From:	Arno Fehm <afehm AT bigfoot DOT de>
Newsgroups:	comp.games.development.programming.algorithms,comp.os.msdos.djgpp
Subject:	Re: Calculating direction to shoot in
Date:	Sat, 01 May 1999 18:23:07 +0200
Organization:	Regionales Rechenzentrum Erlangen, Germany
Message-ID:	<372B2A6B.E0D572D9@bigfoot.de>
References:	<372AFE6B DOT D048BBCE AT webmail DOT co DOT za>
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To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp
Reply-To:	djgpp AT delorie DOT com

Hi you!

Ebola wrote:
> How do I calculate the direction/angle the computer controlled 
> enemies have to shoot in to hit the player? For example: 
> The player is at coordinates (101, 254) and the
> enemy is at (235, 456). How can I calculate the angle between them?
Well, two points do not really have an 'angle' (you need 3)!!! What you
probably want is the angle in relation to the x-axis.
             
Then it's simple vector subtraction! ( let a be the angle )

         101           235                 -134
 Player        - Enemy       =  direction
         254           456                 -202

Trigonometry tells us (sqrt(x) is the square root of x):

 sin a  =  ( -202 ) / sqrt( (-134)² + (-202)² ) => a = -56°
 cos a  =  ( -134 ) / sqrt( (-134)² + (-202)² )

You probably have to pay to attention if you have to add something like
180° or not!


Hope, this helps you a bit!
-- 
Arno Fehm (afehm AT bigfoot DOT de)

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