Keyboard Unit

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{=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
=-=-=-=-=-=-                                                     -=-=-=-=-=-=
-=-=-=                     Keyboard Interface Unit                     =-=-=-
=-=-                                                                     -=-=
-=-=-=                     Coded by: Chris Lattner                     -=-=-=
=-=-=-=-=-=-                        1995                         -=-=-=-=-=-=
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=}
UNIT Keyboard;
INTERFACE
USES DOS;

CONST                   { Commonly used scan codes }
  ScEsc        = 1;
  ScUp         = 72;
  ScLeft       = 75;
  ScRight      = 77;
  ScDown       = 80;

VAR
  Keys : ARRAY[0..255] OF BOOLEAN;

(*  Example program - Here is a program that demonstrates the commonly used
  functions available in this unit:

  VAR
    X, Y : INTEGER;
  BEGIN
    InstallKBHandler(False);

    WHILE NOT Keys[ScESC] DO
    BEGIN
      IF Keys[ScUp   ] THEN DEC(Y);
      IF Keys[ScDown ] THEN INC(Y);
      IF Keys[ScLeft ] THEN DEC(X);
      IF Keys[ScRight] THEN INC(X);
      DrawFrame(X, Y);
    END;
    RemoveKBHandler;
  END.                                                                    *)

PROCEDURE InstallKBHandler(CallBios : BOOLEAN);
(*  InstallKBHandler - Installs a low level keyboard handler that can handle
  multiple keys down.  If the "CallBios" parameter is TRUE then the Bios and
  DOS functions can be used to access the keyboard.  READLN, READKEY and the
  like will work.   This is slower, and you will get an annoying beep if the
  BIOS's buffer gets full.   I recommend only using this mode when debuging.

    The other mode of operation is activated when  "CallBios" is FALSE.  The
  BIOS's handler doesn't get called.   It is a faster and more versitile way
  of  accessing the  keyboard.   Whenever a key is pressed, the  replacement
  handler calculates the scancode and sets in the element in the "Keys" with
  the corresponding number.  When it is released, it clears the element. The
  main problem with  this mode is when debuging.   CTRL-Break is ignored, so
  debugging becomes  more of a problem.   Because of this, I often  use this
  statement when I first initialize the keyboard:

     InstallKBHandler({$IFDEF Debug THEN} TRUE {$ELSE} FALSE {$ENDIF});

  In the main loop of your program, call "ClearBiosKbBuffer"  and all of the
  annoying beeps will be stopped.                                         *)

PROCEDURE RemoveKBHandler;
(*  RemoveKBHandler - Removes the low level keyboard handler.  MUST be
  called if the handler is installed.  (The keyboard would be in-operable
  after the main program terminates if the custom handler is not removed) *)

PROCEDURE ClearBiosKbBuffer;
(*  ClearBiosKbBuffer - Has the effect of the following statement:

                WHILE NOT Keypressed DO ReadKey;

  But of course, it is much faster and simpler.                           *)