snake.p8

pico-8 cartridge // http://www.pico-8.com
version 42
__lua__
// a simple snake game
// inspired by coding trains
// code challenge 3 - snake
// https://www.youtube.com/watch?v=aagk-fj-bam
width = 128
height = 128
swidth = 2
fwidth = 2
endgame = false
speed = 1

function create_snake()
  snake = {}
  -- ensure the snake doesn't
  -- spawn too close to the
  -- edge of the screen
  snake.x = flr(rnd(width/2)) 
    + 32
  snake.y = flr(rnd(height/2)) 
    + 32
  snake.xspeed = 1
  snake.yspeed = 0
  snake.total = 0
  snake.tail = {}
  return snake
end

function reset_food()
  f = {}
  -- -4 and +8 are here to stop
  -- food spawning in the border
  f.x = flr(rnd(width-4)) + 2
  f.y = flr(rnd(height-4)) + 2
  return f
end

function init_game() 
  snake = create_snake()
  food = reset_food()
  endgame = false
end

init_game()

function change_direction()
  if btn(0) then
    snake.xspeed = -speed
    snake.yspeed = 0
  elseif btn(1) then
    snake.xspeed = speed
    snake.yspeed = 0
  elseif btn(2) then
    snake.xspeed = 0
    snake.yspeed = -speed
  elseif btn(3) then
    snake.xspeed = 0
    snake.yspeed = speed
  end
end

function move_snake()
  -- rotate the tail by shifting  
  -- the tail to leave an empty
  -- slot for the current x/y
  -- drops the oldest tail pixel
  for i=1,count(snake.tail)-1 do
    snake.tail[i] 
      = snake.tail[i + 1] 
  end
  -- add the current snake pos
  -- to the tail
  if snake.total >= 1 then
    new_tail = {}
    new_tail.x = snake.x
    new_tail.y = snake.y
  
    snake.tail[snake.total] 
      = new_tail
    printh(count(snake.tail))
  end
 
  -- move the snake
  snake.x += snake.xspeed
  snake.y += snake.yspeed
end

function check_endgame()
  snake_out_of_bounds = (
    snake.x < 1
    or snake.x > width - 2
    or snake.y < 1
    or snake.y > height - 2
  )

  snake_ate_itself = false
  for i=1,count(snake.tail) do
    tail_bit = snake.tail[i]
    snake_ate_itself = (
      snake.x == tail_bit.x 
      and snake.y == tail_bit.y
    )
    if snake_ate_itself then
      break
    end
  end
   
  endgame = snake_out_of_bounds
    or snake_ate_itself
end

function eat()
  eat_x_diff = abs(
    snake.x - food.x
  )
  eat_y_diff = abs(
    snake.y - food.y
  )
  if (
    (snake.x == food.x 
     and eat_y_diff < 4)
    or
    (snake.y == food.y
     and eat_x_diff < 4
    )
  ) then
    food = reset_food()
    snake.total += 1
  end
end

function _update()
  if not endgame then
    change_direction()
    move_snake()
    check_endgame()
    eat()
  else 
    if btnp(4) then
      init_game()
    end 
  end
end

function cprint(text, y, c)
    local x = (128 - (#text * 4)) / 2
    print(text, x, y, c)
end

function _draw()
  cls()
  
  -- score is just the number
  -- of food eaten
  print("score: ", 2, 2)
  print(snake.total)
	   
  -- draw the game b0undary
  rect(
    0, 0, width-1, height-1, 7
  )

  -- draw the food  
  circfill(
    food.x, food.y, fwidth, 3
  )
  -- and the snake
  circfill(
    snake.x, snake.y, swidth, 7
  )
  -- and it's tail
  for i=1,count(snake.tail) do
    tail = snake.tail[i]
    circfill(
      tail.x, tail.y, 1, 7
    )
  end
  
  if endgame then
    print("game over", 30, height/3)
    print(
      "press `o` to play again"
    )
  end
end