How to Scroll Text in Basic Protected Mode Program Using API (63956)

MORE INFORMATION

Basic 6.00 and 6.00b and Basic PDS 7.00 and 7.10 can directly call OS/2 API functions by linking with the appropriate library. This library is called DOSCALLS.LIB for Basic 6.00 and 6.00b and OS2.LIB for Basic PDS 7.00 and 7.10.

The API functions VioScrollUp(), VioScrollDn(), VioScrollLf(), and VioScrollRt() all require the following parameters:

   Parameter   Description
   ---------   -----------

   WORD        y (row) coordinate of upper left corner
   WORD        x (column) coordinate of upper left corner
   WORD        y (row) coordinate of lower right corner
   WORD        x (column) coordinate of lower right corner
   WORD        Number of lines or columns to scroll
   PTR WORD    Contains character (lower byte) and attribute
               (upper byte) used to fill blanked lines or columns
   WORD        Video handle (0 = default)
				

The first four parameters specify the rectangle in which the scrolling is to take place. Any area outside this rectangle is not scrolled. The sixth parameter specifies the character and attribute to use for the new lines or columns created behind the scrolling text. Note that a WORD in Basic is an INTEGER, and any parameters preceded by the word "PTR" must be passed using the SEG clause in the DECLARE statement; BYVAL is used otherwise. The default for Basic is to pass by reference (not BYVAL).

The following program (SCROLL.BAS) displays a message on the screen and allows you to scroll the message up, down, left, or right using the cursor keys. Note that this example uses only the cursor keys on the numeric keypad, not the extended cursor keys. Any part of the message that is scrolled off the screen is lost. Press the ESC key to terminate execution.

To compile and link the program, enter the following lines at the OS/2 command prompt:

   bc scroll /v ;
   link scroll;
				

Code Example

'SCROLL.BAS
DEFINT A-Z

'Declarations for OS/2's Vio scroll functions.
DECLARE FUNCTION VioScrollUp (BYVAL Y1      AS INTEGER,_
                              BYVAL X1      AS INTEGER,_
                              BYVAL Y2      AS INTEGER,_
                              BYVAL X2      AS INTEGER,_
                              BYVAL Lines   AS INTEGER,_
                              SEG   FillNew AS INTEGER,_
                              BYVAL Handle  AS INTEGER)

DECLARE FUNCTION VioScrollLf (BYVAL Y1      AS INTEGER,_
                              BYVAL X1      AS INTEGER,_
                              BYVAL Y2      AS INTEGER,_
                              BYVAL X2      AS INTEGER,_
                              BYVAL Lines   AS INTEGER,_
                              SEG   FillNew AS INTEGER,_
                              BYVAL Handle  AS INTEGER)

DECLARE FUNCTION VioScrollRt (BYVAL Y1      AS INTEGER,_
                              BYVAL X1      AS INTEGER,_
                              BYVAL Y2      AS INTEGER,_
                              BYVAL X2      AS INTEGER,_
                              BYVAL Lines   AS INTEGER,_
                              SEG   FillNew AS INTEGER,_
                              BYVAL Handle  AS INTEGER)

DECLARE FUNCTION VioScrollDn (BYVAL Y1      AS INTEGER,_
                              BYVAL X1      AS INTEGER,_
                              BYVAL Y2      AS INTEGER,_
                              BYVAL X2      AS INTEGER,_
                              BYVAL Lines   AS INTEGER,_
                              SEG   FillNew AS INTEGER,_
                              BYVAL Handle  AS INTEGER)

Y1 = 0    'Set the coordinates of the window scrolling area to define
X1 = 0    'the whole screen (assuming 25 rows and 80 columns).
Y2 = 24
X2 = 79

Lines    = 1       'Scroll one line at a time.
FillNew  = 20010   'Fill the new lines/columns with yellow asterisks
                   'on a red background.
Handle   = 0       'Specifies the default OS/2 screen group.

CLS                 'Clear screen and display the message to scroll.
LOCATE 12, 30
PRINT "Use arrows on numeric keypad to scroll."
PRINT "Hit Esc to quit."

ON KEY(11) GOSUB UpArrow      'Setup event handlers for key trapping.
ON KEY(12) GOSUB LeftArrow    'Keys 11-14 are the arrow keys on the
ON KEY(13) GOSUB RightArrow   'numeric keypad.
ON KEY(14) GOSUB DownArrow

KEY(11) ON   'Turn key trapping on.
KEY(12) ON
KEY(13) ON
KEY(14) ON

DO UNTIL INKEY$ = CHR$(27)   'Loop until the ESC key is pressed.
LOOP
END

'Event handlers for key traps.
UpArrow:    E = VioScrollUp (Y1, X1, Y2, X2, Lines, FillNew, Handle)
            RETURN

LeftArrow:  E = VioScrollLf (Y1, X1, Y2, X2, Lines, FillNew, Handle)
            RETURN

RightArrow: E = VioScrollRt (Y1, X1, Y2, X2, Lines, FillNew, Handle)
            RETURN

DownArrow:  E = VioScrollDn (Y1, X1, Y2, X2, Lines, FillNew, Handle)
            RETURN