add much-needed optimizations and enhance the snake example game

src/engine/engine_init.c

@@ -65,6 +65,11 @@ engine_sdl_init_renderer(
 		return RCODE_FAILURE;
 	}
 
+	// enable VSync
+	if (!SDL_SetRenderVSync(state->renderer, 1)) {
+	    eprintf("SDL_SetRenderVSync failed: %s\n", SDL_GetError());
+	}
+
 	return RCODE_SUCCESS;
 }
 
@@ -127,9 +132,16 @@ engine_init(
 ) {
 	internal_state = (engine_internal_state_t *)
 		malloc(sizeof(engine_internal_state_t));
+	if (internal_state == NULL) {
+		return RCODE_FAILURE;
+	}
 
 	game_state = (game_state_t *)
 		malloc(sizeof(game_state_t));
+	if (game_state == NULL) {
+		free(internal_state);
+		return RCODE_FAILURE;
+	}
 
 	internal_state->engine_poll_events
 		= engine_poll_events;
@@ -138,11 +150,22 @@ engine_init(
 		= engine_update_framebuffer;
 
 	internal_state->sdl_state = engine_sdl_init();
+	if (internal_state->sdl_state == NULL) {
+		free(internal_state);
+		free(game_state);
+		return RCODE_FAILURE;
+	}
 
 	game_state->is_running = true;
+	game_state->framebuffer_dirty = true;
+	game_state->dirty_rect = (SDL_Rect) {
+	    .x = 0,
+	    .y = 0,
+	    .w = game_state->width,
+	    .h = game_state->height
+	};
 	game_state->width = internal_state->sdl_state->width;
 	game_state->height = internal_state->sdl_state->height;
 
-	return (game_state == NULL || internal_state == NULL) 
-		? RCODE_FAILURE : RCODE_SUCCESS;
+	return RCODE_SUCCESS;
 }