Implement infinite scrolling.

player.lua

@@ -0,0 +1,106 @@
+-- this module assumes all objects and the player are
+-- 1x1 sprite in size. larger sprites are not currently supported
+--
+-- exported variables:
+--   player_pos # integer tuple {x,y}. absolute position of the player on the
+--              #   'world map'
+--   camera_pos # integer tuple {x,y}. Represents top-left position of the
+--              #   pico-8 camera on the pico-8 map
+--   facing     # integer tuple {v,h}. Current facing of the player. Values of
+--              #   each element can be -1 (up or left), 0 (neutral),
+--              #   or 1 (down or right)
+--
+-- exported constants:
+--   player_lookup # used internally to look up the sprite to render for a
+--                 #   given facing
+--
+-- 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.
+
+function init_player(start_pos)
+   -- camera_pos is the relative coordinate of the camera
+   -- on the currently generated map chunk. player_pos is
+   -- the *absolute* world coordinates of the player.
+   player_pos = start_pos
+   camera_pos = {start_pos[1]-8, start_pos[2]-8}
+
+   -- [1] is vertical facing, [2] is horizontal, -1 is up/left, 0 is neutral,
+   -- and 1 is down/right
+   facing = {1, 0}
+
+   -- this is a constant for looking up player sprites by facing
+   player_lookup = {
+      [0] = {
+         [0] = -1, -- error state
+         [-1] = 122, -- left
+         [1] = 123, -- right
+      },
+      [-1] = {
+         [0] = 120, -- up
+         [-1] = 124, -- up-left
+         [1] = 125, -- up-right
+      },
+      [1] = {
+         [0] = 121, -- down
+         [-1] = 126, -- down-left
+         [1] = 127, -- down-right
+      },
+   }
+end
+
+
+function handle_input()
+   local new_pos = {camera_pos[1], camera_pos[2]}
+   local new_ppos = {player_pos[1], player_pos[2]}
+
+   if btnp(0) or btnp(1) or btnp(2) or btnp(3) then
+      if btnp(0) then
+         new_pos[1] -= 1 -- move left
+         new_ppos[1] -= 1
+         facing[2] = -1
+      end
+      if btnp(1) then
+         new_pos[1] += 1 -- move right
+         new_ppos[1] += 1 -- move right
+         facing[2] = 1
+      end
+      if not (btnp(0) or btnp(1)) then
+         facing[2] = 0
+      end
+
+      if btnp(2) then
+         new_pos[2] -= 1 -- move up
+         new_ppos[2] -= 1 -- move up
+         facing[1] = -1
+      end
+      if btnp(3) then
+         new_pos[2] += 1 -- move down
+         new_ppos[2] += 1 -- move down
+         facing[1] = 1
+      end
+      if not (btnp(2) or btnp(3)) then
+         facing[1] = 0
+      end
+   end
+
+   if _legal_move(new_pos) then
+      camera_pos = new_pos
+      player_pos = new_ppos
+   end
+end
+
+function draw_player()
+   spr(player_lookup[facing[1]][facing[2]], 64, 64)
+   -- todo: animate the character on move
+end
+
+-- pos is camera position, meaning the map-relative player
+-- position is pos + {8, 8}.
+function _legal_move(pos)
+   return not fget(mget(pos[1]+8, pos[2]+8), 0)
+end