Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!snorkelwacker!usc!cs.utexas.edu!mailrus!cornell!biar!trebor
From: trebor@biar.UUCP (Robert J Woodhead)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Line selection algorithims..
Message-ID: <981@biar.UUCP>
Date: 16 Dec 89 19:15:02 GMT
References: <8912160053.AA00720@cadman.nyu.edu>
Organization: Biar Games, Inc.
Lines: 31

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.

2) When a mouseDown occurs, we can check the position against the
rectangles for the objects, in order of the object's frontness.

3) If this matches, we then go into a special checking routine, one
for each object type, that does any special checks needed to determine
if there is really a hit.

The most obvious optimization is to note that objects not in display
cannot be clicked on; thus anytime we scroll the window, generate a
list of all the objects that intersect it (easy to do since we have
to find them to display them) - then on clicks we only have to search
this subset.

-- 
Robert J Woodhead, Biar Games, Inc.   !uunet!biar!trebor | trebor@biar.UUCP
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