How to read image file and display on screen in windows tasm dosbox

Question

Im currently learning graphical programming in tasm using dosbox. Ive been using a bunch of loops to draw square blocks of pixels and its really hard. I want to know if theres a way to read an image and display it. I know how to read a txt file maybe this is a start. Pls help

Answer 1

You need to write/use image loader or use your own image file format. BMP may look simple but has too much in it like compression pixel formats etc but you still can focus on a specific type of BMP and ignore all the others...

Back in the days of MS-DOS I was using 256 color PCX images with palette as I used 256 color video modes. Here NASM LINEZ game example:

• Color Lines - simple game in C++/the checking algorithm

see the pcx: subroutine. It decodes loaded PCX file from memory ds:0 to raw VGA image at es:di. Beware it does support just 64 KByte size limit !!! Now to visualize the image you would have to copy es:di content into VideoRAM (assuming A000:0000) for example with rep movsd or you can set es:di to it in the first place (but that could flicker).

This PCX loader however does not use palette from the image so you need to encode it ... (the routines to change VGA palette are included in the source you just need to extract the RGB values from PCX I think it was at the end of file) Look here:

• my C++ PCX loader with palette

if converts PCX to 32bit raw image.

For more info about MS-DOS game programing see PCGPE 1.0

Here another game example (TASM) which uses own image file-format:

• What is the best way to move an object on the screen?

It has text menues, binary file access, 320x200 sprite graphics, 3 human players

[Edit1] New code

I removed the old code example and instead I created compilable and working 8bit PCX with color palette viewer in TASM. It uses VESA 800x600x256 colors mode (103h).

The image must fit into screen and its file size must be less than 64 KByte !!!

I did not add any checks or error messages ... It simply loads file image.pcx and displays it on VESA then wait on key hit end exit. Here the TASM source:

PCX.ASM

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
    .386
    IDEAL
    MODEL TINY
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
    DATASEG
file:   db 'image.pcx',0    ;filename to load
buff:       
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
    CODESEG
    STARTUPCODE

    scrxs   equ 800
    scrys   equ 600
    mov ax,103h ; VESA 800x600x256
    call    vesamod
    mov al,0
    call    vesapag

;   scrxs   equ 320
;   scrys   equ 200
;   mov ax,19   ; VGA 320x200x256
;   int 10h

    lea dx,[file]   ; load PCX into DS:buff, CX bytes
    call    fopen
    lea dx,[buff]
    mov cx,64000    ; some max value to fit into DS segment
    call    fread       ; CX is PCX real size
    call    fclose

    lea si,[buff]   ; decode directly to VRAM
    mov ax,0A000h
    mov es,ax
    mov di,0
    call    pcx
mainl0:
    mov ax,256  ; test keyboard
    int 16h
    jz  mainl0
    sub ax,ax   ; clear key buffer
    int 16h

    mov ax,3    ;|VGA 80x25 text
    int 16
    ret
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
vesamod:pusha               ;set VESA videomode ax
    mov     bx,ax
    mov     ax,4f02h
    int     16
    popa
    ret
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
vesapag:pusha               ;al=page  switch vesa video page window A
    mov [cs:scrpag],al
    mov     dl,al
    sub     dh,dh
    sub     bx,bx
    mov     ax,4f05h    ; window A
    int     16
    popa
    ret
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;  .386P
scrpag  db 0
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;  .386P
hand    dw 0        ;###    handler...
ferr    db 0        ;###    DOS error code
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
fopen:  pusha       ;DS:DX = file name, [hand] <= file handle
    mov ax,3D02h
    int 21h
    mov bl,0
    jnc fopen0
    mov bl,al
    sub ax,ax
fopen0: mov [cs:hand],ax
    mov [cs:ferr],bl
    popa
    ret
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
fclose: pusha       ;[hand] = file handle
    mov bx,[cs:hand]
    mov ah,3eh
    int 21h
    mov bl,0
    jnc fclose0
    mov bl,al
    sub ax,ax
fclose0:mov [cs:ferr],bl
    mov [cs:hand],ax
    popa
    ret
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
fread:  pusha       ;DS:DX = adr, CX = lenght, [hand] = hand, CX => read
    mov bx,[cs:hand]
    mov ah,3Fh
    int 21h
    mov bl,0
    jnc fread0
    mov bl,al
    sub ax,ax
fread0: mov [cs:ferr],bl
    mov [cs:freadsz],ax
    popa
    mov cx,[cs:freadsz]
    ret
freadsz dw 0
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pcx:    pusha           ;decode pcx at ds:si to es:di cx = PCX size
    push    ds
    push    es
    push    ecx
    push    edx

    push    si      ;set palette
    add si,cx
    sub si,768
    sub ax,ax   
pall0:  mov dx,3C8h
    mov al,ah
    out dx,al
    inc dx
    lodsb
    shr al,2
    out dx,al
    lodsb
    shr al,2
    out dx,al
    lodsb
    shr al,2
    out dx,al
    inc ah
    jnz pall0
    pop si

    mov ax,[ds:si+8]    ;get xs
    sub ax,[ds:si+4]
    inc ax
    mov [cs:pcxxs],ax
    mov [cs:pcxx],ax

    mov ax,[ds:si+10]   ;get ys
    sub ax,[ds:si+6]
    inc ax
    mov [cs:pcxys],ax   

    mul [cs:pcxxs]
    push    dx
    push    ax
    pop edx
    add si,128      ;src start after pcx header
    sub ecx,ecx     ;RLE decoder of PCX
pcxl0:  lodsb
    mov cx,1
    cmp al,192
    jb  pcxr0
    mov cl,al
    and cl,63
    lodsb
pcxr0:  mov bx,cx
pcxl1:  call    point

    dec [cs:pcxx]   ;correct next screen line position if end of PCX line
    jnz pcxr1   
    mov ax,[cs:pcxxs]
    mov [cs:pcxx],ax
    neg ax
    add ax,scrxs
    add di,ax
    jnc pcxr1
    ; page swith
    mov al,[cs:scrpag]
    inc al
    call    vesapag

pcxr1:  loop    pcxl1
    mov cx,bx
    sub edx,ecx
    jz  pcxesc
    jnc pcxl0

pcxesc: pop edx
    pop ecx
    pop es
    pop ds
    popa
    ret
pcxxs   dw  0   ;PCX resolution
pcxys   dw  0
pcxx    dw  0   ;actual X coordinate 
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
point:  mov [es:di],al      ;point      ;estosb 
    inc di
    jnz pntesc
    ; page swith
    mov al,[cs:scrpag]
    inc al
    call    vesapag
pntesc: ret
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
    END
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

So take any image up to 800x600 convert it to 256 color PCX with palette and rename it to image.pcx. Then place it to your *.com file and run. I compiled it with Volcov commander extension script vc.ext like this:

asm:@c:\language\compil\tasm\tasm !.! /ic:\language\source\tasm\inc
    @c:\language\compil\tasm\tlink !.obj /t /x
    @del !.obj

so each time I hit the enter on any asm file it will compile. Just change the paths and if you are not targeting *.com files then change the /t switch accordingly. Here preview from my DOSBox: