feat: move fps and deltatime calculations in core engine

engine/include/engine/app/app.h

@@ -3,6 +3,8 @@
 
 #include "engine/scene/scene.h"
 #include "engine/window/event.hpp"
+#include "engine/time/timestep.h"
+
 #include "engine/export.h"
 
 namespace Core {
@@ -11,7 +13,7 @@ namespace Core {
         virtual ~IApplication() = default;
 
         virtual void OnInit(std::shared_ptr<Scene> scene) {};
-        virtual void OnUpdate() {};
+        virtual void OnUpdate(Timestep dt) {};
         virtual void OnShutdown() {};
         
         virtual void OnEvent(const Event& event) {};

engine/include/engine/renderer/core.h

@@ -30,6 +30,7 @@ private:
     std::shared_ptr<Window> m_window;
     std::unique_ptr<Renderer> m_renderer;
     std::shared_ptr<Scene> m_scene;
+    uint64_t m_elapsed;
     bool m_running;
 };
 

engine/include/engine/time/timestep.h

@@ -0,0 +1,22 @@
+#ifndef TIME_TIMESTEP_H_
+#define TIME_TIMESTEP_H_
+
+namespace Core {
+    class Timestep {
+    public:
+        Timestep(float time = 0.0f)
+            : m_time(time) {}
+
+        [[nodiscard]] float GetSeconds() const { return m_time; }
+        [[nodiscard]] float GetMilliseconds() const { return m_time * 1000.f; }
+
+        operator float() const { return m_time; }
+    public:
+        static Timestep FromMilliseconds(float milliseconds) { return Timestep(milliseconds * 0.001f); }
+        static Timestep FromSeconds(float seconds) { return Timestep(seconds); }
+    private:
+        float m_time;
+    };
+}
+
+#endif // TIME_TIMESTEP_H_

engine/src/renderer/core.cpp

@@ -5,6 +5,8 @@
 #include "engine/window/event.hpp"
 #include "engine/renderer/wavefront.h"
 
+#include "engine/time/timestep.h"
+
 namespace Core {
 
 Engine* Engine::s_instance = nullptr;
@@ -21,10 +23,18 @@ void Engine::Run(std::unique_ptr<IApplication> app) {
 
     m_window->Subscribe(this);
 
+    uint64_t now = SDL_GetPerformanceCounter();
+    m_elapsed = 0;
+
     while (m_running) {
+        m_elapsed = now;
+        now = SDL_GetPerformanceCounter();
+
+        auto dt = Timestep::FromMilliseconds((float)((now - m_elapsed)*1000 / (float)SDL_GetPerformanceFrequency()));
+
         m_window->ProcessEvents();
 
-        m_app->OnUpdate();
+        m_app->OnUpdate(dt);
 
         m_renderer->Render();