Q69111: Correction for Scroll SUB in GENERAL.BAS, UI Toolbox

Article: Q69111
Product(s): See article
Version(s): 7.00 7.10
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S910115-118 buglist7.00 buglist7.10 | mspl13_basic
Last Modified: 14-FEB-1991

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. 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.

The 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

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