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From: tswingle@oucsace.cs.ohiou.edu (Tom Swingle)
Newsgroups: comp.lang.pascal
Subject: Microsoft mouse event handler
Keywords: mouse
Message-ID: <2929@oucsace.cs.OHIOU.EDU>
Date: 14 Feb 91 03:40:18 GMT
Sender: tswingle@oucsace.cs.OHIOU.EDU
Organization: Ohio University CS Dept., Athens
Lines: 50

I am trying to write a mouse event handler in Turbo Pascal using INT 33,
function 12 (0Ch) which gets called whenever mouse buttons are pressed.  The 
big thing I want to know is:  Do you need to declare your event handler 
procedure as an interrupt?  I have tried to do it both with and without 
declaring the procedure as an interrupt.  

Here is the program I was doing just to try it out:
 
uses crt,dos,mouse; {Mouse unit contains most common mouse functions}

var
 status,button,x,y:integer;
 regs:registers;

{$F+}
procedure leftbuttonpress; {interrupt?}

begin
 writeln('Left button was pressed!');
end;
{$F-}

begin
 minit(status,button); {Reset mouse; declared in mouse unit}
 with regs do begin
  ax:=12;
  cx:=2; {Call when left button is pressed}
  es:=seg(leftbuttonpress);
  dx:=ofs(leftbuttonpress);
 end;
 intr($33,regs);
 repeat mread(button,x,y) until button and rightdown<>0;
  { This line just waits for the right mouse button to be pressed.  Mread 
    reads the current x and y position as well as the current button status.
    Rightdown is a constant equal to 2.} 
 with regs do begin {Now turn off the event handling}
  ax:=12;
  cx:=0;
 end;
 intr($33,regs);
end.

When the procedure leftbuttonpress above is declared as an interrupt, the
message is printed on the screen but then the program hangs, but as it is now
I get a stack overflow error when it is called.  The stack overflow error makes
me think it was expecting an IRET when only a RETF was encountered, leaving the
stack a mess.  It seems to me like it should not be called as an interrupt, but
rather just as a far call.  Does anybody know which way is correct?  And why 
won't either version of my program run?  Did I mess something up in the above
program?  Thanks to anyone who can help me out.