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_[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()  # 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()
   player_x, player_y = 0, 0

   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_x, new_y = player_x, player_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_x -= 1 -- move left
         facing_h = 0xffff
      end
      if btnp"1" then
         new_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_y -= 1 -- move up
         facing_v = 0xffff
      end
      if btnp"3" then
         new_y += 1 -- move down
         facing_v = 1
      end
      if not (btnp"2" or btnp"3") then
         facing_v = 0
      end
   end

   -- 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

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

-- 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.

   -- check the tile the player is standing on
   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(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 = get_tile(x, y)
   local data = object_interaction_map[sprite]
   -- todo: figure out playing sound effects, animation?

   -- 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 player_x+facing_h, player_y+facing_v
end

-- NB: this function calls get_tile() from world.lua
function legal_move(pos_x, pos_y)
   return not fget(get_tile(pos_x, pos_y), 0)
end