Hello colinraybrown,

Monday, April 29, 2002, 9:34:45 PM, you wrote:

> --- In gbadev@y..., Phil Stroffolino <pstroffo@y...> wrote:
>> >First off, does anyone have a free fast arctan algorithm, I've
> been
>>
>> No, but if you are simply looking to steer bullets, you can just
>> normalize the deltas.
>>
>> dx = pEnemy->x - pPlayer->x;
>> dy = pEnemy->y - pPlayer->y;
>> dx = dx*dx;
>> dy = dy*dy;
>> distance = dx+dy; /* make sure to account for distance==0 */
>> dx = (dx<<8)/distance; /* #.8 fixed point */
>> dy = (dy<<8)/distance;
> yeah, this would work ok and was my first thought as well, but there
> are 2 divides which aint so cool for gba :(
You can try to convert this to one divide and two multiplications
(calculte reciprocal). This was faster on old PCs and I guess this
rule also holds for GBA. Also, if you know that your distances are
limited you can try to use look-up table and avoid division (I do it
this way in my texture-mapper, no divisions at all).

--
cheers,
-Maciej