Real Mode VGA Text?

pcmattman · Post by **pcmattman** » Wed Jan 31, 2007 3:20 pm

I've writing the graphical side of my OS but I've run into a problem... All the tutorials say that to print text I have to write to the framebuffer at 0xB800. Problem is, this does not work at all. No characters are printed. Any ideas?

Update: it works when I put the framebuffer code into the text-based side of my OS. how can I output text in 320x200 Mode 13?

Otter · Post by **Otter** » Wed Jan 31, 2007 3:49 pm

In vga mode 13h the frame buffer at segment 0xB800 should not work, but as you're in real mode you could use bios interrupts ( this does not look very good 'cause the letters are very big ) ... You could also write your own graphical routines to draw some letters

XCHG · Post by **XCHG** » Thu Feb 01, 2007 12:18 am

In Graphics Mode, you are working with pixels rather than characters therefore, you can create fonts yourself and then use them. Remember that the segment address of the Video Memory for Graphics Mode 320.200 is located at 0xA000 and not 0xB800. You can for example initialize the Graphics Mode of 320.200 and then use this segment address to write to the Video Memory.

Remember that in Text Mode of 80.25 with the Video Memory Segment located at 0xB800, you have one character followed by its attribute, therefore, you have 160 bytes in one row (80 characters + 80 attributes) and 25 row in total, making it 160*25=4000 bytes long.

In Graphics Mode of 320.200, you have one pixel which can be chosen among 256 different colors (0x00 - 0xFF) rather than a character with an attribute, therefore, you have 320 * 200 = 64000 pixels in total. If you start from 0xA000, you should end 0xA000:[0xFA00] which would be your last pixel.

I hope it would help.

pcmattman · Post by **pcmattman** » Thu Feb 01, 2007 12:21 am

Otter wrote:You could also write your own graphical routines to draw some letters

Any code you could refer me to?

XCHG · Post by **XCHG** » Thu Feb 01, 2007 12:40 am

This wasn't a reply to my post but anyway. Download the below ZIP file and it includes a file written in Borland Pascal. The ZIP file includes an executable file called "Fonts.exe" which takes advantage of fonts in 300.200 Graphics Mode.

If you run into troubles understanding the code, post back and I'll explain.

P.S: The code is not written by me and I am taking no credits neither responsibilities for it.

pcmattman · Post by **pcmattman** » Thu Feb 01, 2007 12:45 am

Um... download? Where?

XCHG · Post by **XCHG** » Thu Feb 01, 2007 12:48 am

Are you kidding me? right there ^^. At the bottom of my previous post. Anyway, here is the direct link.

pcmattman · Post by **pcmattman** » Thu Feb 01, 2007 12:49 am

lol it wasn't there 5 minutes ago

pcmattman · Post by **pcmattman** » Thu Feb 01, 2007 5:08 am

You wouldn't happen to know how to do that in NASM Assembly, or know of anywhere I could find some form of reference to do so myself?

Otter · Post by **Otter** » Thu Feb 01, 2007 5:24 am

The code does not really help because that what you want ( to load a font / to draw a letter ) is not included in the source ... I have no code for you but it should be not so hard, only a lot of work.

At first you need to create ( or convert ) a font. You should really use bitmap fonts at first, that means you create a little image for each letter. The easiest way is when you say that all letters are the same size. You could create a large image where all your letter-images are in.

If your kernel is able to handle devices and file systems you can simply load this font, otherwise you could link it directly to your graphical code.

[edit]Of course it's a lot of work to do this by hand. You should write a program to do so. It could use any systemfonts. If you know pascal and if you have BP7 you can use the fonts given by the attachment of XCHG: Simple change the demo program to draw a table of all letters, make a screenshot.[/edit]

XCHG · Post by **XCHG** » Thu Feb 01, 2007 6:41 am

Just to add a little to [Otter]'s post which should be enough for you to make a headway; I really don't know the structure of your OS and what mode you are working in. I could write an example for you if you wanted but I need to know whether you are working in PM or RM. Information about your GDT/IDT if in PM and etc. Let me know about these and I'll write an example code for you.

Dex · Post by **Dex** » Thu Feb 01, 2007 10:32 am

If you have vesa, than this may help:

Code: Select all

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;                                           ;;
;; fasm example.By Craig Bamford (Dex) 2002. ;;
;; 640*480 8bpp (256 colors) vesa1           ;;
;; C:\fasm vesa1.asm vesa1.com               ;;
;;                                           ;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
ORG    100h

Start:
        mov ax,4f02h
        mov bx,101h
        int 10h

        mov dx,0xa000
        mov es,dx
        call window

StartAgain:
        xor dx,dx
MainLoop:
        push dx
        call window
        xor bx,bx
        mov al,0x00
        call static
        call PutTextB
        call PutTextS
        pop dx
        cmp dx,4
        je StartAgain
        inc dx
        mov ah,00h
        int 16h
        jz MainLoop
        mov ax,0003h
        int 10h
        ret

window:
        mov ax,4f05h    
        mov bx,0
        int 10h
        xor bx,bx
        ret

static:
        stosb
        inc bx
        cmp bx,0x00000
        jne static
        ret

PutTopBackGround:
        xor di,di
        mov cx,0x1900
        mov al,0x81
        rep stosb
        ret
                     
PutBottomBackGround:
        mov di,58240
        mov cx,0x17c0
        mov al,0x81
        rep stosb
        ret

DrawImage:
        mov di,bx
        mov dl,[Row]
        cld
GetData:     
        lodsw
        mov bx,ax
        mov cl,16
CheckBit:
        test bx,0x8000
        jz ZeroBit
        mov al,dh    
        stosb
        jmp Skip                    
ZeroBit:
        inc di
Skip:
        shl bx,1
        loop CheckBit          
        add di,624
        dec dl
        jnz  GetData
        ret

PutTextB:
        mov byte [Row],16
        xor di,di
        mov di,716
        mov bx,di
        mov SI,TextS
        mov dh,0x0a
        call DrawImage

        xor di,di
        mov di,733
        mov bx,di
        mov SI,TextP
        mov dh,0x0a
        call DrawImage

        xor di,di
        mov di,750
        mov bx,di
        mov SI,TextA
        mov dh,0x0a
        call DrawImage

        xor di,di
        mov di,767
        mov bx,di
        mov SI,TextC
        mov dh,0x0a
        call DrawImage

        xor di,di
        mov di,784
        mov bx,di
        mov SI,TextE
        mov dh,0x0a
        call DrawImage

        xor di,di
        mov di,813
        mov bx,di
        mov SI,TextP
        mov dh,0x0a
        call DrawImage

        xor di,di
        mov di,830
        mov bx,di
        mov SI,TextO
        mov dh,0x0a
        call DrawImage

        xor di,di
        mov di,847
        mov bx,di
        mov SI,TextN
        mov dh,0x0a
        call DrawImage

        xor di,di
        mov di,864
        mov bx,di
        mov SI,TextG
        mov dh,0x0a
        call DrawImage
        ret
   
PutTextS:
        mov byte [Row],7
        mov di,60234
        mov bx,di
        mov si,LetterB
        mov dh,0ah
        call DrawImage

        mov di,60241
        mov bx,di
        mov si,LetterY
        mov dh,0ah
        call DrawImage
    
        mov di,60255
        mov bx,di
        mov si,LetterC
        mov dh,0ah
        call DrawImage
     
        mov di,60262
        mov bx,di
        mov si,LetterR
        mov dh,0ah
        call DrawImage

        mov di,60269
        mov bx,di
        mov si,LetterA
        mov dh,0ah
        call DrawImage

        mov di,60276
        mov bx,di
        mov si,LetterI
        mov dh,0ah
        call DrawImage

        mov di,60284
        mov bx,di
        mov si,LetterG
        mov dh,0ah
        call DrawImage

        mov di,60298
        mov bx,di
        mov si,LetterB
        mov dh,0ah
        call DrawImage

        mov di,60305
        mov bx,di
        mov si,LetterA
        mov dh,0ah
        call DrawImage

        mov di,60312
        mov bx,di
        mov si,LetterM
        mov dh,0ah
        call DrawImage

        mov di,60319
        mov bx,di
        mov si,LetterF
        mov dh,0ah
        call DrawImage

        mov di,60326
        mov bx,di
        mov si,LetterO
        mov dh,0ah
        call DrawImage

        mov di,60333
        mov bx,di
        mov si,LetterR
        mov dh,0ah
        call DrawImage

        mov di,60340
        mov bx,di
        mov si,LetterD
        mov dh,0ah
        call DrawImage

        mov di,60354
        mov bx,di
        mov si,Two
        mov dh,0ah
        call DrawImage

        mov di,60361
        mov bx,di
        mov si,Zero
        mov dh,0ah
        call DrawImage
   
        mov di,60368
        mov bx,di
        mov si,Zero
        mov dh,0ah
        call DrawImage

        mov di,60375
        mov bx,di
        mov si,Three
        mov dh,0ah
        call DrawImage

        mov di,60385
        mov bx,di
        mov si,CopyrightSymbol
        mov dh,0ah
        call DrawImage
        ret

Row      DB         0
TextA    DW         0FFFFh,08001h,08001h,08001h,087E1h,08421h,08421h,087E1h
         DW         08001h,08001h,087E1h,08421h,08421h,08421h,08421h,0FC3Fh
TextC    DW         0FFFEh,08002h,08002h,087E2h,0843Eh,08400h,08400h,08400h
         DW         08400h,08400h,0843Eh,08422h,087E2h,08002h,08002h,0FFFEh
TextE    DW         0FFFFh,08001h,08001h,087FFh,08400h,08400h,087FEh,08002h
         DW         08002h,087FEh,08400h,08400h,087FFh,08001h,08001h,0FFFFh
TextS    DW         0FFFFh,08001h,08001h,087E1h,0843Fh,08400h,087FFh,08001h
         DW         08001h,0FFE1h,00021h,0FC21h,087E1h,08001h,08001h,0FFFFh
TextM1   DW         0FFFFh,08000h,08000h,08000h,09FE7h,09024h,09024h,09024h
         DW         09024h,09024h,09024h,09024h,09024h,09024h,09024h,0F03Ch
TextM2   DW         0FF00h,00100h,00100h,00100h,0F900h,00900h,00900h,00900h
         DW         00900h,00900h,00900h,00900h,00900h,00900h,00900h,00F00h
TextP    DW         0FFFFh,08001h,08001h,087F9h,08409h,08409h,08409h,087F9h
         DW         08001h,08001h,087FFh,08400h,08400h,08400h,08400h,0FC00h 
TextO    DW         0FFFFh,08001h,08001h,087E1h,08421h,08421h,08421h,08421h
         DW         08421h,08421h,08421h,08421h,087E1h,08001h,08001h,0FFFFh  
TextN    DW         0FFFFh,08001h,08001h,087E1h,08421h,08421h,08421h,08421h
         DW         08421h,08421h,08421h,08421h,08421h,08421h,08421h,0FC3Fh
TextG    DW         0FFFEh,08002h,08002h,087E2h,0843Eh,08400h,08400h,08400h
         DW         0847Fh,08441h,08463h,08422h,087E2h,08002h,08002h,0FFFEh
Two      DW         3800h,4400h,0400h,1800h,2000h,4000h,7c00h
Zero     DW         3800h,4400h,4c00h,5400h,6400h,4400h,3800h
Three    DW         3800h,4400h,0400h,1800h,0400h,4400h,3800h
LetterA  DW         3800h,4400h,4400h,7c00h,4400h,4400h,4400h
LetterB  DW         7800h,4400h,4400h,7800h,4400h,4400h,7800h
LetterC  DW         3800h,4400h,4000h,4000h,4000h,4400h,3800h
LetterD  DW         7800h,4400h,4400h,4400h,4400h,4400h,7800h
LetterE  DW         7c00h,4000h,4000h,7800h,4000h,4000h,7c00h
LetterF  DW         7c00h,4000h,4000h,7800h,4000h,4000h,4000h
LetterG  DW         3800h,4400h,4000h,5c00h,4400h,4400h,3800h
LetterH  DW         4400h,4400h,4400h,7c00h,4400h,4400h,4400h
LetterI  DW         7c00h,1000h,1000h,1000h,1000h,1000h,7c00h
LetterJ  DW         0400h,0400h,0400h,0400h,0400h,4400h,3800h
LetterK  DW         4400h,4800h,5000h,6000h,5000h,4800h,4400h
LetterL  DW         4000h,4000h,4000h,4000h,4000h,4000h,7c00h
LetterM  DW         4400h,6c00h,5400h,4400h,4400h,4400h,4400h
LetterN  DW         4400h,6400h,5400h,4c00h,4400h,4400h,4400h
LetterO  DW         3800h,4400h,4400h,4400h,4400h,4400h,3800h
LetterP  DW         7800h,4400h,4400h,7800h,4000h,4000h,4000h
LetterQ  DW         3800h,4400h,4400h,4400h,4400h,4c00h,3c00h
LetterR  DW         7800h,4400h,4400h,7800h,4400h,4400h,4400h
LetterS  DW         3800h,4400h,4000h,3800h,0400h,4400h,3800h
LetterT  DW         7c00h,1000h,1000h,1000h,1000h,1000h,1000h
LetterU  DW         4400h,4400h,4400h,4400h,4400h,4400h,3800h
LetterV  DW         4400h,4400h,4400h,4400h,4400h,2800h,1000h
LetterW  DW         4400h,4400h,4400h,4400h,5400h,6c00h,4400h
LetterX  DW         4400h,4400h,2800h,1000h,2800h,4400h,4400h
LetterY  DW         4400h,4400h,2800h,1000h,1000h,1000h,1000h
LetterZ  DW         7c00h,0400h,0800h,1000h,2000h,4000h,7c00h
CopyrightSymbol DW  1e00h,2100h,4c80h,4880h,4c80h,2100h,1e00h

NOTE: This is code to be easy to understand, you need to optimise to use in your OS, also note its fasm, so bits may need converting for nasm.

os64dev · Post by **os64dev** » Thu Feb 01, 2007 3:46 pm

jeez, now i know why i like to program in C/C++, no harm intended dex, but it really is a nice example though it is for real-mode and not for protected mode, however the concept doesn't change much.

regards

pcmattman · Post by **pcmattman** » Thu Feb 01, 2007 11:51 pm

I'm coding in Assembly and using Real Mode.

Combuster · Post by **Combuster** » Fri Feb 02, 2007 3:51 am

os64dev wrote:jeez, now i know why i like to program in C/C++, no harm intended dex, but it really is a nice example though it is for real-mode and not for protected mode, however the concept doesn't change much.

Well, the original poster did ask for realmode assembly... And besides, what does it matter what language its in if it works?