diff --git a/debug.lua b/debug.lua
index 92d5d32..b433591 100644
--- a/debug.lua
+++ b/debug.lua
@@ -40,7 +40,7 @@ function debug_print()
 end
 
 function debug_print_res()
-   clip(70, 0, 16, 24)
+   clip(70, 0, 32, 24)
    print(stat(0), 70, 0, 15)
    print(stat(1), 70, 8, 15)
    print(stat(9) .. " / " .. stat(8), 70, 16, 15)
@@ -54,15 +54,15 @@ function debug_print_sfx()
 end
 
 function debug_print_map()
-   clip(24, 0, 32, 24)
-   print(camera_pos_x .. " " .. camera_pos_y, 24, 0, 15)
-   print(player_pos_x .. " " .. player_pos_y, 24, 8, 15)
-   print(get_biome_name(player_pos_x, player_pos_y), 24, 16, 15)
+   clip(24, 0, 32, 16)
+   print(player_x .. " " .. player_y, 24, 0, 15)
+   print(get_biome_name(player_x, player_y), 24, 8, 15)
    clip()
 end
 
 function debug_print_mod_buffer()
    clip(0, 0, 16, 128)
+   rectfill(0,0,16,128,0)
    for k,v in pairs(mod_buffer) do
       print(k .. ": " .. tostr(v))
    end
diff --git a/main.lua b/main.lua
index 928abf1..8616ed4 100644
--- a/main.lua
+++ b/main.lua
@@ -1,38 +1,18 @@
 function _init()
    init_sound""
    init_world""
-   init_player(32, 32)
+   init_player""
    init_debug""
 end
 
 
 function _update()
    handle_input""
---   handle_map_update""
 end
 
 function _draw()
    cls""
-   -- the screen is 128x128 pixels, so it fits 16x16 sprites
-   --   map(camera_pos_x, camera_pos_y, 0, 0, 16, 16)
-   draw_world_segment(player_pos_x, player_pos_y)
+   draw_world(player_x, player_y)
    draw_player""
    debug_print""
 end
-
--- decide whether we need to regenerate the map.
--- if so, call generate_map appropriately and reset coordinates.
-function handle_map_update()
-   if out_of_bounds(camera_pos_x, camera_pos_y) then
-      -- out_of_bounds() checks all screen bounds
-      -- we need to regenerate the map, so we generate a map chunk that
-      -- places the player in the middle of it.
-      generate_map(player_pos_x-32, player_pos_y-32)
-      camera_pos_x, camera_pos_y = 24, 24
-   end
-end
-
-function out_of_bounds(pos_x, pos_y)
-   return pos_x < 0 or pos_x > 48 or
-      pos_y < 0 or pos_y > 48
-end
diff --git a/player.lua b/player.lua
index a4a707c..920e6f8 100644
--- a/player.lua
+++ b/player.lua
@@ -2,24 +2,19 @@
 -- Larger sprites will probably work for objects, but not for the player.
 --
 -- exported variables:
---   player_pos_[xy] # absolute position of the player on the 'world map'
---   camera_pos_[xy] # Represents top-left position of the pico-8 camera on
---                   # the pico-8 map
---   facing_[vh]     # Current facing of the player. Values of
---                   #   each element can be -1 (up or left), 0 (neutral),
---                   #   or 1 (down or right)
+--   player_[xy] # position of the player on the 'world map'
+--   facing_[vh] # Current facing of the player. Values of
+--               #   each element can be -1 (up or left), 0 (neutral),
+--               #   or 1 (down or right)
 --
 -- functions:
---   init_player(x,y) # call this in _init(). Sets player starting position,
---                    #   assumes the top-left of the pico-8 map is currently
---                    #   world position 0,0
---   handle_input()   # call in _update() to handle movement key presses.
---                    #   Assumes any sprite with flag 0 set is an obstacle.
---   draw_player()    # call in _draw(). Draws the player sprite.
+--   init_player()  # call this in _init().
+--   handle_input() # call in _update() to handle movement key presses.
+--                  #   Assumes any sprite with flag 0 set is an obstacle.
+--   draw_player()  # call in _draw(). Draws the player sprite.
 
-function init_player(start_pos_x, start_pos_y)
-   player_pos_x, player_pos_y = start_pos_x, start_pos_y
-   camera_pos_x, camera_pos_y = start_pos_x-8, start_pos_y-8
+function init_player()
+   player_x, player_y = 0, 0
 
    facing_v = 1
    facing_h = 0
@@ -46,8 +41,7 @@ end
 
 
 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
+   local new_x, new_y = player_x, player_y
 
    if btnp"4" then
       interact()
@@ -55,13 +49,11 @@ function handle_input()
 
    if btnp"0" or btnp"1" or btnp"2" or btnp"3" then
       if btnp"0" then
-         new_pos_x -= 1 -- move left
-         new_ppos_x -= 1
+         new_x -= 1 -- move left
          facing_h = 0xffff
       end
       if btnp"1" then
-         new_pos_x += 1 -- move right
-         new_ppos_x += 1 -- move right
+         new_x += 1 -- move right
          facing_h = 1
       end
       if not (btnp"0" or btnp"1") then
@@ -69,13 +61,11 @@ function handle_input()
       end
 
       if btnp"2" then
-         new_pos_y -= 1 -- move up
-         new_ppos_y -= 1 -- move up
+         new_y -= 1 -- move up
          facing_v = 0xffff
       end
       if btnp"3" then
-         new_pos_y += 1 -- move down
-         new_ppos_y += 1 -- move down
+         new_y += 1 -- move down
          facing_v = 1
       end
       if not (btnp"2" or btnp"3") then
@@ -83,9 +73,9 @@ function handle_input()
       end
    end
 
-   if legal_move(new_pos_x, new_pos_y) then
-      camera_pos_x, camera_pos_y = new_pos_x, new_pos_y
-      player_pos_x, player_pos_y = new_ppos_x, new_ppos_y
+   -- note that facing always changes, even if we can't move to the new location
+   if legal_move(new_x, new_y) then
+      player_x, player_y = new_x, new_y
    end
 end
 
@@ -102,52 +92,48 @@ function draw_player()
    -- todo: introduce the concept of an inventory here
 end
 
--- uses global variables instead of arguments
--- returns x,y for the map-local coordinates of the interactable object
+-- returns x,y as the coordinates of the interactable object
 -- nil,nil if nothing to interact with
+-- NB: this function calls get_tile() from world.lua
 function can_interact()
    -- flag 1 represents an interactable (read: destructible) sprite.
-   -- need a map of destructible map objects, appropriate sfx, replacement
-   -- sprites.
-   local player_rel_x, player_rel_y = player_pos_x+8, player_pos_y+8
 
    -- check the tile the player is standing on
-   if fget(mget(player_rel_x, player_rel_y), 1) then
-      return player_rel_x, player_rel_y
+   if fget(get_tile(player_x, player_y), 1) then
+      return player_x, player_y
    end
 
    -- check the tile the player is facing
    faced_tile_x, faced_tile_y = get_position_facing()
-   if fget(mget(faced_tile_x, faced_tile_y), 1) then
+   if fget(get_tile(faced_tile_x, faced_tile_y), 1) then
       return faced_tile_x, faced_tile_y
    end
 
    return nil, nil
 end
 
+-- NB: this function calls get_tile() and references the
+--     object_interaction_map from world.lua
 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 sprite = get_tile(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
+   -- modify the tile by writing the change to the mod_buffer
+   -- (the rendered image will be updated by draw_world()
    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
+   return player_x+facing_h, player_y+facing_v
 end
 
--- pos is camera position, meaning the map-relative player
--- position is pos + {8, 8}.
+-- NB: this function calls get_tile() from world.lua
 function legal_move(pos_x, pos_y)
-   return not fget(mget(pos_x+8, pos_y+8), 0)
+   return not fget(get_tile(pos_x, pos_y), 0)
 end
diff --git a/world.lua b/world.lua
index 00851ee..421489f 100644
--- a/world.lua
+++ b/world.lua
@@ -85,15 +85,15 @@ function init_world()
    -- 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
    -- coordinates. this is to flatten the buffer so that #mod_cache is useful
-   -- for checking against max_mod_entries.
-   max_mod_entries = 4096
+   -- for checking against the number of allowed entries
    mod_buffer = {}
+   mod_queue = {}
 end
 
 -- draw the sprites for this part of the world to the screen
 -- this calculates everything about the world fresh every frame,
 -- but pico-8 handles this just fine!
-function draw_world_segment(start_x, start_y)
+function draw_world(start_x, start_y)
    for x=0,15 do
       for y=0,15 do
          spr(get_tile(start_x-8+x, start_y-8+y), x*8, y*8)
@@ -172,16 +172,25 @@ function get_mod_key(x, 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
+function write_map_change(new_sprite, x, y, perm)
+   if #mod_buffer >= 8192 then
       cull_mod_buffer()
    end
+   local key = get_mod_key(x, y)
+   mod_buffer[key] = new_sprite
 
-   mod_buffer[get_mod_key(global_x, global_y)] = new_sprite
+   -- the queue gives us a time-ordered list of items to delete.
+   -- anything that should persist is simply not added to the queue,
+   -- making it un-deletable.
+   -- obviously if we end up with a *very large number* of persistent
+   -- objects we can run into trouble, but this is functionally a design
+   -- limitation.
+   if not perm then
+      add(mod_queue, key)
+   end
 end
 
 function cull_mod_buffer()
-   -- we cull 10% of the mod buffer at a time
-   -- todo: implement this
+   -- we cull 512 entries at a time.
+   -- stub: implement me!
 end