Path: utzoo!yunexus!geac!syntron!jtsv16!uunet!lll-winken!lll-lcc!ames!mailrus!uwmcsd1!nic.MR.NET!umn-d-ub!umn-cs!mmm!ems!srcsip!mnkonar
From: mnkonar@srcsip.UUCP (Murat N. Konar)
Newsgroups: comp.sys.mac.programmer
Subject: CDEF's and Control Manager
Message-ID: <8486@srcsip.UUCP>
Date: 12 Sep 88 16:07:52 GMT
Article-I.D.: srcsip.8486
Reply-To: mnkonar@srcsip.UUCP (Murat N. Konar)
Organization: Honeywell Systems & Research Center, MPLS, MN
Lines: 64



I am trying to write a CDEF and have run into a few places where there is an
apparent inconsistency between IM's description of how 
the Control Manager interacts with CDEF's and reality. In particular:

1) When the CDEF is called with a message of drawCntl, the value of param is
supposed to be the part code of the control to draw.  The gotcha here 
(not mentioned in IM) is that the part code is in the low order word only 
so you must mask off the upper word or do something like 

thePartCode:=loWord(param)

2) The section titled "The Position Routine" (IM I-331) states that controls
that don't use the Control Manager's default method of dragging must include
a position routine. This implies that controls that DO use the default method
DO NOT need a position routine, yet when I tell the Control Manager to use the
default method (by returning zero in response to a dragCntl message), I am
still receiving a posCntl message. Infact, if there is not a position routine,
the indicator will not get updated.  Apparently, using the default method of
dragging does not exempt you from having to provide a position routine.


3) The section titled "The Thumb Routine" (I-332) says that the Thumb
Routine is only needed for controls that don't use the Control Managers 
default method of dragging the indicator.  This is contrary to what I have 
observed.  It appears that you need the Thumb Routine ESPECIALLY if you use 
the default dragging method.

And now a question:
The sequence of messages that a CDEF receives when the Control Manager is
executing the TrackControl function for a control that uses the default
method of dragging is as follows:

testCntl
thumbCntl
dragCntl
calcCRgns
posCntl      {only if start Point <> end Point}


The Control Manager uses dragGrayRgn to do the indicator dragging.  If the
start point (the point where the mouse was first pressed) is equal to the end
point (point where mouse is released), TrackControl returns zero.  If the start
and end points are different and the end point is within slopRect, TrackControl
returns the part code of the indicator.  If I choose to do my own indicator
dragging, I get the following message sequence:

testCntl
thumbCntl
dragCntl

but TrackControl returns zero no matter where I release the mouse.  How do I
tell the Control Manager what value TrackControl is supposed to return?

If anybody could answer this question or point me to an authoritative source
on writing CDEFs (I've already seen the MacTutor articles on definition
functions, they are woefully inadequate) I'd really appreciate it. 
Respond either directly or via the net.  Many thanks and a garland of 
Martian Fire Flowers in advance.

BTW, I'm doing this in Lightspeed Pascal 1.11a on a 2meg MacII running
System 5.0.
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Sorry, no disclaimer.