mode13.asm

start:          call    mode13          ; Set mode 13
repeat_row:     mov     ax, [posx]
                cmp     ax, 320         ; Check if posx >= 320
                jz      end_xloop       ; Stop
                mov     al, [color]
                mov     cx, [posx]
                mov     dx, [posy]
                call    setpixel        ; Set pixel at posx, posy with color
                inc     byte [color]    ; color += 1
                inc     word [posx]     ; posx += 1
                jmp     repeat_row      ; Repeat
end_xloop:      mov     word [posx], 0  ; Reset posx
                inc     word [posy]     ; posy += 1
                mov     ax, [posy]
                cmp     ax, 200         ; Check if posy >= 200
                jne     repeat_row      ; Repeat
                call    waitkey
                call    exit

mode13:         mov     ax, 13h
                int     10h             ; Switch to gfx mode
                ret

; cx = X, dx = Y, bh = color                
setpixel:       mov     ah, 0ch
                mov     bh, 0
                int     10h             ; Set pixel top-left
                ret
                
waitkey:        mov     ax, 0
                int     16h             ; Wait for keyboard
                ret

exit:           mov     ax, 3h
                int     10h             ; Switch to text mode
                int     20h             ; Terminate
                ret


color:          db      1
posx:           dw      2
posy:           dw      2