pico-8 cartridge // http://www.pico-8.com
version 35
__lua__
-- snake game
-- copyright @eyuzwa
-- released under
-- mit license
--
-- note:
-- this source is split into
-- different tabs in the
-- pico8 editor
-- tab0: _init
-- tab1: _draw
-- tab2: _update


-- version
version="0.4"

-- global variables
x={}
y={}
x_dir=0
y_dir=0
score=0

-- we are splitting up our 
-- screen into tiles
-- the larger the tile_num,
-- the larger the game area
tile_num=32
tile_size=128/tile_num

-- track our fruit position
-- and color
fruit={}
fruit.x=0
fruit.y=0
fruit.color=8

-- startup function called
-- by pico8
-- used to initialize and
-- setup our game
function _init()

 -- generate snake head
 -- starting position
 -- todo: randomize it?
 x[1]=tile_size*(tile_num/4)
 y[1]=tile_size*(tile_num/2)

 -- start off moving right
 x_dir=1
 
 -- set starting snake tail
 -- length
 for i=2,7 do
  x[i]=((x[i-1]/tile_size)-1)*tile_size
  y[i]=y[1]
 end
 
 -- generate fruit
 update_fruit()
end

-->8
-- main draw method called
-- by pico8
-- clear the screen and draw
-- everything
function _draw()
 cls(1)
 draw_snake()
 draw_fruit()
 draw_score()
 
 -- draw version
 print("v"..version,100,1)
end

-- draw fruit
function draw_fruit()
 rectfill(fruit.x,fruit.y,fruit.x+tile_size-1,fruit.y+tile_size-1,fruit.color)
end

-- draw score
function draw_score()
 color(10)
 print("score: "..score,1,1)
end

-- draw snake
function draw_snake()
 -- draw snake head
 rectfill(x[1],y[1],x[1]+tile_size-1,y[1]+tile_size-1,10)
  
 -- draw snake segments
 for i=2,#x do
  rectfill(x[i],y[i],x[i]+tile_size-1,y[i]+tile_size-1,3)
 end
  
end

-->8
-- main update function
-- called by pico8
-- updated at 30fps
-- todo: look at _update60
function _update()

 -- check for wall collision
 if(is_wall_collision()) then
  return
 end

 -- capture input
 update_input()
 
 -- check for collision
 -- with fruit
 local collide=false
 collide=is_fruit_collision()
 if(collide)then
  -- increment score
  score=score+10
  
  -- push new snake segment
  -- using the position of
  -- the fruit
  for i=#x+1,2,-1 do
   x[i]=x[i-1]
   y[i]=y[i-1]
  end
  
  x[1]=fruit.x
  y[1]=fruit.y
  
  -- generate a new fruit
  update_fruit()
 else
  update_snake()
 end
end

-- generate a random (x,y)
-- to place the fruit
function update_fruit()
 fruit.x=flr(rnd(tile_num))*tile_size
 fruit.y=flr(rnd(tile_num))*tile_size 
end


function update_input()
 --btn(0) left
 --btn(1) right
 --btn(2) up
 --btn(3) down
 
 if(btn(0)) then
  x_dir=-1
  y_dir=0
 elseif(btn(1)) then
  x_dir=1
  y_dir=0
 elseif(btn(2)) then
  x_dir=0
  y_dir=-1
 elseif(btn(3)) then
  x_dir=0
  y_dir=1
 end
end


function update_snake()
 
 -- local temp variables
 local temp1x = x[1]
 local temp1y = y[1]
 local temp2x, temp2y
 
 -- update snake head segment
 x[1] += (x_dir * tile_size)
 y[1] += (y_dir * tile_size)
 
 -- update snake tail segments
 for i=2,#x do
  temp2x=x[i]
  temp2y=y[i]
  
  x[i]=temp1x
  y[i]=temp1y
  
  temp1x=temp2x
  temp1y=temp2y
 end
 
end


function is_fruit_collision()
 if(x[1]+(x_dir*tile_size) == fruit.x and y[1]+(y_dir*tile_size) == fruit.y) then
   return true
 end
 return false
end

function is_wall_collision()
 if(x[1] > 128 or x[1] < 0 or y[1] < 0 or y[1] > 128) then
  return true
 end
 return false
end

__gfx__
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