Add interactability with some map objects, and store changed map tiles in a buffer for persistence.

player.lua

@@ -49,6 +49,10 @@ function handle_input()
    local new_pos_x, new_pos_y = camera_pos_x, camera_pos_y
    local new_ppos_x, new_ppos_y = player_pos_x, player_pos_y
 
+   if btnp"4" then
+      interact()
+   end
+
    if btnp"0" or btnp"1" or btnp"2" or btnp"3" then
       if btnp"0" then
          new_pos_x -= 1 -- move left
@@ -121,6 +125,22 @@ function can_interact()
    return nil, nil
 end
 
+function interact()
+   -- get the position to interact with
+   local x, y = can_interact()
+   if (x == nil or y == nil) return
+
+   local sprite = mget(x, y)
+   local data = object_interaction_map[sprite]
+   -- todo: figure out playing sound effects, animation?
+
+   -- modify the rendered tile
+   mset(x, y, data.replacement)
+
+   -- and write the change to the buffer
+   write_map_change(data.replacement, x, y)
+end
+
 -- returns x,y representing the map-local position the player is facing.
 function get_position_facing()
    return camera_pos_x+8+facing_h, camera_pos_y+8+facing_v