feat: add play / editor mode

destrum/src/App.cpp

@@ -7,7 +7,10 @@
 
 #include <destrum/FS/AssetFS.h>
 #include <destrum/Graphics/Resources/FontCache.h>
+#include <destrum/ObjectModel/GameObject.h>
+#include <destrum/Scene/Scene.h>
 #include <destrum/Scene/SceneManager.h>
+#include <destrum/Serialization/SceneSerializer.h>
 #include <destrum/Util/DeltaTime.h>
 
 #include "imgui.h"
@@ -67,6 +70,8 @@ void App::init(const AppParams& params)
 
         customInitStarted = true;
         customInit();
+        playing = !params.startInEditMode;
+        SceneManager::GetInstance().SetPlaying(playing);
         cleanedUp = false;
     } catch (...) {
         try {
@@ -179,6 +184,11 @@ if (!isRunning) break;
             continue;
         }
 
+        if (InputManager::GetInstance().WasKeyPressed(SDL_SCANCODE_F5))
+        {
+            playModeToggleRequested = true;
+        }
+
         // Consume SDL events before updating the base camera so held and
         // newly pressed inputs are applied in the same frame.
         camera.Update(dt);
@@ -239,6 +249,14 @@ if (!isRunning) break;
             imguiPass.endFrame();
         }
 
+        if (playModeToggleRequested)
+        {
+            ZoneScopedN("Play Mode Toggle");
+            playModeToggleRequested = false;
+            applyPlayModeToggle();
+            accumulator = 0.0f;
+        }
+
         {
             ZoneScopedN("FixedUpdate");
 
@@ -406,9 +424,111 @@ void App::drawWindowsMenu()
         ImGui::EndMenu();
     }
 
+    drawPlayControls();
+
     ImGui::EndMainMenuBar();
 }
 
+void App::drawPlayControls()
+{
+    const char* state = playing ? "PLAYING" : "EDIT";
+    const char* action = playing ? "Stop (F5)" : "Play (F5)";
+    const ImGuiStyle& style = ImGui::GetStyle();
+    const float width = ImGui::CalcTextSize(state).x + ImGui::CalcTextSize(action).x +
+                        style.ItemSpacing.x * 2.0f + style.FramePadding.x * 2.0f;
+
+    // Centered like Godot's run buttons, unless the menus already reach past the middle
+    ImGui::SetCursorPosX(std::max(ImGui::GetCursorPosX(), (ImGui::GetWindowWidth() - width) * 0.5f));
+    ImGui::TextColored(playing ? ImVec4{0.4f, 0.9f, 0.4f, 1.0f} : ImVec4{0.7f, 0.7f, 0.7f, 1.0f}, "%s", state);
+    if (ImGui::MenuItem(action))
+    {
+        playModeToggleRequested = true;
+    }
+}
+
+void App::applyPlayModeToggle()
+{
+    if (playing)
+    {
+        exitPlayMode();
+    }
+    else
+    {
+        enterPlayMode();
+    }
+}
+
+bool App::enterPlayMode()
+{
+    auto& sceneManager = SceneManager::GetInstance();
+    if (sceneManager.GetActiveScenes().empty())
+    {
+        spdlog::error("Cannot enter play mode without an active scene");
+        return false;
+    }
+
+    const std::shared_ptr<Scene> scene = sceneManager.GetActiveScenes().front();
+    auto snapshot = SceneSerializer::Capture(*scene);
+    if (!snapshot)
+    {
+        spdlog::error("Cannot enter play mode, scene \"{}\" could not be saved", scene->GetName());
+        return false;
+    }
+    if (const GameObject* selected = scene->GetSelectedObject())
+    {
+        (*snapshot)["selected"] = selected->GetId();
+    }
+
+    // Play runs the scene as it would load from disk, so nothing the editor did to the live objects
+    // (started components, unsaved runtime state) leaks into the game
+    if (!SceneSerializer::LoadFromJson(*scene, *snapshot))
+    {
+        spdlog::error("Cannot enter play mode, scene \"{}\" did not load back", scene->GetName());
+        return false;
+    }
+
+    editSnapshot = std::move(snapshot);
+    editScene = scene;
+    playing = true;
+    sceneManager.SetPlaying(true);
+    spdlog::info("Entered play mode");
+    onPlayModeChanged(true);
+    return true;
+}
+
+void App::exitPlayMode()
+{
+    auto& sceneManager = SceneManager::GetInstance();
+    playing = false;
+    sceneManager.SetPlaying(false);
+    InputManager::GetInstance().SetMouseCaptured(false);
+
+    const std::shared_ptr<Scene> scene = editScene.lock();
+    if (scene && editSnapshot)
+    {
+        const auto& scenes = sceneManager.GetScenes();
+        const auto it = std::find(scenes.begin(), scenes.end(), scene);
+        if (it != scenes.end() && (sceneManager.GetActiveScenes().empty() ||
+                                   sceneManager.GetActiveScenes().front() != scene))
+        {
+            sceneManager.SwitchScene(static_cast<int>(std::distance(scenes.begin(), it)));
+        }
+        if (!SceneSerializer::LoadFromJson(*scene, *editSnapshot))
+        {
+            spdlog::error("Could not restore scene \"{}\" to its state before play mode", scene->GetName());
+        }
+    }
+    else
+    {
+        spdlog::warn("The scene play mode started from no longer exists, nothing to restore");
+    }
+
+    editSnapshot.reset();
+    editScene.reset();
+    spdlog::info("Exited play mode");
+    onPlayModeChanged(false);
+}
+
 void App::drawPhysicsPanel(float dt, float fixedDt, float accumulator)
 {
     if (!ImGui::Begin("Physics", &m_DebugWindows.physics))