a_pleasant_stroll/player.lua

-- This module assumes all objects and the player are 1x1 sprite in size.
-- 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)
--
-- 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_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

   facing_v = 1
   facing_h = 0

   -- this is a constant for looking up player sprites by facing
   player_lookup = {
      [0] = {
         [0] = 0xffff, -- error state
         [0xffff] = 122, -- left
         [1] = 123, -- right
      },
      [0xffff] = {
         [0] = 120, -- up
         [0xffff] = 124, -- up-left
         [1] = 125, -- up-right
      },
      [1] = {
         [0] = 121, -- down
         [0xffff] = 126, -- down-left
         [1] = 127, -- down-right
      },
   }
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

   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
         new_ppos_x -= 1
         facing_h = 0xffff
      end
      if btnp"1" then
         new_pos_x += 1 -- move right
         new_ppos_x += 1 -- move right
         facing_h = 1
      end
      if not (btnp"0" or btnp"1") then
         facing_h = 0
      end

      if btnp"2" then
         new_pos_y -= 1 -- move up
         new_ppos_y -= 1 -- move up
         facing_v = 0xffff
      end
      if btnp"3" then
         new_pos_y += 1 -- move down
         new_ppos_y += 1 -- move down
         facing_v = 1
      end
      if not (btnp"2" or btnp"3") then
         facing_v = 0
      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
   end
end

function draw_player()
   spr(player_lookup[facing_v][facing_h], 64, 64)
   -- todo: animate the character on move

   -- draw the player's HUD
   local interact_x, interact_y = can_interact()
   if interact_x and interact_y then
      spr(119, 0, 120)
   end

   -- 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
-- nil,nil if nothing to interact with
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
   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
      return faced_tile_x, faced_tile_y
   end

   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
end

-- pos is camera position, meaning the map-relative player
-- position is pos + {8, 8}.
function legal_move(pos_x, pos_y)
   return not fget(mget(pos_x+8, pos_y+8), 0)
end