Gordon wrote:
> 
> Hi All,
> 
> I got this the other day and after bashing on my code for a couple of hours
> found that it was what appears to be a POVRay bug.
> 
> I have a file that uses the clock value for animation. I set the animation
> to use 10 frames. I multiply clock by 4 for my animation. I then take
> modulus 1.0 to get the fractional part of the number only. The problem is
> that at frame 5 the value is 1.0 (ie Y=mod(clock*4,1.0); results in Y=1.0).
> Now when I did maths, mod(x,1.0) can NEVER be equal to 1.0, what gives?
> 
> After some investigation, I found that the value for the clock at frame 5 is
> around 2.00000000000000001! This still doesn't explain how the mod()
> function gives me 1.0 as an answer though, so perhaps there are two bugs
> here, one in the calculation of clock values, and one in the mod function.
> 
> Has anyone else seen this? Does anyone have a way to work around this error
> that will work regarless of the number of frames? ( If I use an odd number
> of frames, the problem goes away )

I found the same problem with imprecision in the clock variable while
working on my latest IRTC entry; it was causing things to happen a
frame late.  I put the following code at the beginning:

#declare Frame=floor(clock*24+.001); // 24 frames per second animation
#declare Clock=Frame/24; // get actual clock value

I then use the Clock label instead of clock.

Regards,
John

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