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From: schwager@m.cs.uiuc.edu (Michael Schwager)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: Clicking on irregular shapes?
Message-ID: <1991Mar28.234604.22793@m.cs.uiuc.edu>
Date: 28 Mar 91 23:46:04 GMT
References: <1991Mar27.212214.6204@orfeo.radig.de>
Organization: University of Illinois, Dept. of Comp. Sci., Urbana, IL
Lines: 40

eric@orfeo.radig.de (Eric Tuerlings) writes:
>I can remember there was a discussion last year about: "Clicking on
>irregualar shapes". Because I want to use irregular shapes to click on,
>I am interested in a solution to this problem, since I found nothing else
>than to click on rectangle shapes only.

>Does somebody know a solution?
>-- 
>Eric Tuerlings,					 E-Mail:  eric@radig.de

Hi,
I was the one who asked the question.  I'll try to describe what I did:

I have a map of the world, that looks remarkably like a Risk board :-).  I
made it using DPaint.  I saved each territory as a seperate brush.  Then I
used iff2c on each of those files, and got a lovely 1-bitplane description
of the shape (if your shapes are >1 bitplanes deep, I suggest converting
them to only a single color before saving them, so iff2c creates a single
bitplane representation of the shape... a "cookie").  It was kind of a
tedious process: first I cleaned up all around the image, then I used the
grab brush tool (grabbing a rectangular area and noting the upper left
coordinates of the object), then I saved this brush, and finally used iff2c
on it.  iff2c will give you the width and height of your object (in an
Image structure).  So now I have this file that I saved all these image
structures in....

This is known as the "cookie-cutter" technique.  Thanks to someone from
Commodore for describing it to me.  It's yecksellent having Commodore Tech
people on the Net!

On the screen, let's say I click at x=400, y=100.  My algorithm goes
thusly:  1. Which rectangles (captured above) contain that point?  2. Of
those rectangles, which one has a 1 bit in the position in question (there
can be one and only one)?  3. Bingo!  I have found an object! 

I decided to use this technique because once I've clicked on an object I
wanted it to flash, by xor'ing the cookie's bitmap with the proper location
and planes in the screen's bitmap.  So I knew I was gonna have to make the
cookies anyway.
-Mike Schwager