Re: [Algorithms] Rounding Problem

[Paul at H. <pa...@ru...>]

Apparently not, that's where I came in. I'm actually starting to think there 
could be a bug elsewhere but this scenario is a nightmare for trying to 
actually trace into stuff and spot when the problem happens.

It might be that my grid coordinates are not overlapping perfectly and I'm 
reading the wrong bit of map ? Because of the negative, they were out 
somewhat before I added the floors there.

Regards,
Paul Johnson.
www.rubicondev.com


----- Original Message ----- 
From: "Megan Fox" <sha...@gm...>
To: "Game Development Algorithms" <gda...@li...>
Sent: Tuesday, May 20, 2008 6:16 PM
Subject: Re: [Algorithms] Rounding Problem


> float val = (coord + 15.5) / (15.5 * 2.0) * 31.0;
> float gridAmt = val - (int)val;
>
> ... which in this case simplifies out to just coord + 15.5, but you
> get the idea.  Or at least I think that works out right?
>
> On Tue, May 20, 2008 at 11:01 AM, Paul at Home <pa...@ru...> 
> wrote:
>> God this is driving me nuts. It should be so simple!
>>
>> I have a world system whereby a grid of 31x31 in grid units is mapped 
>> over a
>> range of real values ranging from -15.5 to +15.5
>>
>> For collision detection reasons, I need a function that will basically do 
>> a
>> mod such that when applied to my real X or Z coordinate, it tells me (as 
>> a
>> range 0-1) how far into a grid cell I am. I would expect the routine to
>> return 0.1 if I'm a tenth into a particular grid square.
>>
>> But, whatever combinations of mod,floor,ceil,etc I've tried, when the 
>> real
>> coord is negative, I get a 0.9 instead of a 0.1
>>
>> I'm kinda looking for a float version of "&" iyswim.
>>
>> Any ideas what I'm doing wrong ?
>> ==========================================
>> RoundDown=crt floorf btw
>>
>> tINT GetGridXFromWorld (tF32 WorldX)
>> {
>> return tINT(RoundDown(WorldX+15.5F));
>> }
>> tINT GetGridYFromWorld (tF32 WorldZ)
>> {
>> return tINT(RoundDown(15.5f-WorldZ));
>> }
>>
>> I would expect this function to return how far into the current square I 
>> am
>> as a normalised "percentage". It's changed a lot but this is definitely
>> wrong. I just can't seem to fix it!
>> tF32 Frac=Abs((Zc+0.5F)-RoundDown(Zc+0.5F));
>>
>>
>> Regards,
>> Paul Johnson.
>> www.rubicondev.com
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>
>
>
> -- 
> Megan Fox
> Idyllon, LLC
> http://www.shalinor.com/
> http://www.idyllon.com/
>
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