feat: add runtime play tick and play-mode scene editing semantics

engine/CMakeLists.txt

@@ -377,9 +377,11 @@ add_library(XCEngine STATIC
     # Scene
     ${CMAKE_CURRENT_SOURCE_DIR}/include/XCEngine/Scene/Scene.h
     ${CMAKE_CURRENT_SOURCE_DIR}/include/XCEngine/Scene/SceneRuntime.h
+    ${CMAKE_CURRENT_SOURCE_DIR}/include/XCEngine/Scene/RuntimeLoop.h
     ${CMAKE_CURRENT_SOURCE_DIR}/include/XCEngine/Scene/SceneManager.h
     ${CMAKE_CURRENT_SOURCE_DIR}/src/Scene/Scene.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/Scene/SceneRuntime.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/src/Scene/RuntimeLoop.cpp
     ${CMAKE_CURRENT_SOURCE_DIR}/src/Scene/SceneManager.cpp
 
     # Platform

engine/include/XCEngine/Scene/RuntimeLoop.h

@@ -0,0 +1,45 @@
+#pragma once
+
+#include <XCEngine/Scene/SceneRuntime.h>
+
+#include <cstdint>
+
+namespace XCEngine {
+namespace Components {
+
+class RuntimeLoop {
+public:
+    struct Settings {
+        float fixedDeltaTime = 1.0f / 50.0f;
+        float maxFrameDeltaTime = 0.1f;
+        uint32_t maxFixedStepsPerFrame = 4;
+    };
+
+    explicit RuntimeLoop(Settings settings = {});
+
+    void SetSettings(const Settings& settings);
+    const Settings& GetSettings() const { return m_settings; }
+
+    void Start(Scene* scene);
+    void Stop();
+
+    void Tick(float deltaTime);
+    void Pause();
+    void Resume();
+    void StepFrame();
+
+    bool IsRunning() const { return m_sceneRuntime.IsRunning(); }
+    bool IsPaused() const { return m_paused; }
+    Scene* GetScene() const { return m_sceneRuntime.GetScene(); }
+    float GetFixedAccumulator() const { return m_fixedAccumulator; }
+
+private:
+    SceneRuntime m_sceneRuntime;
+    Settings m_settings = {};
+    float m_fixedAccumulator = 0.0f;
+    bool m_paused = false;
+    bool m_stepRequested = false;
+};
+
+} // namespace Components
+} // namespace XCEngine

engine/src/Scene/RuntimeLoop.cpp

@@ -0,0 +1,100 @@
+#include "Scene/RuntimeLoop.h"
+
+#include <algorithm>
+
+namespace XCEngine {
+namespace Components {
+
+namespace {
+
+RuntimeLoop::Settings SanitizeSettings(RuntimeLoop::Settings settings) {
+    if (settings.fixedDeltaTime <= 0.0f) {
+        settings.fixedDeltaTime = 1.0f / 50.0f;
+    }
+    if (settings.maxFrameDeltaTime < 0.0f) {
+        settings.maxFrameDeltaTime = 0.0f;
+    }
+    if (settings.maxFixedStepsPerFrame == 0) {
+        settings.maxFixedStepsPerFrame = 1;
+    }
+    return settings;
+}
+
+} // namespace
+
+RuntimeLoop::RuntimeLoop(Settings settings)
+    : m_settings(SanitizeSettings(settings)) {
+}
+
+void RuntimeLoop::SetSettings(const Settings& settings) {
+    m_settings = SanitizeSettings(settings);
+}
+
+void RuntimeLoop::Start(Scene* scene) {
+    m_fixedAccumulator = 0.0f;
+    m_paused = false;
+    m_stepRequested = false;
+    m_sceneRuntime.Start(scene);
+}
+
+void RuntimeLoop::Stop() {
+    m_sceneRuntime.Stop();
+    m_fixedAccumulator = 0.0f;
+    m_paused = false;
+    m_stepRequested = false;
+}
+
+void RuntimeLoop::Tick(float deltaTime) {
+    if (!IsRunning()) {
+        return;
+    }
+
+    if (m_paused && !m_stepRequested) {
+        return;
+    }
+
+    const float clampedDeltaTime = std::clamp(deltaTime, 0.0f, m_settings.maxFrameDeltaTime);
+    m_fixedAccumulator += clampedDeltaTime;
+
+    uint32_t fixedStepsExecuted = 0;
+    while (m_fixedAccumulator >= m_settings.fixedDeltaTime &&
+           fixedStepsExecuted < m_settings.maxFixedStepsPerFrame) {
+        m_sceneRuntime.FixedUpdate(m_settings.fixedDeltaTime);
+        m_fixedAccumulator -= m_settings.fixedDeltaTime;
+        ++fixedStepsExecuted;
+    }
+
+    m_sceneRuntime.Update(clampedDeltaTime);
+    m_sceneRuntime.LateUpdate(clampedDeltaTime);
+    m_stepRequested = false;
+}
+
+void RuntimeLoop::Pause() {
+    if (!IsRunning()) {
+        return;
+    }
+
+    m_paused = true;
+    m_stepRequested = false;
+}
+
+void RuntimeLoop::Resume() {
+    if (!IsRunning()) {
+        return;
+    }
+
+    m_paused = false;
+    m_stepRequested = false;
+}
+
+void RuntimeLoop::StepFrame() {
+    if (!IsRunning()) {
+        return;
+    }
+
+    m_paused = true;
+    m_stepRequested = true;
+}
+
+} // namespace Components
+} // namespace XCEngine