMIC_STATE_SCISSOR,
+    };
+    VkPipelineDynamicStateCreateInfo dynamic_state{};
+    dynamic_state.sType = VK_STRUCTURE_TYPE_PIPELINE_DYNAMIC_STATE_CREATE_INFO;
+    dynamic_state.dynamicStateCount = static_cast<uint32_t>(dynamic_states.size());
+    dynamic_state.pDynamicStates = dynamic_states.data();
+    pipeline_info.pDynamicState = &dynamic_state;
     pipeline_info.layout = pipeline_layout;
     pipeline_info.renderPass = render_pass;
     pipeline_info.subpass = 0;
@@ -1232,7 +1186,139 @@ void Renderer::Impl::upload_mesh(const Mesh& mesh) {
     create_texture(resource, mesh.texture);
 }
 
-void Renderer::Impl::draw(const Actor* const* actors, size_t actor_count) {
+void Renderer::Impl::recreate_swapchain() {
+    int width = 0;
+    int height = 0;
+    glfwGetFramebufferSize(window, &width, &height);
+    if (width == 0 || height == 0) return;
+    check(vkDeviceWaitIdle(device), "vkDeviceWaitIdle");
+
+    VkSurfaceCapabilitiesKHR capabilities{};
+    check(vkGetPhysicalDeviceSurfaceCapabilitiesKHR(physical_device, surface, &capabilities),
+          "vkGetPhysicalDeviceSurfaceCapabilitiesKHR");
+    uint32_t format_count = 0;
+    check(vkGetPhysicalDeviceSurfaceFormatsKHR(physical_device, surface, &format_count, nullptr),
+          "vkGetPhysicalDeviceSurfaceFormatsKHR");
+    std::vector<VkSurfaceFormatKHR> formats(format_count);
+    check(vkGetPhysicalDeviceSurfaceFormatsKHR(physical_device, surface, &format_count, formats.data()),
+          "vkGetPhysicalDeviceSurfaceFormatsKHR");
+    VkSurfaceFormatKHR surface_format = formats.front();
+    for (const VkSurfaceFormatKHR& format : formats) {
+        if (format.format == VK_FORMAT_B8G8R8A8_SRGB &&
+            format.colorSpace == VK_COLOR_SPACE_SRGB_NONLINEAR_KHR) {
+            surface_format = format;
+            break;
+        }
+    }
+    if (surface_format.format != swapchain_format) {
+        throw std::runtime_error("swapchain format changed; renderer recreation is required");
+    }
+    uint32_t present_mode_count = 0;
+    check(vkGetPhysicalDeviceSurfacePresentModesKHR(physical_device, surface, &present_mode_count,
+                                                    nullptr),
+          "vkGetPhysicalDeviceSurfacePresentModesKHR");
+    std::vector<VkPresentModeKHR> present_modes(present_mode_count);
+    check(vkGetPhysicalDeviceSurfacePresentModesKHR(physical_device, surface, &present_mode_count,
+                                                    present_modes.data()),
+          "vkGetPhysicalDeviceSurfacePresentModesKHR");
+    VkPresentModeKHR present_mode = VK_PRESENT_MODE_FIFO_KHR;
+    for (VkPresentModeKHR mode : present_modes) {
+        if (mode == VK_PRESENT_MODE_MAILBOX_KHR) {
+            present_mode = mode;
+            break;
+        }
+    }
+    VkExtent2D extent{};
+    if (capabilities.currentExtent.width != UINT32_MAX) {
+        extent = capabilities.currentExtent;
+    } else {
+        extent.width = std::clamp(static_cast<uint32_t>(width), capabilities.minImageExtent.width,
+                                  capabilities.maxImageExtent.width);
+        extent.height = std::clamp(static_cast<uint32_t>(height), capabilities.minImageExtent.height,
+                                   capabilities.maxImageExtent.height);
+    }
+    uint32_t image_count = capabilities.minImageCount + 1;
+    if (capabilities.maxImageCount > 0 && image_count > capabilities.maxImageCount) {
+        image_count = capabilities.maxImageCount;
+    }
+
+    for (VkFramebuffer framebuffer : framebuffers) {
+        vkDestroyFramebuffer(device, framebuffer, nullptr);
+    }
+    framebuffers.clear();
+    for (VkImageView view : swapchain_image_views) {
+        vkDestroyImageView(device, view, nullptr);
+    }
+    swapchain_image_views.clear();
+    const VkSwapchainKHR old_swapchain = swapchain;
+    if (old_swapchain != VK_NULL_HANDLE) {
+        vkDestroySwapchainKHR(device, old_swapchain, nullptr);
+        swapchain = VK_NULL_HANDLE;
+    }
+
+    VkSwapchainCreateInfoKHR create_info{};
+    create_info.sType = VK_STRUCTURE_TYPE_SWAPCHAIN_CREATE_INFO_KHR;
+    create_info.surface = surface;
+    create_info.minImageCount = image_count;
+    create_info.imageFormat = surface_format.format;
+    create_info.imageColorSpace = surface_format.colorSpace;
+    create_info.imageExtent = extent;
+    create_info.imageArrayLayers = 1;
+    create_info.imageUsage = VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT;
+    std::array<uint32_t, 2> families = {graphics_family, present_family};
+    create_info.imageSharingMode = graphics_family == present_family
+                                       ? VK_SHARING_MODE_EXCLUSIVE
+                                       : VK_SHARING_MODE_CONCURRENT;
+    create_info.queueFamilyIndexCount = graphics_family == present_family ? 0 : 2;
+    create_info.pQueueFamilyIndices = families.data();
+    create_info.preTransform = capabilities.currentTransform;
+    create_info.compositeAlpha = VK_COMPOSITE_ALPHA_OPAQUE_BIT_KHR;
+    create_info.presentMode = present_mode;
+    create_info.clipped = VK_TRUE;
+    create_info.oldSwapchain = VK_NULL_HANDLE;
+    check(vkCreateSwapchainKHR(device, &create_info, nullptr, &swapchain), "vkCreateSwapchainKHR");
+
+    swapchain_extent = extent;
+    uint32_t actual_image_count = 0;
+    check(vkGetSwapchainImagesKHR(device, swapchain, &actual_image_count, nullptr),
+          "vkGetSwapchainImagesKHR");
+    if (actual_image_count > frames.size()) {
+        throw std::runtime_error("resized swapchain needs more frame resources");
+    }
+    swapchain_images.resize(actual_image_count);
+    check(vkGetSwapchainImagesKHR(device, swapchain, &actual_image_count, swapchain_images.data()),
+          "vkGetSwapchainImagesKHR");
+    swapchain_image_views.resize(actual_image_count);
+    for (uint32_t i = 0; i < actual_image_count; ++i) {
+        VkImageViewCreateInfo view_info{};
+        view_info.sType = VK_STRUCTURE_TYPE_IMAGE_VIEW_CREATE_INFO;
+        view_info.image = swapchain_images[i];
+        view_info.viewType = VK_IMAGE_VIEW_TYPE_2D;
+        view_info.format = swapchain_format;
+        view_info.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
+        view_info.subresourceRange.levelCount = 1;
+        view_info.subresourceRange.layerCount = 1;
+        check(vkCreateImageView(device, &view_info, nullptr, &swapchain_image_views[i]),
+              "vkCreateImageView");
+    }
+    framebuffers.resize(actual_image_count);
+    for (uint32_t i = 0; i < actual_image_count; ++i) {
+        VkFramebufferCreateInfo framebuffer_info{};
+        framebuffer_info.sType = VK_STRUCTURE_TYPE_FRAMEBUFFER_CREATE_INFO;
+        framebuffer_info.renderPass = render_pass;
+        framebuffer_info.attachmentCount = 1;
+        framebuffer_info.pAttachments = &swapchain_image_views[i];
+        framebuffer_info.width = swapchain_extent.width;
+        framebuffer_info.height = swapchain_extent.height;
+        framebuffer_info.layers = 1;
+        check(vkCreateFramebuffer(device, &framebuffer_info, nullptr, &framebuffers[i]),
+              "vkCreateFramebuffer");
+    }
+    images_in_flight.assign(actual_image_count, VK_NULL_HANDLE);
+    framebuffer_resized = false;
+}
+
+void Renderer::Impl::draw(const Actor* const* actors, size_t actor_count, const Camera* camera) {
     if (!initialized || actor_count == 0) {
         return;
     }
@@ -1245,6 +1331,7 @@ void Renderer::Impl::draw(const Actor* const* actors, size_t actor_count) {
                                                     frame.image_available,
                                                     VK_NULL_HANDLE, &image_index);
     if (acquire_result == VK_ERROR_OUT_OF_DATE_KHR) {
+        recreate_swapchain();
         return;
     }
     if (acquire_result != VK_SUCCESS && acquire_result != VK_SUBOPTIMAL_KHR) {
@@ -1286,6 +1373,15 @@ void Renderer::Impl::draw(const Actor* const* actors, size_t actor_count) {
 
     vkCmdBeginRenderPass(frame.command_buffer, &render_pass_begin, VK_SUBPASS_CONTENTS_INLINE);
     vkCmdBindPipeline(frame.command_buffer, VK_PIPELINE_BIND_POINT_GRAPHICS, pipeline);
+    VkViewport viewport{};
+    viewport.width = static_cast<float>(swapchain_extent.width);
+    viewport.height = static_cast<float>(swapchain_extent.height);
+    viewport.minDepth = 0.0F;
+    viewport.maxDepth = 1.0F;
+    VkRect2D scissor{};
+    scissor.extent = swapchain_extent;
+    vkCmdSetViewport(frame.command_buffer, 0, 1, &viewport);
+    vkCmdSetScissor(frame.command_buffer, 0, 1, &scissor);
     for (size_t i = 0; i < actor_count; ++i) {
         const Actor& actor = *actors[i];
         if (actor.mesh() == nullptr) continue;
@@ -1301,9 +1397,26 @@ void Renderer::Impl::draw(const Actor* const* actors, size_t actor_count) {
         vkCmdBindDescriptorSets(frame.command_buffer, VK_PIPELINE_BIND_POINT_GRAPHICS, pipeline_layout,
                                 0, 1, &resource.descriptor_set, 0, nullptr);
 
-        const auto position = actor.position();
-        const auto facing = actor.facing();
-        const float scale = 0.35F;
+        auto position = actor.global_position();
+        auto facing = actor.global_facing();
+        float camera_zoom = 1.0F;
+        if (camera != nullptr) {
+            const auto camera_position = camera->global_position();
+            const auto camera_facing = camera->global_facing();
+            const float camera_length = std::sqrt(camera_facing[0] * camera_facing[0] +
+                                                  camera_facing[1] * camera_facing[1]);
+            const float camera_x = camera_length > 0.0001F ? camera_facing[0] / camera_length : 1.0F;
+            const float camera_y = camera_length > 0.0001F ? camera_facing[1] / camera_length : 0.0F;
+            const float dx = position[0] - camera_position[0];
+            const float dy = position[1] - camera_position[1];
+            position = {camera_x * dx + camera_y * dy, -camera_y * dx + camera_x * dy};
+            facing = {camera_x * facing[0] + camera_y * facing[1],
+                      -camera_y * facing[0] + camera_x * facing[1]};
+            camera_zoom = camera->zoom();
+        }
+        const float scale = 0.35F * camera_zoom;
+        const float horizontal_projection =
+            static_cast<float>(swapchain_extent.height) / static_cast<float>(swapchain_extent.width);
         float facing_x = facing[0];
         float facing_y = facing[1];
         const float facing_length = std::sqrt(facing_x * facing_x + facing_y * facing_y);
@@ -1316,10 +1429,10 @@ void Renderer::Impl::draw(const Actor* const* actors, size_t actor_count) {
         }
 
         std::array<float, 20> constants = {{
-            scale * facing_x, scale * facing_y, 0.0F, 0.0F,
-            -scale * facing_y, scale * facing_x, 0.0F, 0.0F,
+            scale * facing_x * horizontal_projection, scale * facing_y, 0.0F, 0.0F,
+            -scale * facing_y * horizontal_projection, scale * facing_x, 0.0F, 0.0F,
             0.0F, 0.0F, 1.0F, 0.0F,
-            position[0], position[1], 0.0F, 1.0F,
+            position[0] * horizontal_projection, position[1], 0.0F, 1.0F,
             0.0F, 0.0F, 0.0F, 0.0F,
         }};
         const std::array<float, 4> color = actor.mesh()->color();
@@ -1354,8 +1467,10 @@ void Renderer::Impl::draw(const Actor* const* actors, size_t actor_count) {
     present_info.pSwapchains = &swapchain;
     present_info.pImageIndices = &image_index;
     VkResult present_result = vkQueuePresentKHR(present_queue, &present_info);
-    if (present_result != VK_SUCCESS && present_result != VK_SUBOPTIMAL_KHR &&
-        present_result != VK_ERROR_OUT_OF_DATE_KHR) {
+    if (present_result == VK_ERROR_OUT_OF_DATE_KHR || present_result == VK_SUBOPTIMAL_KHR ||
+        framebuffer_resized) {
+        recreate_swapchain();
+    } else if (present_result != VK_SUCCESS) {
         check(present_result, "vkQueuePresentKHR");
     }
     (void)present_result;
diff --git a/src/render_loop.cpp b/src/render_loop.cpp
new file mode 100644
index 0000000..f0a3021
--- /dev/null
+++ b/src/render_loop.cpp
@@ -0,0 +1,70 @@
+#include <render.hpp>
+
+namespace boundard::render {
+
+RenderLoop::~RenderLoop() {
+    stop();
+}
+
+void RenderLoop::start(int width, int height, const char* title) {
+    if (running_) return;
+
+    renderer_.init(width, height, title);
+    renderer_.set_input_callback([this](const InputEvent& event) {
+        input_map_.handle_event(event);
+    });
+    running_ = true;
+    thread_ = std::thread(&RenderLoop::run, this);
+}
+
+void RenderLoop::stop() {
+    if (!running_) return;
+    running_ = false;
+    if (thread_.joinable()) thread_.join();
+    renderer_.destroy();
+}
+
+void RenderLoop::set_actors(std::vector<Actor*> actors) {
+    std::lock_guard<std::mutex> lock(actors_mutex_);
+    actors_ = std::move(actors);
+}
+
+void RenderLoop::set_camera(Camera* camera) {
+    std::lock_guard<std::mutex> lock(actors_mutex_);
+    camera_ = camera;
+}
+
+void RenderLoop::poll_events() const {
+    renderer_.poll_events();
+}
+
+bool RenderLoop::should_close() const {
+    return renderer_.should_close();
+}
+
+InputMap& RenderLoop::input() {
+    return input_map_;
+}
+
+const InputMap& RenderLoop::input() const {
+    return input_map_;
+}
+
+void RenderLoop::run() {
+    while (running_) {
+        std::vector<Actor*> actors;
+        Camera* camera = nullptr;
+        {
+            std::lock_guard<std::mutex> lock(actors_mutex_);
+            actors = actors_;
+            camera = camera_;
+        }
+        if (actors.empty()) {
+            std::this_thread::yield();
+            continue;
+        }
+        renderer_.draw(actors.data(), actors.size(), camera);
+    }
+}
+
+}  // namespace boundard::render
diff --git a/src/scene.cpp b/src/scene.cpp
index b16988b..9617b46 100644
--- a/src/scene.cpp
+++ b/src/scene.cpp
@@ -1,10 +1,38 @@
 #include <scene.hpp>
 
 #include <actor.hpp>
+#include <camera.hpp>
 
 #include <utility>
 
 namespace boundard {
+namespace {
+
+void append_actor_tree(Actor* actor, std::vector<Actor*>& output) {
+    if (actor == nullptr) return;
+    output.push_back(actor);
+    for (const std::shared_ptr<Actor>& child : actor->children()) {
+        append_actor_tree(child.get(), output);
+    }
+}
+
+void find_cameras(Actor* actor, const std::string& name, Camera*& first_camera,
+                  Camera*& selected_camera) {
+    if (actor == nullptr || selected_camera != nullptr) return;
+    Camera* camera = dynamic_cast<Camera*>(actor);
+    if (camera != nullptr) {
+        if (first_camera == nullptr) first_camera = camera;
+        if (!name.empty() && camera->name() == name) {
+            selected_camera = camera;
+            return;
+        }
+    }
+    for (const std::shared_ptr<Actor>& child : actor->children()) {
+        find_cameras(child.get(), name, first_camera, selected_camera);
+    }
+}
+
+}  // namespace
 
 Scene::Scene(std::string name) : name_(std::move(name)) {}
 
@@ -36,24 +64,44 @@ void Scene::set_actors(std::vector<std::shared_ptr<Actor>> actors) {
 void Scene::clear() {
     actors_.clear();
     actor_storage_.clear();
+    default_camera_.clear();
+}
+
+void Scene::set_default_camera(std::string name) {
+    default_camera_ = std::move(name);
+}
+
+Camera* Scene::primary_camera() const {
+    Camera* first_camera = nullptr;
+    Camera* selected_camera = nullptr;
+    for (const std::shared_ptr<Actor>& actor : actor_storage_) {
+        find_cameras(actor.get(), default_camera_, first_camera, selected_camera);
+        if (selected_camera != nullptr) return selected_camera;
+    }
+    return first_camera;
 }
 
 const std::vector<Actor*>& Scene::actors() const {
+    actors_.clear();
+    for (const std::shared_ptr<Actor>& actor : actor_storage_) {
+        append_actor_tree(actor.get(), actors_);
+    }
     return actors_;
 }
 
 std::vector<Actor*>& Scene::actors() {
+    static_cast<const Scene&>(*this).actors();
     return actors_;
 }
 
 void Scene::initialize() {
-    for (Actor* actor : actors_) {
+    for (const std::shared_ptr<Actor>& actor : actor_storage_) {
         actor->initialize();
     }
 }
 
 void Scene::process(float dt, const render::InputMap& input) {
-    for (Actor* actor : actors_) {
+    for (const std::shared_ptr<Actor>& actor : actor_storage_) {
         actor->process(dt, input);
     }
 }