Path: chuka.playstation.co.uk!news
From: "Rad" <rad@cyberdude.com>
Newsgroups: scee.yaroze.programming.2d_graphics
Subject: Re: What do'you mean I have to brush up on me maths!
Date: Sun, 11 Jul 1999 17:36:02 +0100
Organization: PlayStation Net Yaroze (SCEE)
Lines: 67
Message-ID: <7mah71$t1v6@chuka.playstation.co.uk>
References: <7ko1jf$33u25@chuka.playstation.co.uk> <376fbd21.251404588@news.scea.sony.com> <7lkucs$ko217@chuka.playstation.co.uk> <7lnteg$i9a1@chuka.playstation.co.uk> <37823145.682258342@news.scea.sony.com>
NNTP-Posting-Host: modem-195.name53.dialup.pol.co.uk
X-Newsreader: Microsoft Outlook Express 4.72.3110.5
X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3

Thanks for the help guys.

Right, next question :)

I want to move something in a continuous sound wave frequency type pattern,
does anybody know if I can do that with a maths formula?

Thanks,

Rad.
rad@cyberdude.com
http://www.netyaroze-europe.com/~radpsx

p.s. Scott - did you find out which method (sqrt or inv_tan) was faster? Oh
and why can't you just use a simple look-up table for inv_tan?


Scott Cartier wrote in message <37823145.682258342@news.scea.sony.com>...
>>Hi Rad,
>>
>>First find the distance between the two objects:
>>
>>    dx = x1 - x2
>>    dy = y1 - y2
>>
>>Next find the length of the line between the two objects:
>>
>>    dxy = square_root( dx*dx + dy*dy )
>>
>>And now the vector:
>>
>>    vx = (dx * speed) / dxy
>>    vy = (dy * speed) / dxy
>>
>>
>>I think that'll do the trick.  Due to the integer maths, there will be
>>accuracy problems if the speed is low, or if the two objects are very
close,
>>but this can be fixed by using fixed point if necessary.
>>
>>Herbs
>
>
>You can avoid the squareroot by doing an inverse tangent instead.
>Whether this is faster or not I'm not sure.  First, find dx & dy like
>above.  Then find the angle of this line:
>
>  Angle = inverse_tan(dy / dx)
>
>Once you have the angle you can get the vx & vy components using sin
>and cos:
>
>  vx = cos(angle)
>  vy = sin(angle)
>
>I hope I didn't get those switched.
>
>Use a look-up table for the tan, sin, and cos to speed things up.  The
>inverse tangent takes a bit longer despite using a look-up table.
>This may or may not actually be faster than doing the sqrt() as Alex
>suggests.  That would be an interesting experiment (and one I probably
>should have performed before blindly going with the inverse tan
>method).
>
>Scott