Path: utzoo!attcan!uunet!cs.utexas.edu!usc!apple!Apple.COM!lsr
From: lsr@Apple.COM (Larry Rosenstein)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Line selection algorithims..
Message-ID: <5835@internal.Apple.COM>
Date: 18 Dec 89 21:18:01 GMT
Sender: usenet@Apple.COM
Organization: Objects-R-Us,  Apple Computer, Inc.
Lines: 26
References:<8912160053.AA00720@cadman.nyu.edu> <1989Dec17.104221.23095@santra.uucp>

In article <1989Dec17.104221.23095@santra.uucp> jmunkki@kampi.hut.fi (Juri 
Munkki) writes:

> grafport with a single pixel (or many pixels, if your pointer should
> not be with single pixel resolution). Then draw all objects with a
> black penpat.
> 
> You have to draw the objects from front to back. I also recommend that

You can draw the shapes back to front (the way you would draw them on the 
screen) and select the last one that touched the pixel.

The advantage of this algorithm is that is works for any shape regardless 
of how complex it is.  If you need to compute the distance to the shape 
then you need a different formula for lines, ovals, etc.
 
> This algorithm is surprisingly fast. I guess QuickDraw clips so well

I implemented this in a MacApp graphics building block, and it works very 
well.

Larry Rosenstein, Apple Computer, Inc.
Object Specialist

Internet: lsr@Apple.com   UUCP: {nsc, sun}!apple!lsr
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