From: cs19 AT cityscape DOT co DOT uk (BDC Client Team)
Newsgroups: comp.os.msdos.djgpp
Subject: Help with bit-masking Allegro sprites
Date: Thu, 17 Jul 1997 12:20:33 GMT
Organization: IP-GOLD User
Message-ID: <869142033.25228.0.nnrp-5.9e9829a4@news.demon.co.uk>
NNTP-Posting-Host: itsb.demon.co.uk
Lines: 21
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Precedence: bulk

Hi all,

I have been working on a routine for a pixel-perfect collision detection
for Allegro sprites.  The basic idea is that you create a bit-mask
for each Allegro sprite, do general bounding-box detection until
this flags a collision and then use the bit-masks to see if a *true* 
collision has occured (i.e. actual pixels overlap).

I'm fairly sure that I am creating the bit-masks correctly, but when I come
to (logically) 'and' two bit-masks together I get false returns all the time.
I have gone through my code time and again, and just can't spot where I
am going wrong.

Would anyone out there be prepare to look at the code (it's only 300 lines long)
and point me in the right direction?

Thanks in advance


Neil Chinnery
http://www.geocities.com/SiliconValley/Park/1077