Snake game for the TI-86 graphing calculator

snake.asm

; Snake 86 by David Phillips <david@acz.org>
; for the TI-86 graphing calculator
; written on January 28, 2000

#include "ti86asm.inc"

VideoRam    = $fc00
SnakeBody   = $9000

.org _asm_exec_ram

 nop
 jp Start
 .dw 0
 .dw Title

Start:
 call _runindicoff
 call _flushallmenus
 call _clrLCD

 sub a
 ld (_asapvar+1),a

 ld hl,VideoRam+128
 push hl
 ld de,VideoRam+129
 ld bc,31
 ld (hl),%11111111
 ldir
 inc hl
 ld (hl),%11000000
 ld l,160+15
 ld (hl),%00000011
 inc hl
 ex de,hl
 ld bc,51*16
 ldir
 pop hl
 ld c,32
 ldir

 ld hl,0
 ld (_curRow),hl
 ld hl,Title
 call _puts 

 call NewDot

Play:
 call _get_key
 cp K_EXIT
 jp z,_clrWindow
 dec a
 cp 4
 jr nc,SkipKeys
 ld (_@Direction),a 
SkipKeys:
 ld de,_@Head
 ld bc,2
_@Direction =$-2
 ld hl,DirTable
 add hl,bc
 add hl,bc
 ld a,(de)
 add a,(hl)
 ld (de),a
 inc hl
 inc de
 ld a,(de)
 add a,(hl)
 ld (de),a

 ld hl,_@Grow
 dec (hl)
 jr nz,GrowSnake
 inc (hl)
 ld hl,SnakeBody
_@Tail =$-2
 ld c,(hl)
 inc hl
 ld b,(hl)
 inc hl
 res 4,h
 ld (_@Tail),hl
 call NukePixel
GrowSnake:
 
 ld bc,(16<<8)+16
_@Head =$-2
 ld hl,SnakeBody
_@HeadTop =$-2
 ld (hl),c
 inc hl
 ld (hl),b
 inc hl
 res 4,h
 ld (_@HeadTop),hl
 push bc
 ld hl,0
_@Dot =$-2
 or a
 sbc hl,bc  
 call z,DoNewDot
 pop bc
 call CheckPixel
 jr nz,Crash
 call PutPixel

 ld b,10
Delay:
 halt
 djnz Delay
 jr Play

DoNewDot:
 call NukePixel
NewDot:
 call Random
 and %01111110
 cp 124
 jr nc,NewDot
 add a,2
 ld b,a
 call Random
 and %00111110
 cp 52
 jr nc,NewDot
 add a,10
 ld c,a
 ld (_@Dot),bc
 call PutPixel 
 ld a,1
_@Grow =$-1
 add a,5
 ld (_@Grow),a
 ld a,-1
_@Score =$-1
 inc a
 ld (_@Score),a
 ld h,0
 ld l,a

DispA:
 ld de,_OP1+5
 sub a
 ld (de),a
Unpack:
 dec de
 call _divHLby10
 add a,'0'
 ld (de),a
 ld a,h
 or l
 jr nz,Unpack
 ld hl,16<<8
 ld (_curRow),hl
 ex de,hl
 jp _puts 

Crash:
 ld hl,(8<<8)+3
 ld (_curRow),hl
 ld hl,GameOver
 call _puts
Wait:
 call _get_key
 or a
 jr nz,Wait
 jp _clrWindow

Random:
 ld a,r
 ld hl,_@Seed
_@Seed =$+1
 add a,0
 ld (hl),a
 ret

CheckPixel:
 call FindPixel
 and (hl)
 ret nz
 ld de,16
 add hl,de
 and (hl)
 ret

PutPixel:
 call FindPixel
 push af
 or (hl)
 ld (hl),a
 ld de,16
 add hl,de
 pop af
 or (hl) 
 ld (hl),a
 ret

NukePixel:
 call FindPixel
 cpl
 push af
 and (hl)
 ld (hl),a
 ld de,16
 add hl,de
 pop af
 and (hl)
 ld (hl),a
 ret

FindPixel:
 ld a,c
 add a,a
 add a,a
 ld l,a
 ld h,0
 add hl,hl
 add hl,hl
 ld a,b
 and %11111000
 rra
 rra
 rra
 add a,l
 ld l,a
 ld a,b
 rra
 and %00000011
 push hl
 ld d,0
 ld e,a
 ld hl,PixelMasks
 add hl,de
 ld a,(hl)
 pop hl
 ld de,VideoRam
 add hl,de
 ret 

PixelMasks:
 .db %11000000, %00110000, %00001100, %00000011

DirTable:
 .db 2,0, 0,-2, 0,2, -2,0

Title:
 .db "Snake 86",0

GameOver:
 .db "Game Over",0