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 Post subject: Re: Kristinka Hair Tests
PostPosted: 25 Apr 2010, 18:05 
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Well done, Anto!

Sorry everyone for the lack of updates (and the tutorial) . . Need to get back on track.

Here's a scene file for the last picture I posted (SI '11 format)

Btw: Did anyone notice improved render times when using ray tracing with strand hair in SI 2011? By some first tests, it seems to be faster than rasterizer now compared to SI 2010. Might be some glitch in my setup also.

Btw Anto, AbsoluteShapeWidth seems to change the look of the render also, I can't get it to look the same as when rendering with Pixel Units. It looks a bit more like wires than hair.
Attachment:
File comment: Test: two pointclouds with diff. hairstyles merged
IMG_H1.jpg
IMG_H1.jpg [ 85.42 KiB | Viewed 3284 times ]

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 Post subject: Re: Kristinka Hair Tests
PostPosted: 08 May 2010, 22:20 
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Hi,

here is a small experiment with final gathering and ICE strands. For ICE strands, I think it's good idea to always use 'Long Hair' diffuse model in Hair Renderer -
not only because long hair is modeled. Even with short hair, info about normals from emitter's surface doesn't exist (at least I think so). Also, Kristinka Hair nodes does not respect old fashion hair shading rule of 'first segment parallel to emitter's normal'.

So, 'Long hair' diffuse model calculates shading normals relative to direction to lights - but in case of final gathering, what normals are used ? I'm still not sure, to be honest. For this experiment, I've used only one light with very low intensity, didn't noticed any influence of this one to FG shading.

Fortunately, we can provide a custom shading normals to Hair Renderer. Custom vector is used as an input for 'normal' in Bump Generator node, as well 'Relative to Input Normal' option with node. 'Bump Factor' is set to zero, as we already can't use bitmap, there is no 2d mapping with hairs, only normals are important here. To get it work, 'Normal Blend' in Hair Renderer need to be at more than zero.

Now, examples. Two at bottom are Eye Ray Vector - normal are looking at camera, or inverse. Second one looks most promising to me, it's custom attribute already created by kH Follow NURBS styling modifier - this is in fact, surface normal of NURBS surface used for styling, sampled for each strand segment of hair guides, then transferred to rendered strands/hairs. This is fast setup, of course it's possible to create a more fancy solution, with complex setups.

Cheers

Image

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 Post subject: Re: Kristinka Hair Tests
PostPosted: 09 May 2010, 01:44 
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Interesting, it never occured to me that this is even a problem before xD

Wouldn't the best normals for fg be:
(walking along the width of a strand) ...
cross product of inverse eye ray and strand segment's direction vector----> inverse eye ray ---> inverse of the cross product

Maybe this could be simulated ...
Beause fg samples a hemisphere this would result in a total 360 degree sampling (with prevalence towards inv. eye)

I tried to test this by merging the last two of yuor pictures in photoshop (inverse eye ray normal at 66% blend mix, eye ray normal at 33%)

Hm ah well... no idea if this looks any more realstic, probably some more renders and teting required ~o)
Attachment:
hairblend.jpg
hairblend.jpg [ 63.04 KiB | Viewed 3233 times ]

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 Post subject: Re: Kristinka Hair Tests
PostPosted: 11 May 2010, 00:32 
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Could I ask where to find AbsoluteWidth and Pixel Unit settings? I am having difficulty finding more information regarding this option.


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 Post subject: Re: Kristinka Hair Tests
PostPosted: 12 May 2010, 22:42 
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There's no setting, you'll need create a set data node and set shapeSizeAbsolute true for each particle

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 Post subject: Re: Kristinka Hair Tests
PostPosted: 13 May 2010, 00:57 
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Thanks for getting back to me on that.

I just spent the last 48 hours trying to pin down a problem I am having. I am getting crashing during render time in 2011. I think I have it narrowed down to a combination Kristinka, SSS, and Final Gather.

I can have SSS and Kristinka in the scene without problems, but once I turn on FG my renders lock up or crashes XSI. Also, I can have Kristinka and FG, but once I introduce SSS to the scene, I get the same problems. I have tried this on several machines in our office. For testing purposes I am using the built in fast sss material.

This is only in 2011, so I apologize if Kristinka is not ready for 2011, or if I have missed information indicating this issue. (or otherwise just messing things up myself) :)


Attachments:
2011 Hair Test.rar [162 KiB]
Downloaded 160 times
2010 Hair Test.rar [138.81 KiB]
Downloaded 138 times
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 Post subject: Re: Kristinka Hair Tests
PostPosted: 13 May 2010, 10:07 
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For me, it looks like Mental Ray can't handle combination of SSS, Hair primitives an FG, where each of these components isn't problematic itself. From my experience, problems can happen in areas with high strand's density - Mental Ray became deadly slow, or you can see a 'lovely' message about firing another 1000 FG points.... then it hangs.

Usually I'm able to solve this by setting 'Max Depth' value in global Rasterizer's render options, to something more than zero - let's say 20, 30.... Avoiding to use transparency on ICE strands, where ever you can, it's also good idea.

Kristinka Hair ICE nodes are just XML, textual files, that communicates with ICE in any XSI version you have, above 7.01. I don't planning any serious updates in near future.

Thanks

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 Post subject: Re: Kristinka Hair Tests
PostPosted: 13 May 2010, 18:59 
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The same thing is happening to my scene. Skin shader, strand hair and FG is a no-go. It's not a problem to split objects up in passes, but FG with Strand hair takes 3 - 5 times as long to render (with SSS objects hidden). We had to dump Mental Slow FG for this project.
Also, I did some render benchmark tests and found that Raytracing was faster then Scanline or Rasterizing. I stopped the render on Rasterize because it took way too long. I must be doing something stupid.


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 Post subject: Re: Kristinka Hair Tests
PostPosted: 13 May 2010, 21:18 
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Guys,

I need to say that all images I've posted, were rendered with XSI 7.01. Also, I didn't used mi_sss_skin shader, anywhere. Subsurface is done with some kind of ICE vertex color 'shaders', a bit improved version of these.

If anyone is interested, I'll post last version - these 'shaders' are maybe harder to figure out, there is no 'real' connection to lights or FG - but output is a much lighter for Mental Ray, just vertex colors are rendered.

Cheers

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 Post subject: Re: Kristinka Hair Tests
PostPosted: 07 Aug 2010, 15:47 
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Image

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