From 4ba85c9e79ae8cbac13546206a757d2de0f4d3ce Mon Sep 17 00:00:00 2001
From: lisyarus <lisyarus@gmail.com>
Date: Wed, 3 Mar 2021 18:03:40 +0300
Subject: [PATCH] App uses a scene stack & owns scenes

---
 libs/app/include/psemek/app/app.hpp |  3 ++-
 libs/app/source/app.cpp             | 36 +++++++++++++++++++++--------
 2 files changed, 28 insertions(+), 11 deletions(-)

diff --git a/libs/app/include/psemek/app/app.hpp b/libs/app/include/psemek/app/app.hpp
index 9f5a07ca..7c4d9c2b 100644
--- a/libs/app/include/psemek/app/app.hpp
+++ b/libs/app/include/psemek/app/app.hpp
@@ -29,7 +29,8 @@ namespace psemek::app
 		void poll_events();
 		void run();
 
-		scene * set_scene(scene * s);
+		void push_scene(std::unique_ptr<scene> s);
+		std::unique_ptr<scene> pop_scene();
 
 		void show_cursor(bool show);
 		void vsync(bool on);
diff --git a/libs/app/source/app.cpp b/libs/app/source/app.cpp
index 4eafd637..d92a3038 100644
--- a/libs/app/source/app.cpp
+++ b/libs/app/source/app.cpp
@@ -5,6 +5,8 @@
 
 #include <SDL2/SDL.h>
 
+#include <vector>
+
 namespace psemek::app
 {
 
@@ -18,7 +20,7 @@ namespace psemek::app
 		SDL_Window * window = nullptr;
 		SDL_GLContext gl_context = nullptr;
 
-		scene * current_scene = nullptr;
+		std::vector<std::unique_ptr<scene>> scene_stack;
 
 		bool running = false;
 
@@ -39,8 +41,8 @@ namespace psemek::app
 
 		scene * get_scene()
 		{
-			if (current_scene)
-				return current_scene;
+			if (!scene_stack.empty())
+				return scene_stack.back().get();
 			return parent;
 		}
 	};
@@ -199,36 +201,50 @@ namespace psemek::app
 	{
 		SDL_ShowWindow(impl().window);
 		impl().running = true;
-		if (impl().current_scene == nullptr)
+		if (impl().get_scene() == this)
 			on_scene_enter(this);
 		while (running())
 		{
 			poll_events();
 
-			auto handler = impl().get_scene();
+			auto handler = [this]{ return impl().get_scene(); };
 
 			if (!impl().had_initial_resize)
 			{
 				int w, h;
 				SDL_GetWindowSize(impl().window, &w, &h);
 				impl().had_initial_resize = true;
-				handler->on_resize(w, h);
+				handler()->on_resize(w, h);
 			}
 			if (!running()) break;
-			handler->update();
-			handler->present();
+			handler()->update();
+			handler()->present();
 
 			SDL_GL_SwapWindow(impl().window);
 		}
 		impl().get_scene()->on_scene_exit();
 	}
 
-	scene * app::set_scene(scene * s)
+	void app::push_scene(std::unique_ptr<scene> s)
 	{
 		impl().get_scene()->on_scene_exit();
 
 		impl().had_initial_resize = false;
-		std::swap(s, impl().current_scene);
+		impl().scene_stack.push_back(std::move(s));
+
+		impl().get_scene()->on_scene_enter(this);
+	}
+
+	std::unique_ptr<scene> app::pop_scene()
+	{
+		if (impl().scene_stack.empty())
+			return nullptr;
+
+		impl().get_scene()->on_scene_exit();
+
+		impl().had_initial_resize = false;
+		auto s = std::move(impl().scene_stack.back());
+		impl().scene_stack.pop_back();
 
 		impl().get_scene()->on_scene_enter(this);