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From: kkim@uiucdcsb.cs.uiuc.edu
Newsgroups: comp.sys.mac
Subject: Catching all keyDown events in a DA
Message-ID: <164500033@uiucdcsb>
Date: Wed, 27-May-87 12:02:00 EDT
Article-I.D.: uiucdcsb.164500033
Posted: Wed May 27 12:02:00 1987
Date-Received: Wed, 10-Jun-87 06:02:33 EDT
Lines: 72
Nf-ID: #N:uiucdcsb:164500033:000:2771
Nf-From: uiucdcsb.cs.uiuc.edu!kkim    May 27 11:02:00 1987


    I am writing a Desk Accessory which transforms every input character.
The transformation is affected by a previous character, a current char,
Caps Lock key, shift key, option key, and command key.  My DA does *not
have its own window*; it is running in the *background* and transformed 
chars will be passed to an application (e.g. MacWrite).

    My DA is working a little now.  The biggest problem is that ONLY SOME
input chars do get transformed; however, there are other input chars which
do not get transformed.  I will show you a skeleton of my DA in Lightspeed
Pascal to give you a concrete idea.

-----------------------------------------------------------------
procedure OpenRoutine;
begin
    dCtlStorage:=NewHandle(SizeOf(PrivateStorage));
    dCtlFlags:=$6400; {DA can respond to control calls;}
        {DA needs time for performing periodic actions;}
        {DA will be locked in memory as soon as it is opened}
    dCtlDelay:=0; {must be called as often as possible}
    dCtlEMask:=keyDownMask;{meaningless?}
    whenSaved:=0;{evtQWhen of the latest keyDown event processed by a DA}
end;

procedure ControlRoutine;
begin
for counter:=1 to LIMIT do begin {LIMIT will be explained below}
    evQHdrPtr:=GetEvQHdr; {get a pointer to the header of the event queue}
    CurrElem:=evQHdrPtr^.qHead;
    while (CurrElem <> nil) do
        if (CurrElem^.evQElem.evtQWhen > whenSaved) then begin
            {an event which has not been processed by a DA; do transformation}
            CurrElem^.evQElem.evtQMessage:=transformedChar;
            whenSaved:=CurrElem^.evQElem.evtQWhen;
            end; {if}
        end; {while}
    end; {for counter}
end;

procedure CloseRoutine;
begin
    disposHandle(dCtlStorage);
end;

---------------------------------------------------------------
    I test my DA using MacWrite.  At first, LIMIT was 1 (i.e. no for loop).
The result was that about 2/3 of input chars did not get transformed.
The following table will help:

LIMIT            portion of input chars which did not get transformed
  1              2/3
 10              1/2
700              1/10
1000             1/15
2000             < 1/30

    When LIMIT was greater than about 500, some characters were lost if
I typed fast (due to the maximum event queue size).  I guess that LIMIT
shoud be set to 1 and some other mechanism must be adopted to get around
the problem. Does Vertical Retrace Manager have anything to do with it?


    Could anybody give me clues/hints/comments as to how to CATCH ALL THE 
KEYDOWN EVENTS IN A DESK ACCESSORY AND TRANSFORM THEM?

    Thanks in advance.

Kyongsok KIM

Dept. of Computer Science; Univ. of Illinois at Urbana-Champaign
arpanet/csnet: kkim@a.cs.uiuc.edu
usenet/uucp  : {seismo, pur-ee, ihnp4}!uiucdcs!kkim