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;* Colors - Alters screen colors within a specified area by using bit
;* or move operations on display attribute bytes in video memory.
;*
;* Shows:   Instructions - not     rol     ror     and     xor     or
;*
;* Params:  Logic - Code number, 0 = NOT    2 = ROR     4 = XOR    6 = MOV
;*                               1 = ROL    3 = AND     5 = OR
;*          Attr - Attribute mask
;*          Row1 - Row at top of window
;*          Col1 - Column at left edge of window
;*          Row2 - Row at bottom of window
;*          Col2 - Column at right edge of window
;*
;* Return:  None
 
Colors  PROC USES ds si,
        Logic:WORD, Attr:WORD, Row1:WORD, Col1:WORD, Row2:WORD, Col2:WORD
 
        GetVidOffset Row1, Col1         ; Get offset in video segment
        inc     ax
        mov     si, ax                  ; SI = offset for 1st attr byte
        mov     bx, Row2
        sub     bx, Row1
        inc     bx                      ; BX = number of window rows
        mov     cx, Col2
        sub     cx, Col1
        inc     cx                      ; CX = number of columns
 
        mov     ds, vconfig.sgmnt       ; DS = video segment
        mov     ax, Attr                ; AL = mask for and, xor, and or
 
        .REPEAT
        push    si                      ; Save ptr to start of line
        push    cx                      ;   and number of columns
 
; Disable CGA video prior to memory access to avoid screen snow. (See the
; WinOpen and StrWrite procedures for further discussions on CGA snow.)
 
        .IF     vconfig.adapter == CGA  ; If CGA adapter:
        INVOKE  DisableCga              ; Yes?  Disable video
        .ENDIF
 
        cmp     Logic, 1                ; Rotate left?
        jl      c_not                   ; If less, do NOT
        je      c_rol                   ; If equal, do ROL
        cmp     Logic, 3                ; And?
        jl      c_ror                   ; If less, do ROR
        je      c_and                   ; If equal, do AND
        cmp     Logic, 5                ; Or?
        jl      c_xor                   ; If less, do XOR
        je      c_or                    ; If equal, do OR
c_mov:
        mov     BYTE PTR [si], al       ; MOV attr parameter
        add     si, 2                   ;   into attribute byte
        loop    c_mov
        jmp     c_done
c_or:
        or      BYTE PTR [si], al       ; OR with attr parameter
        add     si, 2
        loop    c_or
        jmp     c_done
c_xor:
        xor     BYTE PTR [si], al       ; XOR with attr parameter
        add     si, 2
        loop    c_xor
        jmp     c_done
c_and:
        and     BYTE PTR [si], al       ; AND with attr parameter
        add     si, 2
        loop    c_and
        jmp     c_done
c_ror:
        ror     BYTE PTR [si], 1        ; Rotate right 1 bit
        add     si, 2
        loop    c_ror
        jmp     c_done
c_rol:
        rol     BYTE PTR [si], 1        ; Rotate left 1 bit
        add     si, 2
        loop    c_rol
        jmp     c_done
c_not:
        not     BYTE PTR [si]           ; Flip bits
        add     si, 2
        loop    c_not
c_done:
        .IF     vconfig.adapter == CGA  ; If CGA:
        INVOKE  EnableCga               ; Reenable CGA video
        .ENDIF
 
        pop     cx                      ; Recover number of columns
        pop     si                      ; Recover offset for start of line
        add     si, 160                 ; Point to start of next line
        dec     bx                      ; Decrement row counter
        .UNTIL  zero?                   ; Loop while rows remain
        ret
 
Colors  ENDP
                                    -♦-