This is my function of print a dot(cx, dx) using video memory. After calculate the offset di, I don't know how to change the color of the dot, so I ask gpt. Gpt gives me this way but it only shows white dot. How can I generate dots of different color?
vmem1 PROC
mov ax, 0A000h ; video memory start point
mov es, ax
;offset=y*(640/8)+(x/8)
mov ax, dx
mov bx, 80
mul bx
mov di, ax
mov ax, cx
mov bx, 8
div bx
add di, ax ; di=offset
mov dx, 3c4h
mov al, 2
out dx, al
inc dx
mov al, 2
out dx, al
mov al, 4
mov es:[di], al
ret
vmem1 ENDP
Now I can only show a white dot. I hope to generate other colors.
Where you have:
mov al, 4
mov es:[di], al
where you should have:
mov al,es:[di]
mov al, 4
mov es:[di], al
The "dummy" read loads the latch register as described at http://www.osdever.net/FreeVGA/vga/vgamem.htm#read
The default palette assigns RED to index 4.
I would not put my faith in the rest of the code either to be honest, it is not clear to me that the manipulation of the map mask register is necessary or correct. The bit mask register on the other hand is clearly necessary to write a single pixel without affecting adjacent pixels.
Real examples of such operations are numerous and no harder to find and, I suggest, more reliable and better documented than AI generated nonsense. For example the putpixel example at https://www.fysnet.net/modex.htm for example:
; on entry X,Y = location and C = color (0-15)
putpixel proc near uses ax bx cx dx
; byte offset = Y * (horz_res / 8) + int(X / 8)
mov ax,Y ; calculate offset
mov dx,80 ;
mul dx ; ax = y * 80
mov bx,X ;
mov cl,bl ; save low byte for below
shr bx,03 ; div by 8
add bx,ax ; bx = offset this group of 8 pixels
mov dx,03CEh ; set to video hardware controller
and cl,07h ; Compute bit mask from X-coordinates
xor cl,07h ; and put in ah
mov ah,01h ;
shl ah,cl ;
mov al,08h ; bit mask register
out dx,ax ;
mov ax,0205h ; read mode 0, write mode 2
out dx,ax ;
mov al,es:[bx] ; load to latch register
mov al,Color
mov es:[bx],al ; write to register
ret
putpixel endp
X dw 00h
Y dw 00h
Color db 00h
Also you would do well to understand the VGA hardware in detail (so at least you might understand what the AI did - and when it doesn't work, why). It is well documented at http://www.osdever.net/FreeVGA/vga/vga.htm for example.