Write character on vga mode

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Arturx87

Joined: 16 Mar 2023
Posts: 1

Arturx87 16 Mar 2023, 07:44

How to draw character in vga mode (13h) in my select position (example 2px x 4px)

Code:

Mov al,’a’
Mov ah,0eh
Int10h

Thanks for Help

16 Mar 2023, 07:44

macomics

Joined: 26 Jan 2021
Posts: 819
Location: Russia

macomics 16 Mar 2023, 09:17

If I remember correctly, there is no function for drawing text in an arbitrary position for VGA mode. But if you just need to output the text, then you can use the function AH=13h.

Code:

push es
push cs
pop es
mov ax, 1300h ; al = mode
mov bx, 0007h ; bh = page, bl = color
mov cx, text0.Length ; ...
mov dx, 0402h ; dh = row, dl = column
mov bp, text0 ; es:bp = string
int 10h
pop es

push es
push cs
pop es
mov ax, 1301h ; al = mode
mov bx, 0007h ; bh = page, bl = color
mov cx, text1.Length ; ...
mov dx, 0607h ; dh = row, dl = column
mov bp, text1 ; es:bp = string
int 10h
pop es

push es
push cs
pop es
mov ax, 1302h ; al = mode
mov bh, 00h ; bh = page
mov cx, text2.Length ; ...
mov dx, 0802h ; dh = row, dl = column
mov bp, text2 ; es:bp = string
int 10h
pop es

push es
push cs
pop es
mov ax, 1303h ; al = mode
mov bh, 00h ; bh = page
mov cx, text3.Length ; ...
mov dx, 0A04h ; dh = row, dl = column
mov bp, text3 ; es:bp = string
int 10h
pop es

text0 db 'Hello'
.Length = $ - text0
text1 db 'world'
.Length = $ - text1
text2 db 'H', 01h, 'e', 02h, 'l', 03h, 'l', 04h, 'o', 05h
.Length = ($ - text2) shr 1
text3 db 'w', 10h, 'o', 20h, 'r', 30h, 'l', 40h, 'd', 50h
.Length = ($ - text3) shr 1

But if you need to output the text in a completely arbitrary position, then you should use the function AH=1130h. You get a pointer to the character generator table, use it to decipher the character and output it by points with the function AH=0Ch or by direct access to video memory.

16 Mar 2023, 09:17

edfed

Joined: 20 Feb 2006
Posts: 4324
Location: Now

edfed 17 Mar 2023, 15:52

Code:

print:
.char:
        pushad
        movzx esi,al
        shl esi,3
        add esi,bioschars
        mov edi,.base
        mov eax,[edi+.x]
        mov ebx,[edi+.y]
        mov ch,8
.loadline:
        mov dh,[esi]
        mov dl,80h
.nextdot:
        test dh,dl
        je @f
        mov cl,[edi+.c];31
        call put.pixel
@@:
        inc eax
        shr dl,1
        jne .nextdot
        inc ebx
        mov eax,[edi+.x]
        inc esi
        dec ch
        jne .loadline
        add dword[edi+.x],8
        popad
        ret

.string:
;esi asciiz string
@@:
        lodsb
        or al,al
        je @f
        call .char
        jmp @b
@@:
        ret


.base = 10200h
.x    = 0
.y    = 4
.c    = 8

bioschars = 0ffa6eh
.xl=16
.yl=16

char table is at 0ffa6eh

putpixel is just like that:

Code:

.pixel:
        push ebx
        cmp eax,screen.xl
        jae @f
        cmp ebx,screen.yl
        jae @f
        imul ebx,screen.xl
        mov [screen.base+eax+ebx],cl
;        xor [screen.base+eax+ebx],cl
@@:
        pop ebx
        ret

and screen.base can be the double buffer, or direct to vram, as you want.

for CGA mode, it starts at 0a0000h

this code is intended for protected mode but just whows how to print chars.

17 Mar 2023, 15:52

DimonSoft

Joined: 03 Mar 2010
Posts: 1228
Location: Belarus

DimonSoft 17 Mar 2023, 20:17

There used to be functions that set/retrieve the current cursor position. Then one has to just add 1 plus 1.

17 Mar 2023, 20:17

macomics

Joined: 26 Jan 2021
Posts: 819
Location: Russia

macomics 17 Mar 2023, 20:43

edfed wrote:

char table is at 0ffa6eh

Only the first 128 characters.

To get pointers to the sign generator tables , there is a function AH=0x1130

DimonSoft wrote:

There used to be functions that set/retrieve the current cursor position. Then one has to just add 1 plus 1.

But not in graphical mode. The cursor works, of course, but you need to draw it yourself, but the coordinates continue to be tracked quite well. Although they work in text columns and rows, not in pixels.

17 Mar 2023, 20:43

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