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Hair revisited

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I remember Jim mentioning something about lights when he had a similar problem. I can't find the thread though, I think it was on SESI's forum.

Perhaps move your lights further away from the object and see if it helps?

Aye. As it turns out moving the lights only really helped in that scene. I never really figured out why those burnouts occur. I suspect at certain angles the model freaks out. At one point I got pretty close to narrowing down which term was the culprit but then 'work' reared its ugly head and I haven't had time to go back to it. <_<

(I'm secretly waiting for a job to come in that requires hair so I* can look into this again.)

* When I say, "I", I really mean Mario. ;)

Edited by Wolfwood

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I'm not entirely sure you'll get better than spice's shader. Especially not from SESI... no offense, but shaders aren't their strong point :).

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I'm not entirely sure you'll get better than spice's shader. Especially not from SESI... no offense, but shaders aren't their strong point :).

yeah i guess u'r right, but it would be nice if they could get a shader like spice's and make it work properly!!

jason

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yeah i guess u'r right, but it would be nice if they could get a shader like spice's and make it work properly!!

Just for the record, I'm not sure what causes those burn outs. I might be something as simple as a bug in the shader, or a implementation oversight. It could even be a issue with the model itself and Arno (spice) could have implemented it perfectly. It also possible that those hotspots are correct but since model doesn't support multiple scattering the illumination isn't being spread around.

Maybe its time to go back and take another look. Fresh eyes might provide some insight. :)

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Just for the record, I'm not sure what causes those burn outs. I might be something as simple as a bug in the shader, or a implementation oversight. It could even be a issue with the model itself and Arno (spice) could have implemented it perfectly. It also possible that those hotspots are correct but since model doesn't support multiple scattering the illumination isn't being spread around.

Maybe its time to go back and take another look. Fresh eyes might provide some insight. :)

def seems sensitive to light/camera angles, i've been playing around with it using fur, i'm still getting burnouts

jason

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Hi All,

it sems that those bright spots are a consequence of the limited floating point accuracy of Mantra. However, I'll try to fix this issue. Hence, it would be great to have a simple test scene (with artifacts).

Ciao,

Arno

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Hi All,

it sems that those bright spots are a consequence of the limited floating point accuracy of Mantra. However, I'll try to fix this issue. Hence, it would be great to have a simple test scene (with artifacts).

Ciao,

Arno

This is a simple scene with a light rotating around a NURBS tube. (Frame 130 seems to have a burn out.)

Since most of the lighting calculations take place in a polar space(?) is it possible something is blowing up due to x/0?

arno.hip

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This is a simple scene with a light rotating around a NURBS tube. (Frame 130 seems to have a burn out.)

Since most of the lighting calculations take place in a polar space(?) is it possible something is blowing up due to x/0?

Thanks.

No, this is not an "x/0" issue. :-)

-Arno

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No, this is not an "x/0" issue. :-)

That's too bad, those are easy to fix. ;)

Thanks a ton for looking into this.

:D

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Hi All,

Here is a modified version of my shader (for hair with a circular cross section) which hopefully fixes the "bright spot" issue. It would be great if you could perform some tests to see if it works properly.

Ciao,

Arno

[EDIT: Please reload this version !]

arno_hair_far_field_v_1_9.zip

Edited by spice

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so far so good, i'm setting up a render for the weekend, lets se how it comes out!

thx spice

jason

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Thanks for all your work Arno, it's much appreciated :)

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I just took an old sample and applied the new shader. Seems to work nicely.

Thanks for testing ! I would really appreciate to see some results obtained with the shader. :-)

-Arno

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hey

i just noticed that the hair shader isn't using deep shadows? it creates shadows on another surface, but it doesn't seem to self shadow.

any ideas?

check out the images below:

thx

j

post-1653-1179846021_thumb.jpg

post-1653-1179846045_thumb.jpg

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hey

i just noticed that the hair shader isn't using deep shadows? it creates shadows on another surface, but it doesn't seem to self shadow.

any ideas?

check out the images below:

thx

j

I will check that tomorrow...

-Arno

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I will check that tomorrow...

-Arno

Odds are you just need something like

illuminance(P,N,PI_2) {
	shadow(Cl);
	// ...
	// Bunch of awesome stuff
	// ..
	Out = Cl;
}

Edited by Wolfwood

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Odds are you just need something like

illuminance(P,N,PI_2) {
	shadow(Cl);
	// ...
	// Bunch of awesome stuff
	// ..
	Out = Cl;
}

Thanks.

Here is a version including the shadow call in the illuminance loop....

-Arno

arno_hair_far_field_v_1_9_shadow.zip

Edited by spice

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