diff --git a/src/engine.c b/src/engine.c
index bdf201a..d3b6e14 100644
--- a/src/engine.c
+++ b/src/engine.c
@@ -1,4 +1,5 @@
 #include "engine.h"
+#include "world.h"
 #include "corelib/assets.h"
 #include "corelib/render.h"
 #include "corelib/input.h"
@@ -47,7 +48,8 @@ int _engine_run() {
 		.running = 1,
 	};
 
-	load_game();
+	input_init();
+	world_clear();
 	start_game();
 	
 	timespec_get(&start_last_frame, TIME_UTC);
@@ -58,10 +60,13 @@ int _engine_run() {
 		if(next_time.tv_nsec < start_last_frame.tv_nsec) _delta_time = 0;
 		start_last_frame = next_time;
 		_handle_events();
+		update_input();
 		_render_mode = 1;
 		update_ui();
 		_render_mode = 0;
+		update_objects();	// update world objects
 		update_game();
+		draw_objects();		// draw world objects
 		swap_buffer();
 	}
 	return 0;
diff --git a/src/game.c b/src/game.c
index c2feec3..95016d2 100644
--- a/src/game.c
+++ b/src/game.c
@@ -1,6 +1,5 @@
 #include "engine.h"
 #include "world.h"
-#include "player.h"
 #include "corelib/input.h"
 #include "corelib/render.h"
 #include "corelib/assets.h"
@@ -8,83 +7,45 @@
 #include "SDL2/SDL_mouse.h"
 #include "SDL2/SDL_scancode.h"
 
-int dragging = 0;
-int drawing = 0;
-spritesheet_t world_sheet;
-
 void on_quit_key(int down) {
+	// Q is pressed or released
 	if(down) {
+		// stop running when Q is pressed
 		g_context.running = 0;
 	}
 }
 
+void on_horizontal(int axis) {
+	// when A or D is pressed or released
+}
+
+void on_vertical(int axis) {
+	// W or S is pressed or released
+}
+
 void on_click(int down) {
-	drawing = down;
-}
-
-void on_erase(int down) {
-	drawing = -down;
-}
-
-void on_drag_world(float dx, float dy) {
-	if(dragging) {
-		g_active_view.x -= dx * g_active_view.width;
-		g_active_view.y -= dy * g_active_view.width;
-	}
-}
-
-void on_middle_mouse(int down) {
-	dragging = down;
-}
-
-void on_debug_frame(int down) {
-	if(down) {
-		d_debug_next_frame = 1;
-	}
-}
-
-
-void on_button_zoom(int axis) {
-	if(axis != 0) {
-		g_active_view.width += axis;
-	}
-}
-
-void on_scroll_zoom(float delta) {
-	g_active_view.width -= delta * 0.5f;
-}
-
-void load_game() {
-	world_sheet = make_spritesheet("tileset.png", 189, 189);
-
-	input_init();
-	world_clear();
-	add_key_listener(SDL_SCANCODE_UNKNOWN, SDL_SCANCODE_Q, &on_quit_key);
-	add_key_listener(SDL_SCANCODE_UNKNOWN, SDL_SCANCODE_TAB, &on_debug_frame);
-	add_key_listener(SDL_SCANCODE_MINUS, SDL_SCANCODE_EQUALS, &on_button_zoom);
-	add_mouse_button_listener(SDL_BUTTON_LMASK, &on_click);
-	add_mouse_button_listener(SDL_BUTTON_RMASK, &on_erase);
-	add_mouse_button_listener(SDL_BUTTON_MMASK, &on_middle_mouse);
-	add_mouse_listener(&on_drag_world);
-	add_scroll_listener(&on_scroll_zoom);
-
-	create_player();
+	// when the left mouse button is pressed down
+	// float mouse_x, mouse_y;
+	// mouse_world_position(&mouse_x, &mouse_y);
 }
 
 void start_game() {
+	// called when the game first run
 	g_active_view.width = 21;
+	add_key_listener(SDL_SCANCODE_UNKNOWN, SDL_SCANCODE_Q, &on_quit_key);
+	add_key_listener(SDL_SCANCODE_S, SDL_SCANCODE_W, &on_horizontal);
+	add_key_listener(SDL_SCANCODE_A, SDL_SCANCODE_D, &on_vertical);
+	add_mouse_button_listener(SDL_BUTTON_LMASK, &on_click);
 }
 
 void update_game() {
-	if(drawing == 1) {
-		drawing = 2;
-	}
-	update_objects();
-	draw_objects();
+	// called every frame,
+	// render calls made in this function will be in *world* space
 }
 
 void update_ui() {
-	update_input();
+	// called every frame,
+	// render calls made in this function will be in *screen* space
 }
 
 void game_exit() {}