Path: chuka.playstation.co.uk!news
From: James Chow <james@chowfam.demon.co.uk>
Newsgroups: scee.yaroze.beginners
Subject: Re: sin and cos
Date: Thu, 22 Jul 1999 06:59:28 +0100
Organization: PlayStation Net Yaroze (SCEE)
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Look up tables are much faster (I've not done any proper timings -
but I reckon in the region of 100 times faster...)
Sin/cos functions in the libraries uses radians and not degrees.
360 degrees = 2 * PI radians
1 degree = (2 * PI / 360)  radians
Sorry, don't know about the >> 12 tho, haven't looked at the code.
I know using >> bit shift operator is a trick to do quick division on
integers by numbers to the powers of 2. so >> 12 does x / (2^12)
ie x/4096. The rotate member variable in GsSPRITE uses 4096
units for 1 degree which is probably the reason for >> 12.

#define PI         (3.14159265)
double SIN[360];
double COS[360];

//initialise look up tables before using
for (i=0; i<360; i++)
{
  SIN[i] = sin(2 * PI * i / 360);
  COS[i] = cos(2* PI * i / 360);
}

//to get sin/cos values
int degree = ?;
degree = degree % 360;  //restrict to +/- 360
if (degree < 0)
  degree = degree + 360;   //if negative, make positive
int sindegree = SIN[degree];
int cosdegree = COS[degree];

Sorry if this isn't very clean, but I'm writing this on the fly.
Cheers.
James.


Eddie Harrison wrote:

> Does any 1 now how to use sin or cos in a game at the moment i am using
> a bit of code i have borrowed which involves look up tables and i don't
> understand it ( it from amatuer wars and uses a >>12 thing in it ) . i
> have also looked at the section in the libary reference but like the
> rest of the book it means nothing to me . if anyone know's which is
> faster look up tables or the sin function please tell me .
> here is my attempt so far at using lookup tables
>
> #include <libps.h>
> #include "sincos.h"
>
> int main()
> {
>
> int adjacent,oppisate,angle;
>
> angle = 32;
>
> adjacent = (SIN[angle]*10);
> oppisate = (COS[angle]*10);
>
> printf("A triangle has a angle of %d\n",angle);
> printf("and a hypotonuse of 10 so!!\n");
> printf("so it's adjacent side is %d long\n",adjacent);
> printf("and its oppisate side is %d long\n\n",oppisate);
>
> return 0;
> }