Path: chuka.playstation.co.uk!news
From: "pal" <pal_news@hotmail.com>
Newsgroups: scee.yaroze.freetalk.english
Subject: Re: Daft Question
Date: 20 Aug 2001 14:03:46 GMT
Organization: PlayStation Net Yaroze (SCEE)
Lines: 25
Message-ID: <01c1297e$8cb6e8a0$LocalHost@pal-s-omnibook>
References: <9loc6a$p3k2@www.netyaroze-europe.com> <9loeu8$p3k3@www.netyaroze-europe.com>
NNTP-Posting-Host: nas-cbv-6-11-21.dial.proxad.net
X-Newsreader: Microsoft Internet News 4.70.1155

Coincidence... I just implemented that in Invs yesterday! After a bit of
research, here is what I finally found out:

Use atan2. It's designed for that.
angleInPslibDegrees = (4096 * 180/PI) * atan2(x2 - x1, y1 - y2)
with PI ~= 3.141592

- beware of the inverted y axis (on the screen it goes downwards while in
math it usually goes upwards).

- beware of the direction of the original sprite. This formula works with
the original sprite pointing up (I'm not sure why).

- if x2 == x1 and y2 == y1 can happen, be sure to remember and keep the
angle before that step, as these values are not allowed (you'd get zero,
which is normally not what you want).

- as the whole calculus (including conversion to pslib degrees) ends up
being far too long, I recommend using a precalculated table. I wrote a
precalculator for Invs; let me know if you want to have a look at it.


Hope this helps,
pal