Some debug code cleanup, change the format for the mod buffer key.

data.lua

@@ -49,7 +49,7 @@ function init_data()
    }
 
    -- initialize a ring buffer of changed positions. In use, this will be keyed
-   -- using strings of the form mod_buffer["x+y"], using absolute world
+   -- using strings of the form mod_buffer["x:y"], using absolute world
    -- coordinates. this is to flatten the buffer so that #mod_cache is useful
    -- for checking against max_mod_entries.
    max_mod_entries = 4096
@@ -57,13 +57,23 @@ function init_data()
 end
 
 -- x and y are global coords
+function get_mod_key(x, y)
+   return tostr(x) .. ":" .. tostr(y)
+end
+
+-- x and y are map-local coords
 function write_map_change(new_sprite, x, y)
    local global_x, global_y = calculate_world_pos(x, y)
    if #mod_buffer >= max_mod_entries then
-      -- todo: make the buffer ring
+      cull_mod_buffer()
    end
 
-   mod_buffer[tostr(global_x) .. "+" .. tostr(global_y)] = new_sprite
+   mod_buffer[get_mod_key(global_x, global_y)] = new_sprite
+end
+
+function cull_mod_buffer()
+   -- we cull 10% of the mod buffer at a time
+   -- todo: implement this
 end
 
 function calculate_world_pos(x, y)