Square Root of -2, which would be complex. Or more commonly in shaders, square root of something just a tiny bit less than zero. Happens easily with something like:
miVector normal1, normal2;
[... fill normal 1 and normal 2 with almost identical vectors, slightly longer than 1.0 units...]
miScalar norm_diff = sqrt(1.0f - mi_vector_dot(&normal1, &normal2)); // dot product will be something like 1.000000001, resulting in square root of -0.00000001 --> not a number
which can be easily fixed by clamping the dot product to the [-1...1] range.
Ciao, Daniel!
2007/3/1, Kim Aldis <XSI(at)kim-aldis.co.uk>:
Used to have a tool that would fix single pixel anomalies. Never mind.
Sqrt( -2 ) ??
.
No, they look about 3x3. This was explained by Daniel Rind the last time this was mentioned:-
Dan wrote:-
snip
Nope, they are something like sqrt(-2) or 10/0.
And it's in the nature of the floating point specification, that whatever you do mathematically with a NAN or INF value, it will prevail. INF - 10 is still INF, and 12 * NAN is still a NAN.
So when mental ray applies it's filter kernel (which is by default a 3x3 Gauss in XSI now), then every pixel touching your NAN value will also be a NAN, which results in a black splotch that scales with your filter size.
Swarfega elegantly throws away the samples that are not a number or infinity, but ultimately you should try to find out which shader is causing them, and report / replace / fix it.
Ciao, Daniel!
snip
Kim Aldis wrote:
Is it single pixel black dots Chris?
-----Original Message-----
From: owner-xsi(at)Softimage.COM
[mailto:owner-xsi(at)Softimage.COM] On
Behalf Of Chris Marshall
Sent: 01 March 2007 15:58
To: XSI(at)Softimage.COM
Subject: Re: mmmm rounded corners
When I get a chance, I'll dig the scene out.
Daniel Rind wrote:
The lens shader is a band-aid to get rid of the symptoms, but the
problem (a
buggy shader) remains.
Ciao, Daniel!
2007/3/1, Chris Marshall <chris(at)eclipsecreative.co.uk>:
I thought you'd already identified this problem, which was why you
wrote
the swarfega lens shader?
Halfdan Ingvarsson wrote:
Do you have any example scenes that you can send me, which I can
then
forward to mental images, so that they could pinpoint the error and
fix it?
Thanks,
- ½
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