Correction for Scroll SUB in GENERAL.BAS, UI Toolbox (69111)


The information in this article applies to:

  • Microsoft Basic Professional Development System for MS-DOS 7.0
  • Microsoft Basic Professional Development System for MS-DOS 7.1
This article was previously published under Q69111

SYMPTOMS

The subprogram Scroll within GENERAL.BAS will not display the correct attributes if you select a negative number for "lines" when you want to scroll the window down.

STATUS

A correction for this problem is shown below. (Scrolling in the up direction displays the correct attributes, and needs no correction.)

This correction applies to the User Interface (UI) Toolbox in Microsoft Basic Professional Development System (PDS) versions 7.00 and 7.10 for MS-DOS.

MORE INFORMATION

The MS-DOS Interrupt call 16 hex with function 7 or 6 requires that the BX register be set with the color attribute. The bits 6 through 4 are set to the desired background attribute. The following formula shifts this attribute into the correct location in the word register BX: 
   regs.bx = 256 * (attr MOD 8) * 16
The original code for subprogram Scroll has the following attributes set for the BX register: 
   regs.bx = 256 * attr
The following excerpt is from Scroll with the correct modifications: 
SUB Scroll (row1, col1, row2, col2, lines, attr)
          .
          .
          .
     MAXCOL THEN
        DIM regs AS RegType
        IF lines < 0 THEN
            regs.ax = 256 * 7 + (-lines)
           'regs.bx = 256 * attr                 <=== old code
            regs.bx = 256 * (attr MOD 8) * 16   '<=== change to this
            regs.cx = 256 * (row1 - 1) + (col1 - 1)
            regs.dx = 256 * (row2 - 1) + (col2 - 1)
        ELSE
            regs.ax = 256 * 6 + lines                  'AH = 06
            regs.bx = 256 * (attr MOD 8) * 16
            regs.cx = 256 * (row1 - 1) + (col1 - 1)
            regs.dx = 256 * (row2 - 1) + (col2 - 1)
        END IF
        INTERRUPT 16, regs, regs
    END IF
END SUB
Modification Type:MinorLast Reviewed:8/16/2005
Keywords:KB69111
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