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;* StrInput - Gets input string from keyboard using BIOS. Signals idle
;* state by calling interrupt 28h while polling for keypress, making
;* the procedure useful in TSR programs. Terminates when Enter or Esc
;* keys pressed.
;*
;* Shows:   DOS interrupt - Interrupt 28h (DOS Idle Interrupt)
;*
;* Params:  Row - Row coordinate
;*          Col - Column coordinate
;*          Max - Maximum allowable string length
;*          Sptr - Pointer to string
;*
;* Return:  Short integer with terminating char
 
StrInput PROC USES ds si,
        Row:WORD,
        Col:WORD,
        Max:WORD,
        Sptr:PBYTE
 
        LoadPtr ds, si, Sptr            ; DS:SI points to string
        add     Max, si
        dec     Max                     ; MAX now points to string limit
 
        .WHILE  1                       ; Get key until break or continue
loop1:
        INVOKE  StrWrite,               ; Display input string
                Row,
                Col,
                si
 
        mov     bx, si
        mov     dx, Col                 ; DL = cursor column
 
        .WHILE  (BYTE PTR [bx] != 0)    ; Scan string for null terminator
        inc     bx                      ; Else try next character
        inc     dx                      ;   and increment cursor column
        .ENDW
 
        ; Set cursor position, pass row and column (DX)
        INVOKE  SetCurPos,
                Row,
                dx
 
        .REPEAT
        int     28h                     ; Signal idle state
        mov     ah, 1
        int     16h                     ; Key waiting?
        .CONTINUE .IF zero?
        sub     ah, ah
        int     16h                     ; Yes?  Get key
 
        cmp     ah, LEFT                ; Left arrow key?
        je      backspace               ; Treat like backspace
        .UNTIL  al != 0                 ; Ignore all other special keys
 
        .BREAK  .IF al == ESCAPE        ; Exit if Esc key
        .BREAK  .IF al == CR            ; Exit if Return key
 
        .IF     al == BACKSP            ; If backspace or left, handle it
backspace:
        cmp     bx, si                  ; At first letter?
        jbe     loop1                   ; Yes?  Ignore backspace
        dec     bx                      ; No?  Point to preceding char
        dec     dx                      ; Decrement column
        mov     BYTE PTR [bx], ' '      ; Blank char
        push    bx                      ; Preserve pointer
        INVOKE  StrWrite,               ; Overwrite last char with blank
                Row,
                dx,
                bx
 
        pop     bx
        mov     BYTE PTR [bx], 0        ; Make last char the new terminator
        .CONTINUE
        .ENDIF
 
        .CONTINUE .IF bx > Max          ; Ignore key if too many letters
        sub     ah, ah
        mov     [bx], ax                ; Store letter and null terminator
        .ENDW
 
        ret
 
StrInput ENDP
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