Implement hot reloading

CMakeLists.txt

@@ -5,6 +5,7 @@ project(epec-mcu-emulator LANGUAGES C)
 option(WERROR "Treat warnings as errors" OFF)
 option(UBSAN "Enable undefined behaviour sanitizer" OFF)
 option(PERFMON "Monitor performance of game code" ON)
+option(HOTRELOAD "Enable hot reloading of game code" OFF)
 
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 
@@ -19,6 +20,9 @@ macro(set_default_target_options target)
 	target_compile_options(${target} PRIVATE -fsanitize=undefined)
 	target_link_options(${target} PRIVATE -fsanitize=undefined)
   endif()
+  if(${HOTRELOAD})
+	target_compile_definitions(engine PRIVATE HOTRELOAD)
+  endif()
 endmacro()
 
 add_custom_target(format
@@ -40,3 +44,9 @@ find_package(SDL2_image REQUIRED)
 
 add_subdirectory(engine)
 add_subdirectory(game)
+
+# Really this should be in engine/CMakeLists.txt, but it has to go
+# after the declaration of the game target.
+if(${HOTRELOAD})
+  target_compile_definitions(engine PRIVATE GAMELIB=\"$<TARGET_FILE:game>\")
+endif()

README

@@ -13,4 +13,16 @@ The build is handled with CMake (version 3.10 or later):
 The path to a directory containing the assets must be passed on the
 command line to run the game:
 
-   build/app/game ASSETS-DIR
+   build/game/game ASSETS-DIR
+
+
+							Hot Reloading
+
+The engine supports hot reloading of the game code via the F5 key; set
+the HOTRELOAD option on in CMake to enable it. You also have to run an
+executable built from the engine rather than the game if using this
+feature.
+
+	cmake -B build -D HOTRELOAD=ON
+	cmake --build build
+	build/engine/engine assets/

engine/CMakeLists.txt

@@ -1,6 +1,11 @@
-add_library(engine engine.c)
+if(${HOTRELOAD})
+  add_executable(engine engine.c)
+else()
+  add_library(engine SHARED engine.c)
+endif()
 set_default_target_options(engine)
 target_include_directories(engine PUBLIC include)
 if(${PERFMON})
   target_compile_definitions(engine PRIVATE PERFMON)
 endif()
+target_link_libraries(engine PRIVATE SDL2::SDL2)

engine/engine.c

@@ -6,6 +6,7 @@
 #include "engine_hooks.h"
 
 #include <assert.h>
+#include <dlfcn.h>
 #include <stdatomic.h>
 #include <stdbool.h>
 #include <stdlib.h>
@@ -25,8 +26,44 @@ typedef struct {
 	double max_start, max_evt, max_update, max_render, max_total;
 } perf_t;
 
+#ifdef HOTRELOAD
+static void *game_lib;
+static engineconf_t game_conf;
+
+#define X(hook) static hook##_t *hook;
+HOOKS_XLIST
+#undef X
+
+static void load_game_lib(void)
+{
+	bool firstload = game_lib == NULL;
+	if (!firstload)
+		dlclose(game_lib);
+
+	game_lib = dlopen(GAMELIB, RTLD_NOW);
+	assert(game_lib);
+
+	// We're copying this rather than using it as a pointer so that
+	// the syntax to use it with/without hot reloading is the same.
+	engineconf_t *conf = (engineconf_t *)dlsym(game_lib, "game_conf");
+	if (!firstload)
+		assert(conf->memsize == game_conf.memsize);
+	memcpy(&game_conf, conf, sizeof(engineconf_t));
+
+#define X(hook)	  \
+	hook = (hook##_t *)dlsym(game_lib, #hook); \
+	assert(hook);
+	HOOKS_XLIST
+#undef X
+}
+#endif
+
 int main(int argc, char *argv[])
 {
+#ifdef HOTRELOAD
+	load_game_lib();
+#endif
+
 	int err = SDL_Init(SDL_INIT_VIDEO);
 	assert(0 == err);
 
@@ -56,6 +93,10 @@ int main(int argc, char *argv[])
 		// Handle all events currently in queue
 		SDL_Event evt;
 		while (SDL_PollEvent(&evt)) {
+#ifdef HOTRELOAD
+			if (evt.type == SDL_KEYDOWN && evt.key.keysym.sym == SDLK_F5)
+				load_game_lib();
+#endif
 			if (game_evt(gamemem, &evt) != GAMESTATUS_OK)
 				goto quit;
 		}

engine/include/engine_hooks.h

@@ -21,14 +21,28 @@ typedef enum {
 	GAMESTATUS_QUIT,
 } gamestatus_t;
 
+typedef void
+game_init_t(int argc, char *argv[], void *mem, SDL_Renderer *renderer);
+typedef void game_teardown_t(void *mem);
+
+typedef gamestatus_t game_evt_t(void *mem, const SDL_Event *evt);
+typedef gamestatus_t game_update_t(void *mem, double dt);
+
+typedef void
+game_render_t(const void *mem, SDL_Renderer *renderer, long unsigned t);
+
+#define HOOKS_XLIST \
+	X(game_init) \
+	X(game_teardown) \
+	X(game_evt) \
+	X(game_update) \
+	X(game_render)
+
+#ifndef HOTRELOAD
 extern const engineconf_t game_conf;
-
+#define X(hook) hook##_t hook;
-void game_init(int argc, char *argv[], void *mem, SDL_Renderer *renderer);
+HOOKS_XLIST
-void game_teardown(void *mem);
+#undef X
-
+#endif
-gamestatus_t game_evt(void *mem, const SDL_Event *evt);
-gamestatus_t game_update(void *mem, double dt);
-
-void game_render(const void *mem, SDL_Renderer *renderer, long unsigned t);
 
 #endif

game/CMakeLists.txt

@@ -1,12 +1,17 @@
-add_executable(game main.c)
+if(${HOTRELOAD})
+  add_library(game SHARED main.c)
+  get_target_property(ENGINE_INCLUDES engine INCLUDE_DIRECTORIES)
+  target_include_directories(game PRIVATE ${ENGINE_INCLUDES})
+else()
+  add_executable(game main.c)
+  target_link_libraries(game PRIVATE engine)
+endif()
 set_default_target_options(game)
 target_include_directories(game PUBLIC include)
 
 target_link_libraries(game PRIVATE
-  engine
   m
   LibXml2::LibXml2
   SDL2::SDL2
-  SDL2::SDL2main
   SDL2_image::SDL2_image
 )