VGA image on dos without borders.

Last Updated or created 2022-07-06

This year i’ve been really into assembly on Intel x86 machines.
With EDK we made some demo’s and generally trying to find the limits of the machines we had.

Funny story, edk made a program which changed the palette every scanline (if memory serves me right), while running the program and looking at the screen the colors faded to grayscale. (Something with run-away tables) We look at eachother and said: We must have been using up all colors, we need to refill the graphics card.

I previously made a copperbar alike thingy on a hercules system. (Have not seen them before on a pc back then )
But with below program, i could display pictures which removed the borders.

Below a nsfw video example (pass protected), but a simplified example in pictures below that.

Restricted Content
To view this protected content, enter the password below:

    name split_screen
.286

parm_vert equ 0

data segment
intmsk      db ?
oldvidtab   db 18h dup (?)      ;actuele video-parameters
newvidtab   label byte
            ;HORIZONTAAL
            db 0
            db 12
            db 12
            db 0
            ;VERTIKAAL
            db 0
            db 5
            db 5
            db 0;-40
            ;
            db 0
            db 0
            db 0
            db 0
            db 0
            db 0
            db 0
            db 0
            db 0
            db 0
            db 0
            ;       REGISTER 13H (OFFSET)
            db 0
            ;
            db 18h dup (0)
data ends

stack segment stack
    dw 128 dup (?)
stack ends

code    segment
        assume cs:code,ds:data
cols label byte
set_scrparms:
    mov dx,3d4h
    mov al,11h
    out dx,al
    inc dx
    in al,dx
    and al,7fh  ;clear bit 7: enable writes to vga reg 0..7
    out dx,al
    dec dx
    mov al,13h      ;offset register
    out dx,al
    inc dx
    in al,dx        ;get actual value
    add al,4
    out dx,al
    ret
;
; RE-INIT DISPLAY ROUTINE
;
get_oldvidparms:
    mov dx,3d4h
    mov cx,18h  ;18h registers
    mov di,offset oldvidtab
    mov bl,0    ;begin met register 0
govp1:
    mov al,bl   ;register index
    out dx,al
    inc dx      ;3d5
    in al,dx    ;get actual register content
    dec dx
    mov [di],al
    inc di
    inc bl      ;volgend register
    loop govp1

    mov si,offset oldvidtab
    mov di,offset newvidtab
    mov cx,18h
donewparms:
    mov al,[si]
    add al,[di]
    mov [di],al
    inc si
    inc di
    loop donewparms
    ret
set_newvidparms:
    mov dx,3d4h
    mov cx,18h  ;18h registers
    mov si,offset newvidtab
    mov bl,0    ;begin met register 0
snvp1:
    mov al,bl   ;register index
    out dx,al
    inc dx      ;3d5
    mov al,[si]
    inc si
    out dx,al   ;set register value
    dec dx
    inc bl      ;volgend register
    loop snvp1
    ret

;
; MAIN ENTRY POINT
;
init:
    mov ax,data
    mov ds,ax
    in al,21h
    mov intmsk,al
    cli
    mov al,11111101b
    out 21h,al
    sti
    mov ax,13h
    int 10h
;extend video-memory to 256kb or more
    mov dx,3ceh
    mov al,06h
    out dx,al
    inc dx
    in al,dx
    and al,0f3h
    out dx,al
    ;
    mov ax,0a000h
    mov es,ax
    call set_scrparms
    call get_oldvidparms
    call set_newvidparms
    mov dx,3cch
    in al,dx
    and al,03fh
    mov ah,parm_vert
    ror ah,2
    or al,ah
    mov dx,3c2h
    out dx,al
;
    ;
    push ds
    mov ax,5000h
    mov ds,ax
;
; pallet
;

setpal:
    mov dx,3c8h
    xor al,al
    out dx,al
    inc dx
    mov cx,256*3
    mov si,100h
    cld
    rep outsb
;disp picture routine
    mov ax,6000h
    mov ds,ax
    mov si,0
    mov di,0
    mov ax,0
    mov cx,352*8
    cld
    rep stosw
    mov si,di
    mov cx,8
    cld
    rep stosw
    mov bp,170
    mov si,di
 hiero:
    mov cx,320
    cld
    rep movsb
    mov ax,0
    mov cx,16
    cld
    rep stosw
    mov si,di
    dec bp
    jnz hiero


    xor si,si
    xor di,di
    mov ax,0b000h
    mov es,ax
    mov ax,07000h
    mov ds,ax
    mov cx,3000
    cld
    mov ax,0
    rep stosw
    mov ax,0a000h
    mov es,ax

    mov ax,6000h
    mov ds,ax
    mov di,0
    mov si,di
rhiero:
    push ax
    mov ah,8
    int 21h
    pop ax
    std
    mov cx,-1
    rep movsb


    xor si,si
    xor di,di
    mov ax,0b000h
    mov es,ax
    mov ax,07000h
    mov ds,ax
    mov cx,3000
    cld
    rep movsw
    mov ax,0a000h
    mov es,ax
    pop ds
    ;
mloop:
    mov dx,3dah
wtv1:
    in al,dx
    test al,8
    jnz wtv1
wtv2:
    in al,dx
    test al,8
    jz  wtv2
    mov ah,1
    int 16h
    jz mloop
    xor ah,ah
    int 16h
exit:
    mov ax,3
    int 10h
    cli
    mov al,intmsk
    out 21h,al
    sti
    mov ax,4c00h
    int 21h

code ends
end init