Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!tut.cis.ohio-state.edu!cica!iuvax!maytag!aries5!jb
From: jb@aries5.uucp (James Bruyn)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Line selection algorithims..
Message-ID: <1043@maytag.waterloo.edu>
Date: 18 Dec 89 01:50:00 GMT
References: <8912160053.AA00720@cadman.nyu.edu> <981@biar.UUCP>
Sender: daemon@maytag.waterloo.edu
Reply-To: jb@aries5.UUCP (James Bruyn)
Organization: Computer Systems Group, University of Waterloo
Lines: 30

In article <981@biar.UUCP> trebor@biar.UUCP (Robert J Woodhead) writes:
>deragon@CADMAN.NYU.EDU (John Deragon) writes:
>
>>		I was wondering how the current applications like
>>MacDraw, MacDraft...etc etc do the line selection. For example in 
>>MacDraw you click on the line and it becomes selected? How does it 
>>do this? What is it testing on mouseDown? 
>
>I don't know how THEY do it, but at first thought, the way I would do
>it is as follows:
>
>1) Note that every object has an associated rectangle that contains
>it.
>
That was my immediate thought to - gee how simple.  But then I realized
that a line could be on a diagonal, and the enclosing rectangle would
then be quite large.  So I think a more reasonable way would be
to define a region around the line with some room for slop. i.e.
assuming the line goes from lower left to upper right. 
(left.h-3,left.v-3;,
 right.h+3, right.h-3;
 right.h+3, right.v+3;
 left.h+3, left.v+3;
 left.h+3, left.v-3) 
and then checking whether the mouse in local coordinates is within the
region.

Jim Bruyn
Computer Systems Group
University of Waterloo.