From 78ef93bcf513276e0eec2304db6ebbca284d76e7 Mon Sep 17 00:00:00 2001
From: SeanOMik <seanomik@gmail.com>
Date: Fri, 14 Oct 2022 23:17:22 -0400
Subject: [PATCH] Start working on fixed timestep

Frame interprelation still needs to be done to make a slow TPS look smooth
---
 .clang-tidy                                   |  4 ++
 examples/dev_testing/src/main.cpp             |  6 +-
 include/simpleengine/camera.h                 | 11 ++++
 .../ecs/component/transform_component.h       |  9 ++-
 include/simpleengine/game.h                   | 13 +++--
 include/simpleengine/gfx/light.h              |  2 +-
 include/simpleengine/gfx/renderer.h           | 13 +++--
 include/simpleengine/renderable.h             |  2 +-
 include/simpleengine/scene.h                  |  8 ++-
 resources/shaders/core/3d/fragment_core.glsl  |  2 +-
 src/game.cpp                                  | 36 ++++++++----
 src/gfx/renderer.cpp                          | 55 ++++++++++++++-----
 src/scene.cpp                                 | 21 ++++---
 13 files changed, 133 insertions(+), 49 deletions(-)

diff --git a/.clang-tidy b/.clang-tidy
index b3fa1d3..adcf3e8 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -35,5 +35,9 @@ CheckOptions:
     value: "NULL"
   - key: readability-magic-numbers
     value: "0"
+  - key: cppcoreguidelines-avoid-magic-numbers
+    value: "0"
+  - key: cppcoreguidelines-non-private-member-variables-in-classes
+    value: "0"
 ---
 
diff --git a/examples/dev_testing/src/main.cpp b/examples/dev_testing/src/main.cpp
index ca77c59..e87abfe 100644
--- a/examples/dev_testing/src/main.cpp
+++ b/examples/dev_testing/src/main.cpp
@@ -70,11 +70,12 @@ int main(int argc, char *argv[]) {
     // Create a renderer
     auto renderer = std::make_shared<se::gfx::Renderer>(game.get_window(), core_shader, camera);
     renderer->initialize();
-    game.add_renderable(renderer);
+    //game.add_renderable(renderer);
 
     // Create a Scene and give it the renderer
     auto scene = std::make_shared<se::Scene>(renderer);
-    game.add_event(scene);
+    //game.add_event(scene);
+    game.add_renderable(scene); 
 
     se::ecs::Entity other_e = scene->create_entity();
     other_e.add_component<se::ModelComponent>("examples/dev_testing/resources/transparent_window.fbx",
@@ -95,6 +96,7 @@ int main(int argc, char *argv[]) {
 
     se::ecs::Entity brick_e = scene->create_entity();
     brick_e.add_component<se::ModelComponent>("examples/dev_testing/resources/bricks/bricks.fbx");
+    brick_e.add_component<se::RotatingComponent>();
     auto &brick_transf = brick_e.add_component<se::TransformComponent>();
     brick_transf.translate(6.f, -0.5f, 1.f);
 
diff --git a/include/simpleengine/camera.h b/include/simpleengine/camera.h
index 3a5f012..bf7c3a5 100644
--- a/include/simpleengine/camera.h
+++ b/include/simpleengine/camera.h
@@ -10,10 +10,21 @@
 #include <glm/glm.hpp>
 
 namespace simpleengine {
+    namespace gfx {
+        class Renderer;
+    }
+
     class Camera : public simpleengine::Event {
+    friend gfx::Renderer;
     private:
         GLFWwindow* window;
+
+        glm::vec3 last_position;
+        glm::vec3 last_rotation;
+        glm::mat4 last_view_matrix;
+        glm::vec3 last_camera_front;
     public:
+
         glm::vec3 position;
         glm::vec3 rotation;
         gfx::Shader shader;
diff --git a/include/simpleengine/ecs/component/transform_component.h b/include/simpleengine/ecs/component/transform_component.h
index f0fa948..9a15519 100644
--- a/include/simpleengine/ecs/component/transform_component.h
+++ b/include/simpleengine/ecs/component/transform_component.h
@@ -1,5 +1,6 @@
 #pragma once
 
+//#include "simpleengine/scene.h"
 #include <glm/ext/matrix_transform.hpp>
 #include <glm/glm.hpp>
 
@@ -9,14 +10,18 @@ namespace simpleengine {
      * 
      */
     class TransformComponent {
+    friend class Scene;
+    private:
+        // This is the transform from the last render loop. The renderer uses this for frame interprelation
+        glm::mat4 last_transform_matrix;
     public:
         glm::mat4 transform_matrix;
 
-        TransformComponent() : transform_matrix(glm::mat4(1.f)) {
+        TransformComponent() : transform_matrix(1.f), last_transform_matrix(1.f) {
             
         }
 
-        TransformComponent(glm::mat4 transform_matrix) : transform_matrix(transform_matrix) {
+        TransformComponent(glm::mat4 transform_matrix) : transform_matrix(transform_matrix), last_transform_matrix(1.f) {
 
         }
 
diff --git a/include/simpleengine/game.h b/include/simpleengine/game.h
index 2f1ad17..ce6bd95 100644
--- a/include/simpleengine/game.h
+++ b/include/simpleengine/game.h
@@ -42,8 +42,8 @@ namespace simpleengine {
 
         void update(const float& delta_time);
         void handle_input(const float& delta_time);
-        void render_window(const float& delta_time);
-        void render_items(const float& delta_time);
+        void render_window(const float& interpolate_alpha, const float& delta_time);
+        void render_items(const float& interpolate_alpha, const float& delta_time);
         void exit();
         int run();
 
@@ -63,8 +63,13 @@ namespace simpleengine {
         // FPS related stuff
         void update_enabled_vsync() const;
         void limit_framerate(const float& delta_time) const; // Triggered at the end of a draw to help limit the FPS to `fps_limit`.
-        int fps_limit;
-        bool enable_vsync;
+        int fps_limit = -1;
+        bool enable_vsync = true;
+
+        int max_engine_tps = 60; // The maximum engine TPS
+        double tps_accumulator = 0.f;
+        //int engine_ticks_second = 0; // The amount of ticks in a second
+        //double last_sec_engine_tick; // The time of the last second
 
         float get_delta_time();
 
diff --git a/include/simpleengine/gfx/light.h b/include/simpleengine/gfx/light.h
index f534792..a522f1c 100644
--- a/include/simpleengine/gfx/light.h
+++ b/include/simpleengine/gfx/light.h
@@ -23,7 +23,7 @@ namespace simpleengine::gfx {
             shader.unuse();
         }
 
-        virtual void render() override {
+        virtual void render(const float& interpolate_alpha, const float& frame_time) override {
 
         }
     };
diff --git a/include/simpleengine/gfx/renderer.h b/include/simpleengine/gfx/renderer.h
index bb0e06b..8536602 100644
--- a/include/simpleengine/gfx/renderer.h
+++ b/include/simpleengine/gfx/renderer.h
@@ -17,9 +17,10 @@ namespace simpleengine::gfx {
     public:
         RenderingType rendering_type;
         gfx::Mesh* rendering_mesh;
+        glm::mat4 last_transform_mat;
         glm::mat4 transform_mat;
 
-        RenderingJob(RenderingType rendering_type, gfx::Mesh& mesh, glm::mat4 position);
+        RenderingJob(RenderingType rendering_type, gfx::Mesh& mesh, glm::mat4 last_pos, glm::mat4 position);
     };
 
     class Renderer : public simpleengine::Renderable {
@@ -43,7 +44,7 @@ namespace simpleengine::gfx {
         void enable_debug();
 
         virtual void sort_jobs();
-        virtual void queue_job(RenderingType rendering_type, gfx::Mesh& mesh, glm::mat4 position);
+        virtual void queue_job(RenderingType rendering_type, gfx::Mesh& mesh, glm::mat4 last_position, glm::mat4 position);
         virtual void queue_job(RenderingJob job);
         virtual void create_job_buffers(RenderingJob& job);
 
@@ -52,7 +53,7 @@ namespace simpleengine::gfx {
 
         virtual void update(const float& delta_time) override;
         
-        virtual void render() override;
+        virtual void render(const float& interpolate_alpha, const float& frame_time) override;
 
         /**
          * @brief Renders a single job.
@@ -61,8 +62,8 @@ namespace simpleengine::gfx {
          * @return true if the job was rendered successfully.
          * @return false if there was an error when trying to render the job.
          */
-        virtual bool render_job(const RenderingJob& job);
-        virtual void render_job_queue(std::queue<RenderingJob>& queue);
-        virtual void render_job_queue(std::map<float, RenderingJob, std::greater<>>& queue);
+        virtual bool render_job(const float& interpolate_alpha, const RenderingJob& job);
+        virtual void render_job_queue(const float& interpolate_alpha, std::queue<RenderingJob>& queue);
+        virtual void render_job_queue(const float& interpolate_alpha, std::map<float, RenderingJob, std::greater<>>& queue);
     };
 }
\ No newline at end of file
diff --git a/include/simpleengine/renderable.h b/include/simpleengine/renderable.h
index cf7446c..667c20b 100644
--- a/include/simpleengine/renderable.h
+++ b/include/simpleengine/renderable.h
@@ -14,6 +14,6 @@ namespace simpleengine {
         Renderable() = default;
         virtual ~Renderable() = default;
 
-        virtual void render() = 0;
+        virtual void render(const float& interpolate_alpha, const float& frame_time) = 0;
     };
 }
\ No newline at end of file
diff --git a/include/simpleengine/scene.h b/include/simpleengine/scene.h
index ec086fa..bda0945 100644
--- a/include/simpleengine/scene.h
+++ b/include/simpleengine/scene.h
@@ -9,6 +9,7 @@
 #include <memory>
 
 #include <GLFW/glfw3.h>
+#include <unordered_map>
 #include <vector>
 
 #include <entt/entt.hpp>
@@ -18,16 +19,21 @@ namespace simpleengine {
         class Entity;
     }
 
-    class Scene : public simpleengine::Event {
+    //class Scene : public simpleengine::Event {
+    class Scene : public simpleengine::Renderable {
     protected:
         entt::registry registry;
         std::shared_ptr<gfx::Renderer> renderer;
+
+        // Last transform matrixes for all entities.
+        std::unordered_map<uint32_t, glm::mat4> last_transforms;
     public:
         Scene(std::shared_ptr<gfx::Renderer> renderer);
 
         ecs::Entity create_entity();
 
         virtual void update(const float& delta_time) override;
+        virtual void render(const float& interpolate_alpha, const float& frame_time) override;
 
         virtual void destroy() override;
     };
diff --git a/resources/shaders/core/3d/fragment_core.glsl b/resources/shaders/core/3d/fragment_core.glsl
index cd76c7b..f7ffb44 100644
--- a/resources/shaders/core/3d/fragment_core.glsl
+++ b/resources/shaders/core/3d/fragment_core.glsl
@@ -26,7 +26,7 @@ struct Material {
 
     bool has_specular_map;
     sampler2D specular_map;
-    
+
     bool has_normal_map;
     sampler2D normal_map;
 
diff --git a/src/game.cpp b/src/game.cpp
index dc7d5ac..f158503 100644
--- a/src/game.cpp
+++ b/src/game.cpp
@@ -19,7 +19,7 @@
 
 simpleengine::Game::Game(int w, int h, const std::string& window_name, const int& gl_profile, const int& major_version,
         const int& minor_version, const bool& resizeable, const int& forward_compat) : window_resizeable(resizeable),
-        enable_vsync(true), fps_limit(-1) {
+        tps_accumulator(0.f) {
     initialize(gl_profile, major_version, minor_version, window_resizeable, forward_compat);
 
     // Create a window
@@ -45,6 +45,8 @@ simpleengine::Game::Game(int w, int h, const std::string& window_name, const int
     }
 
     enable_default_gl_options();
+
+    last_frame_time = std::chrono::high_resolution_clock::now();
 }
 
 void simpleengine::Game::enable_default_gl_options() const {
@@ -105,6 +107,10 @@ void simpleengine::Game::update_enabled_vsync() const {
     }
 }
 
+void simpleengine::Game::handle_input(const float& delta_time) {
+    // TODO
+}
+
 void simpleengine::Game::update(const float& delta_time) {
     handle_input(delta_time);
 
@@ -114,19 +120,15 @@ void simpleengine::Game::update(const float& delta_time) {
     }
 }
 
-void simpleengine::Game::handle_input(const float& delta_time) {
-    // TODO
-}
-
-void simpleengine::Game::render_window(const float& delta_time) {
+void simpleengine::Game::render_window(const float& interpolate_alpha, const float& delta_time) {
     glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
-    render_items(delta_time);
+    render_items(interpolate_alpha, delta_time);
 }
 
-void simpleengine::Game::render_items(const float& delta_time) {
+void simpleengine::Game::render_items(const float& interpolate_alpha, const float& delta_time) {
     for (const std::shared_ptr<Renderable>& renderable : renderable_events) {
-        renderable->render();
+        renderable->render(interpolate_alpha, delta_time);
     }
 }
 
@@ -155,12 +157,24 @@ int simpleengine::Game::run() {
     while (!glfwWindowShouldClose(window)) {
         // Get delta time first thing
         float delta_time = get_delta_time();
+        //std::cout << "Delta time: " << delta_time << std::endl;
 
         // Poll input events
         glfwPollEvents();
 
-        update(delta_time);
-        render_window(delta_time);
+        const double max_delta_time = 0.5;
+
+        tps_accumulator += delta_time;
+
+        while (tps_accumulator >= max_delta_time) {
+            update(max_delta_time);
+
+            tps_accumulator -= max_delta_time;
+        }
+
+        const double interpolate_alpha = tps_accumulator / max_delta_time;
+        
+        render_window(interpolate_alpha, delta_time);
 
         // End draw
         glfwSwapBuffers(window);
diff --git a/src/gfx/renderer.cpp b/src/gfx/renderer.cpp
index 47d099d..514ec33 100644
--- a/src/gfx/renderer.cpp
+++ b/src/gfx/renderer.cpp
@@ -13,11 +13,13 @@
 #include <glm/geometric.hpp>
 #include <stdexcept>
 
+#include <glm/gtx/string_cast.hpp>
+
 namespace simpleengine::gfx {
     void create_mesh_buffers(simpleengine::gfx::Mesh &mesh);
 
-    RenderingJob::RenderingJob(RenderingType rendering_type, gfx::Mesh &mesh, glm::mat4 position)
-        : rendering_type(rendering_type), rendering_mesh(&mesh), transform_mat(position) {}
+    RenderingJob::RenderingJob(RenderingType rendering_type, gfx::Mesh &mesh, glm::mat4 last_pos, glm::mat4 position)
+        : rendering_type(rendering_type), rendering_mesh(&mesh), last_transform_mat(last_pos), transform_mat(position) {}
 
     Renderer::Renderer(GLFWwindow *window, gfx::Shader shader, std::shared_ptr<Camera> camera)
         : window(window), shader(shader), camera(camera)/* , transparent_render_queue(CameraDistanceComparator(camera)) */ {}
@@ -50,8 +52,8 @@ namespace simpleengine::gfx {
         // std::sort()
     }
 
-    void Renderer::queue_job(RenderingType rendering_type, gfx::Mesh &mesh, glm::mat4 position) {
-        RenderingJob job(rendering_type, mesh, position);
+    void Renderer::queue_job(RenderingType rendering_type, gfx::Mesh &mesh, glm::mat4 last_position, glm::mat4 position) {
+        RenderingJob job(rendering_type, mesh, last_position, position);
 
         this->queue_job(job);
     }
@@ -135,10 +137,37 @@ namespace simpleengine::gfx {
         } */
     }
 
-    bool Renderer::render_job(const RenderingJob &job) {
+    glm::mat4 lerp(glm::mat4 a, glm::mat4 b, float alpha) {
+        //return a * (1.f - alpha) + b * alpha;
+        glm::quat rot0 = glm::quat_cast(a);
+        glm::quat rot1= glm::quat_cast(b);
+
+        glm::quat finalRot = glm::slerp(rot0, rot1, alpha);
+
+        glm::mat4 finalMat = glm::mat4_cast(finalRot);
+
+        finalMat[3] = a[3] * (1 - alpha) + b[3] * alpha;
+        
+        return finalMat;
+    }
+
+    bool Renderer::render_job(const float& interpolate_alpha, const RenderingJob &job) {
         Mesh *mesh = job.rendering_mesh;
 
-        shader.set_uniform_matrix_4f("u_transform_matrix", job.transform_mat);
+        /* glm::mat4 transform_mat = job.transform_mat * interpolate_alpha +
+            job.last_transform_mat * (1.f - interpolate_alpha); */
+
+        //glm::mat4 transform_mat = lerp(job.transform_mat, job.last_transform_mat, interpolate_alpha);
+        glm::mat4 transform_mat = lerp(job.last_transform_mat, job.transform_mat, interpolate_alpha);
+
+        std::cout << "Last transform: " << glm::to_string(job.last_transform_mat) << std::endl <<
+            "Current Transform: " << glm::to_string(job.transform_mat) << std::endl <<
+            "Lerp: " << glm::to_string(transform_mat) << std::endl << std::endl;
+
+        //std::cout << "Current: " << job.transform_mat[3]
+
+        shader.set_uniform_matrix_4f("u_transform_matrix", transform_mat);
+        //shader.set_uniform_matrix_4f("u_transform_matrix", job.transform_mat);
 
         std::optional<Material> &material = mesh->material;
 
@@ -196,12 +225,12 @@ namespace simpleengine::gfx {
         return true;
     }
 
-    void Renderer::render_job_queue(std::queue<RenderingJob> &rendering_queue) {
+    void Renderer::render_job_queue(const float& interpolate_alpha, std::queue<RenderingJob> &rendering_queue) {
         while (!rendering_queue.empty()) {
             // Get the job from the queue, we'll remove it after we render.
             RenderingJob &job = rendering_queue.front();
 
-            bool res = this->render_job(job);
+            bool res = this->render_job(interpolate_alpha, job);
 
             if (res) {
                 // Now we'll remove the job from the queue.
@@ -210,19 +239,19 @@ namespace simpleengine::gfx {
         }
     }
 
-    void Renderer::render_job_queue(std::map<float, RenderingJob, std::greater<>>& rendering_queue) {
+    void Renderer::render_job_queue(const float& interpolate_alpha, std::map<float, RenderingJob, std::greater<>>& rendering_queue) {
         // Render each job then clear the queue
         for (const auto& it : rendering_queue) {
-            this->render_job(it.second);
+            this->render_job(interpolate_alpha, it.second);
         }
         rendering_queue.clear();
     }
 
-    void Renderer::render() {
+    void Renderer::render(const float& interpolate_alpha, const float& frame_time) {
         check_if_initialized();
 
         // Render other (opaque) objects first 
-        render_job_queue(other_render_queue);
+        render_job_queue(interpolate_alpha, other_render_queue);
 
         // Render transparent objects
         std::map<float, RenderingJob, std::greater<>> transparent_jobs;
@@ -235,6 +264,6 @@ namespace simpleengine::gfx {
 
             transparent_render_queue.pop();
         }
-        render_job_queue(transparent_jobs);
+        render_job_queue(interpolate_alpha, transparent_jobs);
     }
 } // namespace simpleengine::gfx
\ No newline at end of file
diff --git a/src/scene.cpp b/src/scene.cpp
index d5e5540..875acd8 100644
--- a/src/scene.cpp
+++ b/src/scene.cpp
@@ -16,30 +16,37 @@ namespace simpleengine {
     }
 
     void Scene::update(const float& delta_time) {
+        // Rotate the model
+        registry.view<TransformComponent, RotatingComponent>().each([this, &delta_time](TransformComponent& transform, RotatingComponent& rotating) {
+            transform.rotate(rotating.rate * delta_time, rotating.rotation_axis);
+        });
+    }
+
+    void Scene::render(const float& interpolate_alpha, const float& frame_time) {
         // Is there a way these can be grouped?
-        registry.view<const TransformComponent, ModelComponent>().each([this](const TransformComponent& transform, ModelComponent& model_component) {
+        registry.view<TransformComponent, ModelComponent>().each([this](TransformComponent& transform, ModelComponent& model_component) {
             for (auto& mesh : model_component.model.meshes) {
                 auto rendering_type = gfx::RenderingType::RendType_OPAQUE;
                 if (mesh.material) {
                     rendering_type = mesh.material->rendering_type;
                 }
 
-                renderer->queue_job(gfx::RenderingJob(rendering_type, mesh, transform.transform_matrix));
+                renderer->queue_job(gfx::RenderingJob(rendering_type, mesh, transform.last_transform_matrix, transform.transform_matrix));
+                transform.last_transform_matrix = transform.transform_matrix; // Update last transform
             }
         });
 
-        registry.view<const TransformComponent, MeshComponent>().each([this](const TransformComponent& transform, MeshComponent& mesh_component) {
+        registry.view<TransformComponent, MeshComponent>().each([this](TransformComponent& transform, MeshComponent& mesh_component) {
             auto rendering_type = gfx::RenderingType::RendType_OPAQUE;
             if (mesh_component.mesh.material) {
                 rendering_type = mesh_component.mesh.material->rendering_type;
             }
 
-            renderer->queue_job(gfx::RenderingJob(rendering_type, mesh_component.mesh, transform.transform_matrix));
+            renderer->queue_job(gfx::RenderingJob(rendering_type, mesh_component.mesh, transform.last_transform_matrix, transform.transform_matrix));
+            transform.last_transform_matrix = transform.transform_matrix; // Update last transform
         });
 
-        registry.view<TransformComponent, RotatingComponent>().each([this, &delta_time](TransformComponent& transform, RotatingComponent& rotating) {
-            transform.rotate(rotating.rate * delta_time, rotating.rotation_axis);
-        });
+        renderer->render(interpolate_alpha, frame_time);
     }
 
     void Scene::destroy() {