Graphics mode in assembly 8086
I have a variable that is called average and in my DATASEG, it changes every time because the user enters a different input every time. What I want to do is to go to the graphics mode (VGA) and then print there Your average is: and then the average I know how to change to the graphics mode like this:
mov ax, 13h
int 10h
After printing the average I want to print below if the average is above 75 You are a good student, keep up the good work and if not. Don't worry you will get better! Thanks in advance.
Answer
I am assuming: PC VGA x86 MS DOS platform
It does not really matter if real or emulated unless you want low level IO access which might not work properly on emulation like DOSBOX ...
Video/Text modes
So to switch between video and text modes you need to use VGA BIOS:
mov ax,mode ; here select which mode you want int 16 ; this calls EGA/VGA/VESA BIOSThere are many video modes here two very important ones:
mode | type | segment | resolution | align ---------------------------------------------------- 03 | text | B800h | 80x25 chars | 2 Byte 19 | video | A000h | 320x200x256 colors | 1 ByteIn video mode
19you print/peek pixel by accessing memory at segmentA000hwhere offset is computed like this:offset = 320*y + xThe
320x200mode fits entirely into64 KBytesegment so you do not need to switch pages. This makes it ideal for simple asm gfx programs ....Mode
3is text mode where each character has2 BYTEsone is color and the other is extended ASCII code. Again print/peek is done by accessingWORDat segmentB800hwhere offset is:offset = (80*y + x) * 2Not sure what order is the two bytes in anymore it was ages ago but you can easily test if writing
Aat0B800:0000will renderAin top left corner or0B800:0001instead. IIRC colors in text modes are just first 16 colors from palette and the color byte encodes ink paper brightness and flash. This text mode is also the default mode your MS-DOS shell is working in so you should set it back before program exit.So your program should look like this:
start: mov ax,19 ; set video mode int 16 mainloop: ; here your stuff exit: mov ax,3 int 16 retPrinting strings
For starters you can combine text and video modes ... Like I do here:
it is a simple game where menus are in text mode (where printing is easy and just matter of copying the string into VRAM) and the sprite graphics game is on
320x200x256cvideo mode.When you want to print in gfx mode you first need to have some Font in the memory. If you look at the EGA/VGA BIOS documentation you can obtain the font located in EGA/VGA ROM and use directly that. I also created this image (IIRC using Trident 9000 256/512KB VGA font) which I use as a mono-spaced font for OpenGL and other stuff (where accessing VGA BIOS is not possible or wanted)...
Here GLSL example of using it for printing You can port it to CPU/VGA/asm but the printing on CPU is much more simpler no need for such horrible things like in GLSL fragment.
So you just need to compute image position from ASCII code and copy its pixels into VRAM. Of coarse having bitmap in asm is not easy and much easier is to have it directly in binary form (as set of
db) so you can write some simple C++ (or whatever) script which loads image and converts it to asm source ...Here is some ancient
320x200x256 colorsprinting lib I wrote in NASM ages ago (using EGA/VGA Font directly):;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;GFX mode 13h print librrary ver:1.0 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;txti init font adress ;char cx=color,al=ASCII,scr:di<=al ;cl=ch => no background ;print scr:di <= ds:si ,cx=color cl=ch => no background ;printl scr:di text after call ,cx=color ... ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; txti: pusha ;init font adress push es mov ax,1130h ; VGA BIOS - font info mov bh,3 ; font 8 x 8 pixels int 10h ; ES:BP returns font address mov [cs:fonts],es ;get font adr mov [cs:fonto],bp pop es popa ret fonts dw 0 ; font address for printing ... fonto dw 0 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; char: pusha ;cx=color,al=ASCII,scr:di<=al ;cl=ch => no background push ds push es push word 0A000h pop es sub ah,ah shl ax,3 mov ds,[cs:fonts] mov si,[cs:fonto] add si,ax mov dh,8 .char0: mov dl,8 lodsb mov ah,al .char1: mov al,cl rcl ah,1 jc .char2 mov al,ch .char2: cmp cl,ch jz .char3 mov [es:di],al .char3: inc di dec dl jnz .char1 add di,320-8 dec dh jnz .char0 pop es pop ds popa ret ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; print: pusha ;scr:di <= ds:si ,cx=color cl=ch => no background .l0: lodsb or al,al jz .esc call char add di,8 jmp short .l0 .esc: popa ret ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; printl: mov [cs:.dat],si ;scr:di text after call ,cx=color ... pop si push ax push di push ds push cs pop ds .l0: lodsb or al,al jz .esc call char add di,8 jmp short .l0 .esc: pop ds pop di pop ax push si add di,9*320 mov si,[cs:.dat] ret .dat: dw 0 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;; end. ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;So to use it the program should be like:
start: call txti ; just once at program startup mov di,50+320*10 mov cx,127 call printl db 'SPEKTRA software & hardware',0 mov di,50+320*30 mov cx,127 call printl db 'print test',0The
printis used by settingds,siso it points to your null terminated string. As you can seeprintldoes not need that as it uses string located directly after theprintlcall and program continues after it ... This way you do not need pointer setting instructions nor any additional labes ... The colors are incl,chone is ink and the other is paper. Ifcl==chthen no paper will be rendered just the ink pixels that is useful if you got image or gfx background behind the text ... The values for colors might not be visible I taken the colors from one of mine games which sets its own palette so if nothing is visible try to set differentcl,chlikemov cx,0305hTake a look at this:Print numbers
Printing non negative integer number value is a matter of dividing the number by base (10) and printing the
remainder + '0'in reverse order as characters ...In
hexit is even easier as each digit corresponds to nibble<0-15>so for 16 bit in you take highest 4 bits convert to char either byxlattable or by adding'0'or'A'depending if value is below10... so no divisions just bit shift/mask ... print the char and shift left the value by 4 bits to process next digit ...btw in gfx modes is often much nicer and user friendly to instead of printing a value as a number render a progress bar like stuff instead which is much much more easier ... collapses to single loop rendering H or V line ... like
REP STOSB:) ...VESA
For Super VGA video modes above 320x200x8bpp we need to add page crossings of data as VRAM does not fit 64KByte segment anymore. I strongly suggest to use VESA (VBE) api for this. The idea is to have the
A000:0000segment be mapped to certain segment of the VRAM which we can change at any time. For more info on how see these:In case your gfx card does not have VESA/VBE for most cards its possible to add it by using UniVBE 5.3 or newer utility under MS-DOS.