Implement hot reloading

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;
-
-void game_init(int argc, char *argv[], void *mem, SDL_Renderer *renderer);
-void game_teardown(void *mem);
-
-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);
+#define X(hook) hook##_t hook;
+HOOKS_XLIST
+#undef X
+#endif
 
 #endif