printing a sentence on screen-CodePudding

I need to print a full sentence on screen with the ah, 09h technique. I don't now why it doesn't show up on screen.

message db 'game over, to play again press y$'
PROC GAMEOVER
push dx
    call cleanscreen
    mov dx, offset message
    mov ah,9h
    int 21h
    mov ah,0
    int 16h
    cmp al, 'y'
    jne line
        CALL STARTGAME
    line:
    pop dx
RET 
ENDP GAMEOVER

proc cleanscreen ; cleans the screen
    push cx
    push bx
    mov cx,4000d
    mov bx,0
    clean:
        mov [byte ptr es:bx],0
        inc bx
    loop clean
    pop bx
    pop cx
    ret
endp cleanscreen

CodePudding user response：

Look at the cleanscreen proc:

proc cleanscreen ; cleans the screen
 push cx
 push bx
 mov cx,4000d
 mov bx,0
clean:  mov [byte  ptr es:bx],0
 inc bx
 loop clean
 pop bx
 pop cx
 ret
endp cleanscreen

The screen is setup for the 80x25 16-color text mode. When you clear the screen storing all zeroes in it, it means that all the character cells get filled with ASCII code 0 (which is a space character) and attribute 00h (which is BlackOnBlack). The important thing here is that the DOS.PrintString function 09h does not care about the attributes already present on the screen, and neither does it output any new color information. Thus the characters of your text get written to screen fine but you don't get to see any of it because of the black foreground color and the black background color.

Write the proc this way:

proc cleanscreen ; cleans the screen
    push ax
    push cx
    push di
    mov  ax, 0720h  ; WhiteOnBlack space character
    mov  cx, 2000   ; 80*25
    xor  di, di
    rep  stosw      ; write CX words starting at [es:di] 
    pop  di
    pop  cx
    pop  ax
    ret
endp cleanscreen