; TetrOS
; version 1.01 (05-09-2004)
; coded by Privalov

; For your playing pleasure, it's a boot-sector Tetris game.
; The quick help on keys:
;   Left - move left
;   Right - move right
;   Up - rotate
;   Down - drop
;   Esc - new game at any time
; Requires VGA and 386 or higher processor.

org 7c00h

ROWS = 23
DELAY = 20

virtual at 46Ch
  clock dw ?
end virtual

virtual at bp
  current dw ?
  current_column db ?
  current_row dw ?
  last_tick dw ?
  delay dw ?
  random dw ?
  score dw ?
end virtual

label well at 9000h
label pics at well-2*64

	cli
	xor	ax,ax
	mov	ss,ax
	mov	ds,ax
	mov	es,ax
	mov	sp,0FFFEh
	sti
	push	ax
	push	start
	retf

start:
	mov	al,13h
	int	10h
	mov	di,3*4
	mov	ax,int_3
	stosw
	xor	ax,ax
	stosw

	mov	bp,8000h

	mov	di,pics
	mov	cx,64
	inc	ax
	rep	stosb
	mov	ah,15
	mov	dx,7
      @@:
	mov	al,15
	stosb
	mov	al,ah
	mov	cl,6
	rep	stosb
	mov	al,8
	stosb
	mov	ah,7
	dec	dx
	jnz	@b
	mov	cl,8
	rep	stosb

	mov	ax,[clock]
	mov	[last_tick],ax
	mov	[random],ax
	mov	byte [current_row+1],well shr 8

	xor	ax,ax
	mov	[score],ax
	dec	ax
	stosw
	stosw
	stosw
	mov	cl,ROWS
    new_piece:
	mov	ax,1100000000000011b
	rep	stosw
      @@:
	mov	bx,[random]
	mov	ax,257
	mul	bx
	inc	ax
	mov	cx,43243
	div	cx
	mov	[random],dx
	and	bx,7
	cmp	bx,7
	je	@b
	shl	bx,1
	mov	ax,[pieces+bx]
	mov	[current],ax
	mov	word [current_column],6 + ((3+ROWS-4)*2) shl 8
	xor	ch,ch
	mov	ax,test_piece
	int3
	mov	al,draw_piece and 0FFh
	int3
	or	ch,ch
	jz	update_screen
	xor	bp,bp

process_key:
	xor	ah,ah
	int	16h
	mov	al,ah
	dec	al
	jz	start
	or	bp,bp
	jz	process_key
	mov	si,rotate
	cmp	al,48h-1
	je	action
	mov	si,left
	cmp	al,4Bh-1
	je	action
	mov	si,right
	cmp	al,4Dh-1
	je	action
	cmp	al,50h-1
	je	drop_down
	jmp	main_loop

action:
	call	do_move
	jmp	update_screen

drop_down:
	mov	si,down
	call	do_move
	jz	drop_down

update_screen:
	mov	bx,7
	mov	dx,12h
	mov	ah,2
	int	10h
	mov	cl,12
      @@:
	mov	ax,[score]
	shr	ax,cl
	and	al,0Fh
	cmp	al,10
	sbb	al,69h
	das
	mov	ah,0Eh
	int	10h
	sub	cl,4
	jnc	@b
	push	es 0A000h
	pop	es
	mov	si,well+3*2
	mov	di,320*184+112
      draw_well:
	lodsw
	push	si
	xchg	bx,ax
	shr	bx,2
	mov	dl,12
      draw_row:
	shr	bx,1
	salc
	and	ax,64
	mov	si,pics
	add	si,ax
	mov	al,8
      copy_line:
	mov	cx,8
	rep	movsb
	add	di,320-8
	dec	ax
	jnz	copy_line
	sub	di,320*8-8
	dec	dx
	jnz	draw_row
	sub	di,320*8+12*8
	pop	si
	cmp	si,well+(3+ROWS)*2
	jb	draw_well
	pop	es

main_loop:
	mov	ah,1
	int	16h
	jnz	process_key
	mov	ax,[clock]
	sub	ax,[last_tick]
	cmp	al,DELAY
	jb	main_loop
	add	[last_tick],ax
	mov	si,down
	call	do_move
	jz	update_screen
    lay_piece:
	mov	dx,1
	mov	si,well+3*2
	mov	di,si
	mov	cx,ROWS
      check_row:
	lodsw
	cmp	ax,1111111111111111b
	je	remove_row
	stosw
	dec	cx
	jmp	check_next_row
      remove_row:
	shl	dx,1
      check_next_row:
	cmp	si,well+(3+ROWS)*2
	jb	check_row
	add	[score],dx
	jmp	new_piece

do_move:
	mov	ax,clear_piece
	int3
	push	dword [current]
	call	si
	xor	ch,ch
	mov	al,test_piece and 0FFh
	int3
	mov	al,draw_piece and 0FFh
	pop	edx
	or	ch,ch
	jz	@f
	mov	dword [current],edx
      @@:
	int3
      no_move:
	ret
down:
	sub	byte [current_row],2
	ret
left:
	dec	[current_column]
	ret
right:
	inc	[current_column]
	ret
rotate:
	mov	cx,3
     @@:
	bt	[current],cx
	rcl	dx,1
	add	cl,4
	cmp	cl,16
	jb	@b
	sub	cl,17
	jnc	@b
	mov	[current],dx
	ret

int_3:
	mov	di,[current_row]
	mov	bx,4
      on_piece_row:
	mov	dx,[current]
	mov	cl,bh
	shr	dx,cl
	and	dx,1111b
	mov	cl,[current_column]
	add	cl,4
	shl	edx,cl
	shr	edx,4
	call	ax
	add	bh,4
	scasw
	dec	bl
	jnz	on_piece_row
	iret

clear_piece:
	not	dx
	and	[di],dx
	ret
test_piece:
	test	[di],dx
	jz	@f
	or	ch,1
      @@:
	ret
draw_piece:
	or	[di],dx
	ret

pieces dw 0010001000100010b
       dw 0010011000100000b
       dw 0010001001100000b
       dw 0100010001100000b
       dw 0000011001100000b
       dw 0100011000100000b
       dw 0010011001000000b

rb 7C00h+510-$
dw 0AA55h