Make GL state changes predictable and clean up main.cpp

Engine:
- Create, resize and update functions now restore the bindings they
  touch instead of leaving their own objects bound or resetting to 0
  (Texture, FrameBuffer, Mesh, UniformBuffer)
- Texture::bind/unbind switch back to texture unit 0 afterwards, so
  later texture binds can't replace a material's specular map
- Add gl_get_binding() helper to read the current binding
- Renderer remembers the wireframe mode (new is_wireframe());
  draw_debug_wireframes restores it instead of always disabling it,
  which fixes H having no effect while debug wireframes are shown

main.cpp (same behavior and UI):
- main() only sets up the window and renderer; all GL resources live
  in run() and are released before Renderer::shutdown()
- One function per scene and a shared create_textured_material()
- Split app state into AppState, CameraInput and PerformanceStats;
  drop the duplicate delta_time and static toggle variables
- Move the scene pass to render_scene() and the overlay to
  draw_overlay(); name the light box and overlay constants
- Clear the mouse callback before AppState is destroyed

src/framebuffer.cpp

@@ -16,6 +16,11 @@ Rc<FrameBuffer> FrameBuffer::create(GLsizei width, GLsizei height)
 
     gl_clear_errors();
 
+    // Restored afterwards so creating a framebuffer leaves the caller's bindings intact
+    GLuint previous_fbo = gl_get_binding(GL_FRAMEBUFFER_BINDING);
+    GLuint previous_texture = gl_get_binding(GL_TEXTURE_BINDING_2D);
+    GLuint previous_render_buffer = gl_get_binding(GL_RENDERBUFFER_BINDING);
+
     GLuint id, texture, render_buffer;
 
     glGenFramebuffers(1, &id);
@@ -40,9 +45,9 @@ Rc<FrameBuffer> FrameBuffer::create(GLsizei width, GLsizei height)
 
     GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
     GLenum err = gl_pop_error();
-    glBindFramebuffer(GL_FRAMEBUFFER, 0);
-    glBindTexture(GL_TEXTURE_2D, 0);
-    glBindRenderbuffer(GL_RENDERBUFFER, 0);
+    glBindFramebuffer(GL_FRAMEBUFFER, previous_fbo);
+    glBindTexture(GL_TEXTURE_2D, previous_texture);
+    glBindRenderbuffer(GL_RENDERBUFFER, previous_render_buffer);
 
     if (status != GL_FRAMEBUFFER_COMPLETE || err != GL_NO_ERROR) {
         glDeleteRenderbuffers(1, &render_buffer);
@@ -124,6 +129,11 @@ bool FrameBuffer::resize(GLsizei width, GLsizei height)
 
     gl_clear_errors();
 
+    // Restored afterwards so resizing leaves the caller's bindings intact
+    GLuint previous_fbo = gl_get_binding(GL_FRAMEBUFFER_BINDING);
+    GLuint previous_texture = gl_get_binding(GL_TEXTURE_BINDING_2D);
+    GLuint previous_render_buffer = gl_get_binding(GL_RENDERBUFFER_BINDING);
+
     m_width = width;
     m_height = height;
 
@@ -137,15 +147,12 @@ bool FrameBuffer::resize(GLsizei width, GLsizei height)
     glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH24_STENCIL8,
                           m_width, m_height);
 
-    glBindTexture(GL_TEXTURE_2D, 0);
-    glBindRenderbuffer(GL_RENDERBUFFER, 0);
-
-    // Check completeness without disturbing the caller's framebuffer binding
-    GLint previous_fbo = 0;
-    glGetIntegerv(GL_FRAMEBUFFER_BINDING, &previous_fbo);
     glBindFramebuffer(GL_FRAMEBUFFER, m_id);
     GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
-    glBindFramebuffer(GL_FRAMEBUFFER, static_cast<GLuint>(previous_fbo));
+
+    glBindFramebuffer(GL_FRAMEBUFFER, previous_fbo);
+    glBindTexture(GL_TEXTURE_2D, previous_texture);
+    glBindRenderbuffer(GL_RENDERBUFFER, previous_render_buffer);
 
     GLenum err = gl_pop_error();
     if (status != GL_FRAMEBUFFER_COMPLETE || err != GL_NO_ERROR) {

src/gldebug.cpp

@@ -80,6 +80,13 @@ void set_gl_label(GLenum identifier, GLuint id, const std::string& label)
     glObjectLabel(identifier, id, length, label.c_str());
 }
 
+GLuint gl_get_binding(GLenum binding_query)
+{
+    GLint id = 0;
+    glGetIntegerv(binding_query, &id);
+    return static_cast<GLuint>(id);
+}
+
 void gl_clear_errors()
 {
     gl_pop_error();

src/gldebug.hpp

@@ -13,6 +13,10 @@ void enable_gl_debug_output();
 // Name a GL object so debug messages and tools like RenderDoc show it
 void set_gl_label(GLenum identifier, GLuint id, const std::string& label);
 
+// Object currently bound for a binding query (e.g. GL_TEXTURE_BINDING_2D), used
+// to restore the caller's bindings after creating or updating an object
+GLuint gl_get_binding(GLenum binding_query);
+
 // Discard errors left over from earlier calls
 void gl_clear_errors();
 

src/main.cpp

@@ -3,9 +3,9 @@
 #include <cfloat>
 #include <cstdio>
 #include <random>
+#include <string>
 #include <vector>
 #include <glm/glm.hpp>
-#include <glm/gtc/matrix_transform.hpp>
 #define IMGUI_DEFINE_MATH_OPERATORS
 #include <imgui.h>
 #include <imgui_internal.h>
@@ -14,6 +14,20 @@
 
 using namespace Fan;
 
+/******************** Constants ********************/
+
+// Random lights are scattered inside this box in every scene
+const glm::vec3 LIGHT_BOX_MIN{-10.0f, 1.0f, -3.0f};
+const glm::vec3 LIGHT_BOX_MAX{10.0f, 5.0f, 3.0f};
+
+// Overlay text in the top-left corner of the viewport
+const ImVec4 OVERLAY_COLOR{0.0f, 1.0f, 0.0f, 1.0f};
+constexpr float OVERLAY_X = 20.0f;
+constexpr float OVERLAY_Y = 35.0f;
+constexpr float OVERLAY_LINE_HEIGHT = 17.0f;
+
+/******************** Application state ********************/
+
 // Ring buffer of per-frame measurements, for plotting and stable averages
 struct MetricHistory
 {
@@ -42,47 +56,72 @@ struct MetricHistory
     }
 };
 
-struct UserData
+// Free-fly camera controls, active while the mouse is grabbed
+struct CameraInput
 {
-    Window& window;
-    Camera& camera;
-    float delta_time{};
-    bool mouse_grab{};
-
     float speed{CAMERA_SPEED};
     float sensitivity{CAMERA_SENSITIVITY};
+
+    bool mouse_grab{};
+    bool first_mouse{true}; // Skips the jump from the cursor's position before grabbing
     float last_mouse_x{};
     float last_mouse_y{};
-    bool first_mouse{true};
+};
 
-    bool vsync{true};
-    bool show_debug{};
+// Timings of the scene pass (gpu_timer is null if timer queries are unsupported)
+struct PerformanceStats
+{
+    CpuTimer cpu_timer{};
+    Rc<GpuTimer> gpu_timer{};
 
-    Rc<Texture> logo{};
-
-    // Performance measurements of the scene pass (GPU timer is null if unsupported)
-    CpuTimer scene_cpu_timer{};
-    Rc<GpuTimer> scene_gpu_timer{};
     MetricHistory frame_times{};
     MetricHistory scene_cpu_times{};
     MetricHistory scene_gpu_times{};
+};
+
+struct AppState
+{
+    Window& window;
+    Camera& camera;
+
+    CameraInput input{};
+    PerformanceStats stats{};
+
+    bool vsync{true};
+    bool show_debug{};
+    Rc<Texture> logo{};
 
     std::vector<Rc<Scene>> scenes{};
     size_t selected_scene_index{};
 };
 
-void process_input(Window& window, Camera& camera, UserData& user_data);
+/******************** Declarations ********************/
+
+int run(Window& window);
+
+// Scenes
+std::vector<Rc<Scene>> create_scenes(const Rc<Shader>& shader, const Rc<Mesh>& cube_mesh);
+Rc<Scene> create_sponza_scene(const Rc<Shader>& shader);
+Rc<Scene> create_car_scene(const Rc<Shader>& shader);
+Rc<Scene> create_backpack_scene(const Rc<Shader>& shader, const Rc<Mesh>& cube_mesh);
+Rc<Scene> create_cubes_scene(const Rc<Shader>& shader, const Rc<Mesh>& cube_mesh);
+Rc<Material> create_textured_material(const Rc<Shader>& shader, const std::string& texture_path);
+void add_random_lights(Scene& scene, int point_light_count, int spot_light_count, unsigned int seed);
+
+// Frame
+void process_input(AppState& app);
 void mouse_callback(double pos_x, double pos_y, void* user_data);
+void render_scene(AppState& app, FrameBuffer& framebuffer, const Rc<Shader>& debug_shader);
+
+// UI
 void setup_dockspace();
-void draw_panel_window(UserData& user_data);
-void draw_viewport_window(FrameBuffer& framebuffer, UserData& user_data);
+void draw_panel_window(AppState& app);
+void draw_viewport_window(AppState& app, FrameBuffer& framebuffer);
+void draw_overlay(const AppState& app);
 void plot_metric(const char* label, const MetricHistory& history);
-void add_random_lights(Scene& scene, int point_light_count, int spot_light_count,
-                       const glm::vec3& box_min, const glm::vec3& box_max,
-                       unsigned int seed = std::random_device{}());
 
 template<typename... Args>
-void overlay_text(float offset_x, float offset_y, ImVec4 color, const char* format, Args... args)
+void overlay_text(float offset_x, float offset_y, const char* format, Args... args)
 {
     char buffer[256];
     std::snprintf(buffer, sizeof(buffer), format, args...);
@@ -92,102 +131,132 @@ void overlay_text(float offset_x, float offset_y, ImVec4 color, const char* form
     ImVec2 text_size = ImGui::CalcTextSize(buffer);
 
     draw_list->AddRectFilled(pos - ImVec2{4, 2}, pos + text_size + ImVec2{4, 2}, IM_COL32(0, 0, 0, 160));
-    draw_list->AddText(pos, ImGui::ColorConvertFloat4ToU32(color), buffer);
+    draw_list->AddText(pos, ImGui::ColorConvertFloat4ToU32(OVERLAY_COLOR), buffer);
 }
 
+/******************** Entry point ********************/
+
 int main()
 {
-    /******************** Initialization ********************/
-
     auto window = Window::create(WINDOW_WIDTH, WINDOW_HEIGHT, VERSION_STRING);
     if (!window) return EXIT_FAILURE;
     window->set_vsync(true);
 
     if (!Renderer::init()) return EXIT_FAILURE;
 
+    // Every GL resource created by run() is released when it returns,
+    // before the renderer and the window shut down
+    int exit_code = run(*window);
+
+    Renderer::shutdown();
+    return exit_code;
+}
+
+int run(Window& window)
+{
     Camera camera{{6.0f, 3.0f, 1.0f}};
     camera.fov = 60.0f;
     camera.look_at({0.0f, 1.0f, 0.0f});
 
-    UserData user_data{*window, camera};
-    window->set_callback_user_data(&user_data);
-    window->set_mouse_callback(mouse_callback);
-
-    /******************** Resource loading ********************/
+    AppState app{window, camera};
+    window.set_callback_user_data(&app);
+    window.set_mouse_callback(mouse_callback);
 
+    // Assets never fail to load: missing ones are replaced by fallbacks
     auto shader = ResourceCache::load_shader("./src/shaders/default.vert", "./src/shaders/default.frag");
     auto debug_shader = ResourceCache::load_shader("./src/shaders/debug.vert", "./src/shaders/debug.frag", false);
-
-    Entity sponza = load_obj("./assets/sponza/sponza.obj", shader);
-    Entity car = load_obj("./assets/audi_r8/Audi_R8_2017.obj", shader);
-    Entity backpack = load_obj("./assets/backpack/backpack.obj", shader, true);
-
-    auto cube_texture = ResourceCache::load_texture("./assets/textures/container.jpg");
-    auto default_texture = ResourceCache::load_texture("./assets/textures/wall.jpg");
-    user_data.logo = ResourceCache::load_texture("assets/logo/logo.png");
-
-    user_data.scene_gpu_timer = GpuTimer::create();
-
-    auto cube_mesh = Mesh::create_cube();
-    auto framebuffer = FrameBuffer::create(window->get_width(), window->get_height());
+    app.logo = ResourceCache::load_texture("assets/logo/logo.png");
+    app.stats.gpu_timer = GpuTimer::create();
 
     // Built from memory or sized from the window, failing here means OpenGL is broken
-    if (!cube_mesh || !framebuffer) {
-        Renderer::shutdown();
-        return EXIT_FAILURE;
+    auto cube_mesh = Mesh::create_cube();
+    auto framebuffer = FrameBuffer::create(window.get_width(), window.get_height());
+    if (!cube_mesh || !framebuffer) return EXIT_FAILURE;
+
+    app.scenes = create_scenes(shader, cube_mesh);
+
+    while (!window.should_close()) {
+        window.begin();
+        window.update();
+
+        app.stats.frame_times.push(window.get_delta_time() * 1000.0f);
+        process_input(app);
+
+        Renderer::set_clear_color({0.0f, 0.0f, 0.0f, 1.0f});
+        Renderer::clear();
+
+        // UI layer
+        setup_dockspace();
+        draw_panel_window(app);
+        draw_viewport_window(app, *framebuffer);
+
+        // Scene layer, shown by the viewport window
+        render_scene(app, *framebuffer, debug_shader);
+
+        window.end();
     }
 
-    /******************** Scene construction ********************/
+    // app is about to be destroyed, don't let the window call back into it
+    window.set_mouse_callback(nullptr);
+    return EXIT_SUCCESS;
+}
 
-    // Sponza scene
-    Rc<Scene> sponza_scene = make_rc<Scene>();
-    user_data.scenes.push_back(sponza_scene);
+/******************** Scenes ********************/
 
+std::vector<Rc<Scene>> create_scenes(const Rc<Shader>& shader, const Rc<Mesh>& cube_mesh)
+{
+    return {
+        create_sponza_scene(shader),
+        create_car_scene(shader),
+        create_backpack_scene(shader, cube_mesh),
+        create_cubes_scene(shader, cube_mesh),
+    };
+}
+
+Rc<Scene> create_sponza_scene(const Rc<Shader>& shader)
+{
+    auto scene = make_rc<Scene>();
+
+    Entity sponza = load_obj("./assets/sponza/sponza.obj", shader);
     sponza.transform.position = {0.0f, -0.5f, 0.0f};
     sponza.transform.scale = {0.008f, 0.008f, 0.008f};
-    sponza_scene->add_entity(sponza);
+    scene->add_entity(sponza);
 
-    add_random_lights(*sponza_scene, 4, 4,
-                      glm::vec3(-10.0f, 1.0f, -3.0f), glm::vec3(10.0f, 5.0f, 3.0f),
-                      69420);
+    add_random_lights(*scene, 4, 4, 69420);
+    return scene;
+}
 
-    // Car scene
-    Rc<Scene> car_scene = make_rc<Scene>();
-    user_data.scenes.push_back(car_scene);
+Rc<Scene> create_car_scene(const Rc<Shader>& shader)
+{
+    auto scene = make_rc<Scene>();
 
-    car_scene->add_entity(car);
+    scene->add_entity(load_obj("./assets/audi_r8/Audi_R8_2017.obj", shader));
 
-    add_random_lights(*car_scene, 4, 4,
-                      glm::vec3(-10.0f, 1.0f, -3.0f), glm::vec3(10.0f, 5.0f, 3.0f),
-                      42);
+    add_random_lights(*scene, 4, 4, 42);
+    return scene;
+}
 
-    // Backpack scene
-    Rc<Scene> backpack_scene = make_rc<Scene>();
-    user_data.scenes.push_back(backpack_scene);
+Rc<Scene> create_backpack_scene(const Rc<Shader>& shader, const Rc<Mesh>& cube_mesh)
+{
+    auto scene = make_rc<Scene>();
 
-    backpack_scene->add_entity(backpack);
+    scene->add_entity(load_obj("./assets/backpack/backpack.obj", shader, true));
 
-    auto default_material = make_rc<Material>();
-    default_material->shader = shader;
-    default_material->diffuse_map = default_texture;
-    Entity floor{cube_mesh, default_material};
+    Entity floor{cube_mesh, create_textured_material(shader, "./assets/textures/wall.jpg")};
     floor.transform.position = {0.0f, -3.0f, 0.0f};
     floor.transform.scale = {20.0f, 1.0f, 20.0f};
-    backpack_scene->add_entity(floor);
+    scene->add_entity(floor);
 
-    add_random_lights(*backpack_scene, 4, 4,
-                      glm::vec3(-10.0f, 1.0f, -3.0f), glm::vec3(10.0f, 5.0f, 3.0f),
-                      37);
+    add_random_lights(*scene, 4, 4, 37);
+    return scene;
+}
 
-    // Cubes scene
-    Rc<Scene> cubes_scene = make_rc<Scene>();
-    user_data.scenes.push_back(cubes_scene);
+Rc<Scene> create_cubes_scene(const Rc<Shader>& shader, const Rc<Mesh>& cube_mesh)
+{
+    auto scene = make_rc<Scene>();
+    auto material = create_textured_material(shader, "./assets/textures/container.jpg");
 
-    auto cube_material = make_rc<Material>();
-    cube_material->shader = shader;
-    cube_material->diffuse_map = cube_texture;
-
-    std::vector<glm::vec3> positions{
+    const std::vector<glm::vec3> positions{
         { 0.0f,  0.0f,   0.0f}, { 2.0f,  5.0f, -15.0f}, {-1.5f, -2.2f,  -2.5f},
         {-3.8f, -2.0f, -12.3f}, { 2.4f, -0.4f,  -3.5f}, {-1.7f,  3.0f,  -7.5f},
         { 1.3f, -2.0f,  -2.5f}, { 1.5f,  2.0f,  -2.5f}, { 1.5f,  0.2f,  -1.5f},
@@ -195,92 +264,110 @@ int main()
     };
 
     for (size_t i = 0; i < positions.size(); ++i) {
-        Entity entity{cube_mesh, cube_material};
-        entity.transform.position = positions[i];
-        entity.transform.set_rotation(glm::radians(20.0f * i), {1.0f, 0.3f, 0.5f});
-        cubes_scene->add_entity(entity);
+        Entity cube{cube_mesh, material};
+        cube.transform.position = positions[i];
+        cube.transform.set_rotation(glm::radians(20.0f * i), {1.0f, 0.3f, 0.5f});
+        scene->add_entity(cube);
     }
 
-    add_random_lights(*cubes_scene, 4, 4,
-                      glm::vec3(-10.0f, 1.0f, -3.0f), glm::vec3(10.0f, 5.0f, 3.0f),
-                      152533);
-
-    /******************** Main loop ********************/
-
-    while (!window->should_close()) {
-        window->begin();
-        window->update();
-
-        user_data.delta_time = window->get_delta_time();
-        user_data.frame_times.push(user_data.delta_time * 1000.0f);
-        process_input(*window, camera, user_data);
-
-        Renderer::set_clear_color({0.0f, 0.0f, 0.0f, 1.0f});
-        Renderer::clear();
-
-        // UI Layer
-        setup_dockspace();
-        draw_panel_window(user_data);
-        draw_viewport_window(*framebuffer, user_data);
-
-        // Scene Rendering Layer
-        const Scene& scene = *user_data.scenes[user_data.selected_scene_index];
-
-        int width = framebuffer->get_width();
-        int height = framebuffer->get_height();
-        framebuffer->bind();
-        user_data.scene_cpu_timer.begin();
-        if (user_data.scene_gpu_timer) { user_data.scene_gpu_timer->begin(); }
-
-        Renderer::set_viewport(0, 0, width, height);
-        Renderer::clear();
-        Renderer::draw_scene(scene, camera, width, height);
-        if (user_data.show_debug) {
-            Renderer::draw_debug_wireframes(scene, camera, width, height,
-                                            debug_shader, ResourceCache::get_fallback_mesh());
+    add_random_lights(*scene, 4, 4, 152533);
+    return scene;
 }
 
-        if (user_data.scene_gpu_timer) { user_data.scene_gpu_timer->end(); }
-        user_data.scene_cpu_timer.end();
-        framebuffer->unbind();
-
-        user_data.scene_cpu_times.push(user_data.scene_cpu_timer.get_elapsed_ms());
-        if (user_data.scene_gpu_timer) {
-            user_data.scene_gpu_times.push(user_data.scene_gpu_timer->get_elapsed_ms());
-        }
-
-        window->end();
-    }
-
-    Renderer::shutdown();
-    return EXIT_SUCCESS;
-}
-
-void process_input(Window& window, Camera& camera, UserData& user_data)
+Rc<Material> create_textured_material(const Rc<Shader>& shader, const std::string& texture_path)
 {
+    auto material = make_rc<Material>();
+    material->shader = shader;
+    material->diffuse_map = ResourceCache::load_texture(texture_path);
+    return material;
+}
+
+void add_random_lights(Scene& scene, int point_light_count, int spot_light_count, unsigned int seed)
+{
+    std::mt19937 rng(seed);
+
+    std::uniform_real_distribution<float> random_x(LIGHT_BOX_MIN.x, LIGHT_BOX_MAX.x);
+    std::uniform_real_distribution<float> random_y(LIGHT_BOX_MIN.y, LIGHT_BOX_MAX.y);
+    std::uniform_real_distribution<float> random_z(LIGHT_BOX_MIN.z, LIGHT_BOX_MAX.z);
+    std::uniform_real_distribution<float> random_axis(-1.0f, 1.0f);
+
+    const glm::vec3 light_colors[] = {
+        glm::vec3(1.0f, 1.0f, 1.0f), // White
+        glm::vec3(1.0f, 0.6f, 0.2f), // Warm orange
+        glm::vec3(0.2f, 0.5f, 1.0f), // Cool blue
+        glm::vec3(1.0f, 0.2f, 0.2f), // Red
+        glm::vec3(0.3f, 1.0f, 0.4f), // Green
+        glm::vec3(0.8f, 0.3f, 1.0f)  // Purple
+    };
+    std::uniform_int_distribution<size_t> random_color_index(0, std::size(light_colors) - 1);
+
+    auto random_position = [&]() {
+        return glm::vec3(random_x(rng), random_y(rng), random_z(rng));
+    };
+
+    auto random_direction = [&]() {
+        glm::vec3 direction;
+
+        // Avoid generating a vector that is too close to zero
+        do {
+            direction = glm::vec3(random_axis(rng), random_axis(rng), random_axis(rng));
+        } while (glm::dot(direction, direction) < 0.001f);
+
+        return glm::normalize(direction);
+    };
+
+    auto random_color = [&]() { return light_colors[random_color_index(rng)]; };
+
+    for (int i = 0; i < point_light_count; ++i) {
+        PointLight light;
+        light.position = random_position();
+
+        glm::vec3 color = random_color();
+        light.diffuse = color;
+        light.specular = glm::mix(color, glm::vec3(1.0f), 0.25f);
+
+        scene.light_environment.point_lights.push_back(light);
+    }
+
+    for (int i = 0; i < spot_light_count; ++i) {
+        SpotLight light;
+        light.position = random_position();
+        light.direction = random_direction();
+
+        glm::vec3 color = random_color();
+        light.diffuse = color;
+        light.specular = glm::mix(color, glm::vec3(1.0f), 0.25f);
+
+        // Slightly wider soft outer cone than the default
+        light.outer_cut_off = glm::cos(glm::radians(17.5f));
+
+        scene.light_environment.spot_lights.push_back(light);
+    }
+}
+
+/******************** Frame ********************/
+
+void process_input(AppState& app)
+{
+    Window& window = app.window;
+    CameraInput& input = app.input;
+
     if (window.is_key_pressed(GLFW_KEY_ESCAPE)) window.set_should_close(true);
-
-    static bool wireframe = false;
-    if (window.is_key_pressed(GLFW_KEY_H)) {
-        wireframe = !wireframe;
-        Renderer::set_wireframe(wireframe);
-    }
-
-    static bool fullscreen = false;
-    if (window.is_key_pressed(GLFW_KEY_F11)) {
-        fullscreen = !fullscreen;
-        window.set_fullscreen(fullscreen);
-    }
+    if (window.is_key_pressed(GLFW_KEY_H)) Renderer::set_wireframe(!Renderer::is_wireframe());
+    if (window.is_key_pressed(GLFW_KEY_F11)) window.set_fullscreen(!window.is_fullscreen());
 
     if (window.is_key_pressed(GLFW_KEY_INSERT)) {
-        user_data.mouse_grab = !user_data.mouse_grab;
-        user_data.first_mouse = true;
-        window.set_mouse_grab(user_data.mouse_grab);
+        input.mouse_grab = !input.mouse_grab;
+        input.first_mouse = true;
+        window.set_mouse_grab(input.mouse_grab);
     }
 
-    if (!user_data.mouse_grab) return;
+    if (!input.mouse_grab) return;
+
+    Camera& camera = app.camera;
+    float boost = window.is_key_down(GLFW_KEY_LEFT_SHIFT) ? 2.0f : 1.0f;
+    float velocity = input.speed * window.get_delta_time() * boost;
 
-    float velocity = user_data.speed * user_data.delta_time * (window.is_key_down(GLFW_KEY_LEFT_SHIFT) ? 2.0f : 1.0f);
     if (window.is_key_down(GLFW_KEY_W)) camera.position += camera.get_front() * velocity;
     if (window.is_key_down(GLFW_KEY_S)) camera.position -= camera.get_front() * velocity;
     if (window.is_key_down(GLFW_KEY_A)) camera.position -= camera.get_right() * velocity;
@@ -289,28 +376,60 @@ void process_input(Window& window, Camera& camera, UserData& user_data)
 
 void mouse_callback(double pos_x, double pos_y, void* user_data)
 {
-    auto* data = static_cast<UserData*>(user_data);
-    if (!data->mouse_grab) return;
+    AppState& app = *static_cast<AppState*>(user_data);
+    CameraInput& input = app.input;
+    if (!input.mouse_grab) return;
 
-    if (data->first_mouse) {
-        data->last_mouse_x = pos_x;
-        data->last_mouse_y = pos_y;
-        data->first_mouse = false;
+    if (input.first_mouse) {
+        input.last_mouse_x = pos_x;
+        input.last_mouse_y = pos_y;
+        input.first_mouse = false;
     }
 
-    float delta_x = (pos_x - data->last_mouse_x) * data->sensitivity;
-    float delta_y = (data->last_mouse_y - pos_y) * data->sensitivity;
+    float delta_x = (pos_x - input.last_mouse_x) * input.sensitivity;
+    float delta_y = (input.last_mouse_y - pos_y) * input.sensitivity;
 
-    data->last_mouse_x = pos_x;
-    data->last_mouse_y = pos_y;
-    data->camera.rotate(delta_x, delta_y);
+    input.last_mouse_x = pos_x;
+    input.last_mouse_y = pos_y;
+    app.camera.rotate(delta_x, delta_y);
 }
 
+void render_scene(AppState& app, FrameBuffer& framebuffer, const Rc<Shader>& debug_shader)
+{
+    const Scene& scene = *app.scenes[app.selected_scene_index];
+    PerformanceStats& stats = app.stats;
+
+    int width = framebuffer.get_width();
+    int height = framebuffer.get_height();
+
+    framebuffer.bind();
+    stats.cpu_timer.begin();
+    if (stats.gpu_timer) { stats.gpu_timer->begin(); }
+
+    Renderer::set_viewport(0, 0, width, height);
+    Renderer::clear();
+    Renderer::draw_scene(scene, app.camera, width, height);
+    if (app.show_debug) {
+        Renderer::draw_debug_wireframes(scene, app.camera, width, height,
+                                        debug_shader, ResourceCache::get_fallback_mesh());
+    }
+
+    if (stats.gpu_timer) { stats.gpu_timer->end(); }
+    stats.cpu_timer.end();
+    framebuffer.unbind();
+
+    stats.scene_cpu_times.push(stats.cpu_timer.get_elapsed_ms());
+    if (stats.gpu_timer) { stats.scene_gpu_times.push(stats.gpu_timer->get_elapsed_ms()); }
+}
+
+/******************** UI ********************/
+
 void setup_dockspace()
 {
     ImGuiID dockspace_id = ImGui::GetID("Dockspace");
     ImGuiViewport* viewport = ImGui::GetMainViewport();
 
+    // Build the default layout once: panel on the left, viewport on the right
     static bool first_time = true;
     if (first_time) {
         first_time = false;
@@ -329,44 +448,45 @@ void setup_dockspace()
     ImGui::DockSpaceOverViewport(dockspace_id, viewport, ImGuiDockNodeFlags_None);
 }
 
-void draw_panel_window(UserData& user_data)
+void draw_panel_window(AppState& app)
 {
     ImGui::Begin("Panel");
 
-    if (user_data.logo) ImGui::Image(user_data.logo->get_id(), {50.0f, 50.0f}, {0.0f, 1.0f}, {1.0f, 0.0f});
+    // Header: logo with the title vertically centered next to it
+    if (app.logo) ImGui::Image(app.logo->get_id(), {50.0f, 50.0f}, {0.0f, 1.0f}, {1.0f, 0.0f});
     ImGui::SameLine();
     ImGui::SetCursorPosY(ImGui::GetCursorPosY() + (50.0f - ImGui::GetTextLineHeight()) * 0.5f);
     ImGui::Text("Fan Engine");
 
     ImGui::SeparatorText("General Settings");
 
-    if (ImGui::Checkbox("VSync", &user_data.vsync)) {
-        user_data.window.set_vsync(user_data.vsync);
+    if (ImGui::Checkbox("VSync", &app.vsync)) {
+        app.window.set_vsync(app.vsync);
     }
-    ImGui::Checkbox("Debug Wireframes", &user_data.show_debug);
+    ImGui::Checkbox("Debug Wireframes", &app.show_debug);
 
     ImGui::SeparatorText("Scene Selector");
 
-    for (size_t i = 0; i < user_data.scenes.size(); ++i) {
+    for (size_t i = 0; i < app.scenes.size(); ++i) {
         char label[64];
         ImFormatString(label, IM_ARRAYSIZE(label), "Scene %zu", i);
-        if (ImGui::RadioButton(label, user_data.selected_scene_index == i)) {
-            user_data.selected_scene_index = i;
+        if (ImGui::RadioButton(label, app.selected_scene_index == i)) {
+            app.selected_scene_index = i;
         }
     }
 
     ImGui::SeparatorText("Camera Settings");
 
-    ImGui::DragFloat3("Position", &user_data.camera.position.x, 0.1f, -20.0f, 20.0f, "%.1f");
-    ImGui::SliderFloat("FOV", &user_data.camera.fov, 30.0f, 100.0f, "%.1f");
+    ImGui::DragFloat3("Position", &app.camera.position.x, 0.1f, -20.0f, 20.0f, "%.1f");
+    ImGui::SliderFloat("FOV", &app.camera.fov, 30.0f, 100.0f, "%.1f");
 
     ImGui::SeparatorText("Performance");
 
     ImGui::TextDisabled("Disable VSync for accurate frame times");
-    plot_metric("Frame", user_data.frame_times);
-    plot_metric("Scene CPU", user_data.scene_cpu_times);
-    if (user_data.scene_gpu_timer) {
-        plot_metric("Scene GPU", user_data.scene_gpu_times);
+    plot_metric("Frame", app.stats.frame_times);
+    plot_metric("Scene CPU", app.stats.scene_cpu_times);
+    if (app.stats.gpu_timer) {
+        plot_metric("Scene GPU", app.stats.scene_gpu_times);
     } else {
         ImGui::TextDisabled("Scene GPU: timer queries not supported");
     }
@@ -382,7 +502,7 @@ void draw_panel_window(UserData& user_data)
     ImGui::End();
 }
 
-void draw_viewport_window(FrameBuffer& framebuffer, UserData& user_data)
+void draw_viewport_window(AppState& app, FrameBuffer& framebuffer)
 {
     ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2{0.0f, 0.0f});
     ImGui::Begin("Viewport");
@@ -391,32 +511,48 @@ void draw_viewport_window(FrameBuffer& framebuffer, UserData& user_data)
     if (size.x > 0 && size.y > 0) {
         // Size the framebuffer in physical pixels so HiDPI displays render at full resolution
         ImVec2 scale = ImGui::GetIO().DisplayFramebufferScale;
-        GLsizei fb_width = static_cast<GLsizei>(size.x * scale.x);
-        GLsizei fb_height = static_cast<GLsizei>(size.y * scale.y);
-        if (fb_width != framebuffer.get_width() || fb_height != framebuffer.get_height()) {
-            framebuffer.resize(fb_width, fb_height);
+        GLsizei width = static_cast<GLsizei>(size.x * scale.x);
+        GLsizei height = static_cast<GLsizei>(size.y * scale.y);
+        if (width != framebuffer.get_width() || height != framebuffer.get_height()) {
+            framebuffer.resize(width, height);
         }
+
+        // Flip vertically: OpenGL textures start at the bottom row
         ImGui::Image(framebuffer.get_texture_id(), size, ImVec2{0.0f, 1.0f}, ImVec2{1.0f, 0.0f});
     }
 
-    // Overlays (averaged over the last MetricHistory::SIZE frames so they're readable)
-    float frame_ms = user_data.frame_times.average();
-    float fps = frame_ms > 0.0f ? 1000.0f / frame_ms : 0.0f;
-    overlay_text(20.0f, 35.0f, {0.0f, 1.0f, 0.0f, 1.0f}, "%s", VERSION_STRING);
-    overlay_text(20.0f, 52.0f, {0.0f, 1.0f, 0.0f, 1.0f}, "FPS: %.1f", fps);
-    overlay_text(20.0f, 69.0f, {0.0f, 1.0f, 0.0f, 1.0f}, "Frame time: %.2f ms", frame_ms);
-    overlay_text(20.0f, 86.0f, {0.0f, 1.0f, 0.0f, 1.0f}, "Scene CPU: %.2f ms", user_data.scene_cpu_times.average());
-    if (user_data.scene_gpu_timer) {
-        overlay_text(20.0f, 103.0f, {0.0f, 1.0f, 0.0f, 1.0f}, "Scene GPU: %.2f ms", user_data.scene_gpu_times.average());
-    } else {
-        overlay_text(20.0f, 103.0f, {0.0f, 1.0f, 0.0f, 1.0f}, "%s", "Scene GPU: n/a");
-    }
-    if (user_data.mouse_grab) { overlay_text(20.0f, 120.0f, {0.0f, 1.0f, 0.0f, 1.0f}, "%s", "INPUT LOCKED"); }
+    draw_overlay(app);
 
     ImGui::End();
     ImGui::PopStyleVar();
 }
 
+void draw_overlay(const AppState& app)
+{
+    const PerformanceStats& stats = app.stats;
+
+    // Averaged over the last MetricHistory::SIZE frames so the numbers are readable
+    float frame_ms = stats.frame_times.average();
+    float fps = frame_ms > 0.0f ? 1000.0f / frame_ms : 0.0f;
+
+    float y = OVERLAY_Y;
+    auto line = [&y](const char* format, auto... args) {
+        overlay_text(OVERLAY_X, y, format, args...);
+        y += OVERLAY_LINE_HEIGHT;
+    };
+
+    line("%s", VERSION_STRING);
+    line("FPS: %.1f", fps);
+    line("Frame time: %.2f ms", frame_ms);
+    line("Scene CPU: %.2f ms", stats.scene_cpu_times.average());
+    if (stats.gpu_timer) {
+        line("Scene GPU: %.2f ms", stats.scene_gpu_times.average());
+    } else {
+        line("%s", "Scene GPU: n/a");
+    }
+    if (app.input.mouse_grab) { line("%s", "INPUT LOCKED"); }
+}
+
 void plot_metric(const char* label, const MetricHistory& history)
 {
     char overlay[32];
@@ -426,74 +562,3 @@ void plot_metric(const char* label, const MetricHistory& history)
     ImGui::PlotLines(label, history.values.data(), static_cast<int>(history.values.size()),
                      static_cast<int>(history.offset), overlay, 0.0f, FLT_MAX, ImVec2{0.0f, 40.0f});
 }
-
-void add_random_lights(Scene& scene, int point_light_count, int spot_light_count,
-                       const glm::vec3& box_min, const glm::vec3& box_max,
-                       unsigned int seed/* = std::random_device{}()*/)
-{
-    std::mt19937 rng(seed);
-
-    std::uniform_real_distribution<float> random_x(box_min.x, box_max.x);
-    std::uniform_real_distribution<float> random_y(box_min.y, box_max.y);
-    std::uniform_real_distribution<float> random_z(box_min.z, box_max.z);
-
-    std::uniform_real_distribution<float> random_direction(-1.0f, 1.0f);
-    std::uniform_real_distribution<float> random_intensity(0.5f, 1.5f);
-
-    const glm::vec3 light_colors[] = {
-        glm::vec3(1.0f, 1.0f, 1.0f), // White
-        glm::vec3(1.0f, 0.6f, 0.2f), // Warm orange
-        glm::vec3(0.2f, 0.5f, 1.0f), // Cool blue
-        glm::vec3(1.0f, 0.2f, 0.2f), // Red
-        glm::vec3(0.3f, 1.0f, 0.4f), // Green
-        glm::vec3(0.8f, 0.3f, 1.0f)  // Purple
-    };
-
-    std::uniform_int_distribution<size_t> randomColor(0, std::size(light_colors) - 1);
-
-    auto generateDirection = [&]() {
-        glm::vec3 direction;
-
-        // Avoid generating a vector that is too close to zero.
-        do {
-            direction = glm::vec3(random_direction(rng), random_direction(rng), random_direction(rng));
-        } while (glm::dot(direction, direction) < 0.001f);
-
-        return glm::normalize(direction);
-    };
-
-    auto generateColor = [&]() { return light_colors[randomColor(rng)]; };
-
-    // Generate point lights
-    for (int i = 0; i < point_light_count; ++i) {
-        PointLight light;
-
-        light.position = glm::vec3(random_x(rng), random_y(rng), random_z(rng));
-        glm::vec3 color = generateColor();
-        light.diffuse = color;
-        light.specular = glm::mix(color, glm::vec3(1.0f), 0.25f);
-
-        scene.light_environment.point_lights.push_back(light);
-    }
-
-    // Generate spot lights
-    for (int i = 0; i < spot_light_count; ++i) {
-        SpotLight light;
-
-        light.position = glm::vec3(random_x(rng), random_y(rng), random_z(rng));
-        light.direction = generateDirection();
-        glm::vec3 color = generateColor();
-        light.ambient = glm::vec3(0.0f);
-        light.diffuse = color;
-        light.specular = glm::mix(color, glm::vec3(1.0f), 0.25f);
-
-        // Narrow inner cone and slightly wider soft outer cone
-        light.cut_off = glm::cos(glm::radians(12.5f));
-        light.outer_cut_off = glm::cos(glm::radians(17.5f));
-        light.constant = 1.0f;
-        light.linear = 0.09f;
-        light.quadratic = 0.032f;
-
-        scene.light_environment.spot_lights.push_back(light);
-    }
-}

src/mesh.cpp

@@ -39,6 +39,11 @@ Rc<Mesh> Mesh::create(const std::vector<Vertex>& vertices,
 
     gl_clear_errors();
 
+    // Restored afterwards so creating a mesh leaves the caller's bindings intact
+    // (the index buffer binding is part of the VAO, restoring the VAO covers it)
+    GLuint previous_vao = gl_get_binding(GL_VERTEX_ARRAY_BINDING);
+    GLuint previous_vbo = gl_get_binding(GL_ARRAY_BUFFER_BINDING);
+
     GLuint VBO{}, VAO{}, EBO{};
     glGenBuffers(1, &VBO);
     glGenVertexArrays(1, &VAO);
@@ -66,8 +71,9 @@ Rc<Mesh> Mesh::create(const std::vector<Vertex>& vertices,
     glEnableVertexAttribArray(1);
     glEnableVertexAttribArray(2);
 
-    // Unbind so later GL_ELEMENT_ARRAY_BUFFER binds can't modify this VAO
-    glBindVertexArray(0);
+    // Also stops later GL_ELEMENT_ARRAY_BUFFER binds from modifying this VAO
+    glBindVertexArray(previous_vao);
+    glBindBuffer(GL_ARRAY_BUFFER, previous_vbo);
 
     // Buffer uploads can fail with GL_OUT_OF_MEMORY on large meshes
     GLenum err = gl_pop_error();

src/renderer.cpp

@@ -11,6 +11,7 @@ namespace Fan
 
 Rc<UniformBuffer> Renderer::s_camera_ubo = nullptr;
 Rc<UniformBuffer> Renderer::s_light_ubo = nullptr;
+bool Renderer::s_wireframe = false;
 
 bool Renderer::init()
 {
@@ -52,9 +53,15 @@ void Renderer::set_clear_color(const glm::vec4& color)
 
 void Renderer::set_wireframe(bool enabled)
 {
+    s_wireframe = enabled;
     glPolygonMode(GL_FRONT_AND_BACK, enabled ? GL_LINE : GL_FILL);
 }
 
+bool Renderer::is_wireframe()
+{
+    return s_wireframe;
+}
+
 void Renderer::clear()
 {
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
@@ -129,6 +136,7 @@ void Renderer::draw_debug_wireframes(const Scene& scene, const Camera& camera,
     debug_shader->bind();
     debug_shader->set_mat4("u_view_projection", camera.get_view_projection_matrix(screen_width, screen_height));
 
+    bool previous_wireframe = s_wireframe;
     set_wireframe(true);
 
     // Draw all standard entities (green)
@@ -161,8 +169,7 @@ void Renderer::draw_debug_wireframes(const Scene& scene, const Camera& camera,
         default_mesh->draw();
     }
 
-    // Restore state
-    set_wireframe(false);
+    set_wireframe(previous_wireframe);
 }
 
 void Renderer::update_global_data(const Scene& scene, const Camera& camera,

src/renderer.hpp

@@ -19,6 +19,7 @@ public:
     static void set_viewport(int x, int y, int width, int height);
     static void set_clear_color(const glm::vec4& color);
     static void set_wireframe(bool enabled); // Global, stays on until disabled
+    static bool is_wireframe();
 
     static void clear();
 
@@ -28,7 +29,8 @@ public:
                            int screen_width, int screen_height);
 
     // debug_shader needs u_model, u_view_projection and u_color. default_mesh is
-    // drawn for entities without a mesh and for lights. Disables wireframe when done
+    // drawn for entities without a mesh and for lights. Restores the previous
+    // wireframe mode when done
     static void draw_debug_wireframes(const Scene& scene, const Camera& camera,
                                       int screen_width, int screen_height,
                                       const Rc<Shader>& debug_shader,
@@ -37,6 +39,7 @@ public:
 private:
     static Rc<UniformBuffer> s_camera_ubo;
     static Rc<UniformBuffer> s_light_ubo;
+    static bool s_wireframe;
 
     static void update_global_data(const Scene& scene, const Camera& camera,
                                    int screen_width, int screen_height);

src/texture.cpp

@@ -38,6 +38,8 @@ Rc<Texture> Texture::create_from_pixels(GLsizei width, GLsizei height,
 
     gl_clear_errors();
 
+    GLuint previous_texture = gl_get_binding(GL_TEXTURE_BINDING_2D);
+
     GLuint texture;
     glGenTextures(1, &texture);
     glBindTexture(GL_TEXTURE_2D, texture);
@@ -56,6 +58,7 @@ Rc<Texture> Texture::create_from_pixels(GLsizei width, GLsizei height,
 
     // Upload can fail with GL_OUT_OF_MEMORY on large images
     GLenum err = gl_pop_error();
+    glBindTexture(GL_TEXTURE_2D, previous_texture);
     if (err != GL_NO_ERROR) {
         Log::error() << "Could not upload texture " << name << ": " << gl_error_string(err);
         glDeleteTextures(1, &texture);
@@ -97,12 +100,16 @@ void Texture::bind(GLuint slot/* = 0*/) const
 {
     glActiveTexture(GL_TEXTURE0 + slot);
     glBindTexture(GL_TEXTURE_2D, m_id);
+
+    // Keep unit 0 active so later texture binds can't land on this slot
+    glActiveTexture(GL_TEXTURE0);
 }
 
 void Texture::unbind(GLuint slot/* = 0*/)
 {
     glActiveTexture(GL_TEXTURE0 + slot);
     glBindTexture(GL_TEXTURE_2D, 0);
+    glActiveTexture(GL_TEXTURE0);
 }
 
 } // namespace Fan

src/texture.hpp

@@ -29,7 +29,7 @@ public:
 
     GLuint get_id() const;
 
-    // slot is the texture unit, which is left as the active unit
+    // slot is the texture unit. The active unit is reset to 0 afterwards
     void bind(GLuint slot = 0) const;
     static void unbind(GLuint slot = 0);
 

src/uniformbuffer.cpp

@@ -26,6 +26,9 @@ Rc<UniformBuffer> UniformBuffer::create(size_t size, GLuint binding_point)
 
     gl_clear_errors();
 
+    // glBindBufferBase also changes the generic binding, restore it afterwards
+    GLuint previous_buffer = gl_get_binding(GL_UNIFORM_BUFFER_BINDING);
+
     GLuint id;
 
     glGenBuffers(1, &id);
@@ -33,7 +36,7 @@ Rc<UniformBuffer> UniformBuffer::create(size_t size, GLuint binding_point)
 
     glBufferData(GL_UNIFORM_BUFFER, size, nullptr, GL_DYNAMIC_DRAW);
     glBindBufferBase(GL_UNIFORM_BUFFER, binding_point, id);
-    glBindBuffer(GL_UNIFORM_BUFFER, 0);
+    glBindBuffer(GL_UNIFORM_BUFFER, previous_buffer);
 
     GLenum err = gl_pop_error();
     if (err != GL_NO_ERROR) {
@@ -80,9 +83,11 @@ void UniformBuffer::update(const void* data, size_t size, size_t offset) const
         return;
     }
 
+    GLuint previous_buffer = gl_get_binding(GL_UNIFORM_BUFFER_BINDING);
+
     glBindBuffer(GL_UNIFORM_BUFFER, m_id);
     glBufferSubData(GL_UNIFORM_BUFFER, offset, size, data);
-    glBindBuffer(GL_UNIFORM_BUFFER, 0);
+    glBindBuffer(GL_UNIFORM_BUFFER, previous_buffer);
 }
 
 } // namespace Fan