Path: chuka.playstation.co.uk!news
From: "John \( QuietBloke \)" <quietbloke@btinternet.com>
Newsgroups: scee.yaroze.freetalk.english
Subject: Re: Daft Question
Date: Mon, 20 Aug 2001 21:09:16 +0100
Organization: PlayStation Net Yaroze (SCEE)
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Hi Pal,

I had a good think about this today ( Im afraid a barbeque kinda got me too
mashed up to do anything yesterday ) and your solution seems to fit exactly
what I thought Id have to end up doing ( ie some sort of lookup table ) as
the maths functions arnt exactly speedy on the PSX. I was kinda hoping there
was a wierd and wonderful way of getting this done using the matrices or
something.
As it seems you have done all the hard work and come up with a solution Id
be very grateful if you could pass it on to me.. it'll save me a lot of
time. I was just about to sit down and try to figure it out.. as if progress
on the game isnt slow enough already.

Of course Matt and now Omar arnt helping matters by eating onto my spare
time <grin>.. not that Im complaining :)

Cheers
John ( QuietBloke )



"pal" <pal_news@hotmail.com> wrote in message
news:01c1297e$8cb6e8a0$LocalHost@pal-s-omnibook...
> 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
>