NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/comp/sys/mac/programm/20972

Internet Message Format | 1993-01-08 | 2.1 KB

Path: sparky!uunet!gatech!darwin.sura.net!zaphod.mps.ohio-state.edu!malgudi.oar.net!hyperion!desire.wright.edu!jmatthews
From: [e-mail]
Newsgroups: comp.sys.mac.programmer
Subject: Detecting double click?
Message-ID: <[e-mail]>
Date: 8 Jan 93 00:28:31 EST
Organization:  Wright State University
Lines: 52

Recently I suggested the following way to check for double clicks:

 var gLastMouseUp: EventRecord;

 procedure SaveLastMouseUp(event: EventRecord);
 begin
   gLastMouseUp := event
 end;

 function CheckDoubleClick (event: EventRecord): Boolean;
   var slop: Rect;
 begin
   with gLastMouseUp.where do
     SetRect(slop, h - 2, v - 2, h + 2, v + 2);
   CheckDoubleClick:= ((event.when - gLastMouseUp.when) <=
     GetDblTime) and (PtInRect(event.where, slop))
 end;

In the main event loop, call SaveLastMouseUp in response to mouseUp
events, and call CheckDoubleClick in response to mouseDown events. The
latter returns true when a double click (as defined in IM vol.I,
p.260) occurs.

This definition of a double click can lead to some confusion in
subsequent calls to StillDown or WaitMouseUp. An alternative is to
measure time between mouseDown events as follows:

 var gLastMouseDown: EventRecord;
 {should initialize gLastMouseDown.when to 0}

 function CheckDoubleClick (event: EventRecord): Boolean;
   var
     slop: Rect;
     test: Boolean;
 begin
   with gLastMouseDown.where do
     SetRect(slop, h - 2, v - 2, h + 2, v + 2);
   test := ((event.when - gLastMouseDown.when) <= GetDblTime) and
            (PtInRect(event.where, slop));
   if test then
     gLastMouseDown.when := 0 {prevent multiple clicks}
   else
     gLastMouseDown := event; {save this one for future testing}
   CheckDoubleClick := test
 end;

How are others doing it?

o----------------------------------------------------------------------------o
| John B. Matthews, [e-mail], disclaimer:= myViews <> WSU |
|      "Whom the gods would destroy, they first invite to program in C"      |
o----------------------------------------------------------------------------o