Xorun

run this game using Gforth, like this

gforth xorun.fs

or you can just paste the code into Gforth's REPL.

---

this game is a submission to TweetTweetJam 9. here is the code

require random.fs
: v variable ;
v y
v f
v b
v d
create s 256 allot
: dd 32 * + s + c! ;
7 y !
0 f !
utime b ! seed !
12 d !
: . 0 begin
s 256 bl fill page
f @ if -1 f +! -1 y +! else y @ 7 < if 1 y +! else
key? if key drop 5 f ! then
b @ 1 and if exit then
then then
d @ random 0= if b @ 32768 or b ! then
b @ 32 0 do dup 1 and if 88 i 7 dd then 2/ loop drop
b @ 2/ b !
79 0 y @ dd
1+ dup 255 mod 0= d @ 4 > and if -1 d +! then
dup .
s 8 0 do dup 32 type cr 32 + loop drop
83 ms .s
again ;
. bye

meanings of the variables

- s - screen, a 32*8 area of bytes. a char is assumed to be one address unit.

- y - y coordinate.

- f - time to fly. increase y when f positive.

- b - blocks. a number whose lower 32 bits represent obstacles

- d - density. pick a number in [0, d). if it's zero, place a new block.

- unnamed stack item - your score. it stays on the stack after the game ends.