PEN Statements


 Example

 See the  ON PEN statement programming example, which uses the  PEN function.


 PEN Statements
 ----------------------------------------------------------------------------


 Action

 Enable, disable, or suspend lightpen-event trapping.


 Syntax


  PEN ON

  PEN OFF

  PEN STOP

 Remarks


 The  PEN ON statement enables lightpen-event trapping. A lightpen event
 occurs whenever the lightpen is activated by pressing the tip to the screen
 or pressing the touch ring. If a lightpen event occurs after a  PEN  ON
 statement, the routine specified in the  ON  PEN statement is executed.

 The  PEN OFF statement disables lightpen-event trapping. No trapping takes
 place until a  PEN  ON statement is executed. Events occurring while
 trapping is off are ignored.

 The  PEN  STOP statement suspends lightpen-event trapping. No trapping takes
 place until a  PEN  ON statement is executed. Events occurring while
 trapping is suspended are remembered and processed when the next  PEN  ON
 statement is executed. However, remembered events are lost if  PEN  OFF is
 executed.

 When a lightpen-event trap occurs (that is, the  GOSUB is performed), an
 automatic  PEN STOP is executed so that recursive traps cannot take place.
 The  RETURN statement from the trapping routine automatically performs a
 PEN ON statement unless an explicit  PEN OFF was performed inside the
 routine.

 A  PEN ON statement must be executed before you use the  PEN function. If a
 Pen function is executed when the lightpen is off, BASIC generates the error
 message Illegal function call.


 Note

 The lightpen requires an IBM Color Graphics Adapter.

 The  PEN statements are not available for OS-2 protected mode.

 For more information, see Chapter 9, "Event Handling" in the  Programmer's
 Guide.


 See Also

  ON  event


 Example


 The following example uses the  PEN statements and the  PEN function to
 enable and display current lightpen status (up or down) and position (x and
 y coordinates). The  ON PEN statement passes control to the PenReport
 routine when a lightpen event occurs.

 ' Note. Do not run this program with your mouse driver enabled.
 CLS                ' Clear screen.
 COLOR 0, 7         ' Set black on white.
 CLS                ' Clear screen.
 PEN ON             ' Enable lightpen
 ON PEN GOSUB PenReport
 DO
     LOCATE 23, 12
     PRINT "Press the lightpen against the screen to see a report."
     LOCATE 24, 17
     PRINT "  Press the Spacebar to exit the program.     ";
 LOOP UNTIL INKEY$ = " "
 PEN OFF            ' Disable lightpen.
 COLOR 7, 0         ' Set back to black on white.
 CLS                ' Clean up the screen.
 END

 PenReport.
     DO
         P = PEN(3)
         ' Report lightpen status and get X and Y position.
         LOCATE 10, 27
         PRINT "A Pen event has occurred."
         LOCATE 24, 17
         PRINT "Press ANY key to exit the lightpen report.";
         LOCATE 12, 30
         PRINT "lightpen is ";
         IF P THEN
             PRINT "Down"
             X = PEN(4). Y = PEN(5)
         ELSE
             PRINT "Up  "
             X = 0. Y = 0
         END IF
         ' Report the X and Y position.
         LOCATE 14, 22
         PRINT "X Position ="; X; "   "
         LOCATE 14, 40
         PRINT "Y Position ="; Y; "   "
     LOOP WHILE INKEY$ = ""
     RETURN