RE: mmmm rounded corners

["Kim Aldis" <XSI(at)kim-aldis.co.uk>]

Sorry, I misread the mail.

 

From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of Daniel Rind
Sent: 02 March 2007 00:24
To: XSI(at)Softimage.COM
Subject: Re: mmmm rounded corners

 

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 ) ??

 

.

From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf Of Chris Marshall
Sent: 01 March 2007 16:42

To: XSI(at)Softimage.COM
Subject: Re: mmmm rounded corners

 

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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