a_pleasant_stroll/movement.lua

function init_movement(start_pos)
   camera_pos = start_pos

   -- [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]}

   if btnp(0) or btnp(1) or btnp(2) or btnp(3) then
      if btnp(0) then
         new_pos[1] -= 1 -- move left
         facing[2] = -1
      end
      if btnp(1) then
         new_pos[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
         facing[1] = -1
      end
      if btnp(3) then
         new_pos[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
   end
   
   -- todo: determine whether we need to regen map and what that means
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 player position is
-- pos + {8, 8}.
function legal_move(pos)
   return not fget(mget(pos[1]+8, pos[2]+8), 0)
end