;   _________  _______  ________  ______    __  _______
;  /__   ___/ / _____/ /__  ___/ / ____ \  / / / _____/
;     / /    / /____     / /    / /___/ / / / / /____
;    / /    / _____/    / /    / __   _/ / / /____  /
;   / /    / /____     / /    / /  \ \  / / _____/ /
;  /_/    /______/    /_/    /_/   /_/ /_/ /______/
;
;
;  256 byte tetris game by megasys
;  <megasys@intro.hu>
;
;  Released at Flag2oo2 party (Hungary)
;  http://flag2002.demoscene.hu
;
;  Missing features:
;  - game over check
;  - quick drop
;
;

[segment .text]
[bits 16]
[org 100h]

SCREEN_HEIGHT equ       20
STACK_WIDTH   equ       10
SHAPE_CHAR    equ       219                          ; 219 = filled block
SPEED         equ       20                           ; VGA VSYNC/down
VIDEO_MODE    equ       1
SCREEN_WIDTH  equ       40

;
; SS = DS = CS, de csak ha a Csink is ugy akarja
;

              push      word 0b800h
              pop       es                           ; ES <- video RAM

              mov       ax, VIDEO_MODE
              int       10h                          ; text mode (kivéve, ha valamelyik barom fent átírta)
newshape:
              xor       ax, ax
              mov       si, ax
              mov       di, word STACK_WIDTH - 2     ; kozepen
rndloop:
              in        al, 40h                      ; PIT counter = rnd :)
              cmp       al, 6                        ; nekunk 0..5 kell
              jnc       rndloop
              mov       bx, ax
              mov       al, byte [shapes + bx]
              mov       bp, ax
              shl       bp, 4                        ; BP-ben a shape
              add       al, 9
              mov       bh, al                       ; BH-ben a color
              mov       bl, SHAPE_CHAR

;
;  Jatekterulet falainak kirajzolasa, es a teli sorok eltuntetese
;

              pusha
              xor       di, di
sorok:
              mov       ax, 8*256 + SHAPE_CHAR
              stosw                                  ; es bal oldali fal lesz belole
              mov       cl, STACK_WIDTH
              mov       dl, cl
scan:
              scasw                                  ;
              jnc       nincs                        ;
              dec       dl                           ; van
nincs:
              loop      scan
              stosw                                  ; meg jobb oldali fal
              and       dl, dl                       ; tele van-e a sor?
              jnz       nincstele                    ; mert ha igen, akkor a folotte levoket egyel lejebb kell huzatni
              push      di                           ; scrollozzunk
              lea       si, [di - SCREEN_WIDTH * 2]
              std                                    ; visszafele megyunk
              mov       cx, si                       ; 0-ig
              rep       es movsb                     ; hajra
              cld
              pop       di
nincstele:
              lea       di, [di + (SCREEN_WIDTH - STACK_WIDTH  - 2) * 2]
              cmp       di, SCREEN_WIDTH * 2 * SCREEN_HEIGHT
              jc        sorok
              mov       cl, STACK_WIDTH + 2
              rep       stosw

              popa

;
;  Game loop
;

              mov       dx, 3dah
gameloop:
              mov       cx, SPEED
retrace:
              and       si, si
              jnz       newshape
retrace_in:
              in        al, dx
              and       al, 8
              jnz       retrace_in
noretrace:
              mov       ah, 1
              int       16h
              jz        nincsgomb
              xor       ah, ah
              int       16h
              cmp       al, 27
              jnz       noexit
              ret
noexit:
              sub       al, "j"
              cmp       al, 3
              jnc       nemjogomb
              dec       al
              shl       al, 1
              cbw                                    ; ezt az AX-et kell majd a DI-hez adni
mozgatas:
              push      ax                           ; letoroljuk a shape-t
              mov       ax, word SHAPE_CHAR
              call      drawshape
              pop       ax

              push      di                           ; eredeti pozicio
              push      bp                           ; es alakzat mentese
              add       di, ax                       ; muveletek: mozgatas
              and       ax, ax
              jnz       nemforgat

;
;
;  abcdefgh jklmnopq -> dhmqcglp bfkoaejn -> ndhmqcgl pbfkoaej
;
;


              push      cx                           ; muveletek: forgatas
              mov       cl, 16
              mov       ax, 1111h                    ; ez jelzi, hogy hol kell visszaforgatni 1-et...
forgatas:
              rol       bp, 4
              rcl       ax, 1
              jnc       forgatas2                    ; ...itt kell ;)
              ror       bp, 1
forgatas2:
              loop      forgatas
              ror       ax, 1
              mov       bp, ax
              pop       cx
nemforgat:
              xor       ax, ax                       ; collision check mode
              call      drawshape
              and       ah, 8
              jz        nocoll
              pop       bp                           ; eredeti alakzatok visszatoltese
              pop       di
              jmp       short nincsgomb
nocoll:
              xor       si, si
              pop       ax
              pop       ax
nincsgomb:
              mov       ax, bx
              call      drawshape
nemjogomb:

              in        al, dx
              and       al, 8
              jz        noretrace

              dec       cl
              cmp       cl, 1
              jnz       nemmegy
              mov       ax, SCREEN_WIDTH * 2
              inc       si
              jmp       short mozgatas
nemmegy:
              cmp       cl, 0
              jnz       retrace


              jmp       short gameloop


;
;  Shape kirajzolasa
;  IN:
;      BP = Shape
;      DI = Position
;      AX = Color + Character
;           AX = 0 -> collision check mode
;           AH = 0 -> fekete szin (gyk. erase mode), az AL-ben a karakter
;  OUT:
;    collision check mode:
;      AH = 0     -> no collision
;           other -> collision
;
;  REG DESTROY: NONE
;

drawshape:
              push      di
              push      cx

              mov       cl, 4
loop_row:
              push      cx
              mov       cl, 4
loop_col:
              rol       bp, 1
              jnc       nemrajzol
              and       al, al
              jz        draw_collisioncheck
              mov       [es:di], ax
draw_collisioncheck:
              or        ah, byte [es:di + 1]
nemrajzol:
              inc       di
              inc       di
              loop      loop_col
              pop       cx
              lea       di, [di + (SCREEN_WIDTH - 4) * 2]
              loop      loop_row

              pop       cx
              pop       di
              ret

; middle two rows (of 4)

shapes        db        01110100b       ; 0 = L
              db        01110001b       ; 1 = J
              db        00110110b       ; 2 = s
              db        01100011b       ; 3 = z
              db        01110000b       ; 4 = I
              db        01110010b       ; 5 = T