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sumpm1
12-09-2004, 03:03 PM
I have been working with Zbrush and now I want to use the displacement maps in XSI. I realize that the best displacement map renders are going to come from a renderer with micropoly aka subpixel displacement ala renderman and the new C4D.

Believe me I have searched every thread at CGTalk, 3dBuzz, ZBrush, Softimage.com,and Spiraloid to find whether or not Mental Ray supports this feature. The main listings say that these renderers only support micropoly displacement:VRay, all Renderman renderers, Final Render, C4D R9.

That's it, none of the lists mention Mental Ray. But...... I have read in a few threads that it does: Here (http://www.cgtalk.com/showthread.php?t=76869&highlight=subpixel+mental) , Here (http://www.cgtalk.com/showthread.php?t=41041&highlight=subpixel+mental) , Here (http://www.cgtalk.com/showthread.php?t=139583&highlight=subpixel) , and Here (http://www.cgtalk.com/showthread.php?t=25674&highlight=subpixel)

If someone has a DEFINITE answer on this subject please tell me.

maxx10
12-09-2004, 03:30 PM
since 3.1 mR has true sub-pixel displacement

http://www.mentalimages.com/2_1_1_technical/

Just_David
12-09-2004, 03:30 PM
From mentalImages.com

displacement mapping:
separate refinement approximations: parametric, edge length, distance, angle; view dependency..

ew very precise sub-pixel displacement that resolves even the finest detail of the displacement map, without excessive memory consumption and with very easy-to-use quality control settings, using mental ray 3's dataflow mechanism.

el_diablo
12-09-2004, 03:32 PM
If you use View Dependant subdivision then you get about the same effect, that is no triangle bigger than 1 pixel (with default settings).

Still, I dont think mental ray is on par with renderman subdivision. In my expirience it uses way too much memory and is too slow to be fully usable. However for rendering zbrush displacement maps for one object in scene it should work good enough.

I'm only a XSI novice tho, so all is AFAIK.

sumpm1
12-09-2004, 04:06 PM
That's very good to hear Maxx10. I would have expected that the biggest name in rendering keep up to date, and the technical document says that it supports them without excessive memory usage, which sounds great.

Now, do you have any idea how to enable or modify the settings? This could be a case of RTFM.

maxx10
12-09-2004, 04:44 PM
Uh... unfortunately I'm not an XSI user... so I can't be of any help

Ablefish
12-09-2004, 09:19 PM
One of the best techniques for fine tuning the displacement settings on an object (in the Geometry Approximation ppg), is to apply an ink shader to the camera, and turn on Faceted in the shader. This will let you see exactly how the geometry is tessalated at rendertime by the displacement.

You can tell if your settings are unnecessarily high, or if you're using the proper displacement method (parametric, Length/Distance/Angle (LDA), or Fine. Proper use of View Dependant can go a long way.

You'll probably also need to use some of the vector math or Change_range nodes in the render tree to fine tune the displacement. For example, without changing the range, pure white in your map will equal a displacement of 1, which could easily be too much for your model. Setting Max Displacement (in the GeoApprox ppg again) will crop your map if the values go beyond it (so it's not enough to just turn this down).

Hope that helps,

Atyss
12-09-2004, 09:27 PM
That's very good to hear Maxx10. I would have expected that the biggest name in rendering keep up to date, and the technical document says that it supports them without excessive memory usage, which sounds great.

Now, do you have any idea how to enable or modify the settings? This could be a case of RTFM.
It's called Fine displacement in XSI. Choose this mode when you want that sort of displacement, and check View Dependant.


Cheers
Bernard

Fex
12-09-2004, 10:44 PM
hi ho,

have something to say about micropoly rendering:
there are micropoly renderers and intelligent tessalate tricks for doing pixel displacement while rendering...
micropoly renderes are as far as i know nearly all RenderMan compliant renderes
like PrMan, Air, Pixie and one more quite unknown Houdinis Mantra Renderer;
the one with the tessalate tricks are VRay, Messiah Studio..
The great difference is that micropoly renderes dice the whole picture in polys
that have the size of a pixel ( bigger than a pixel for hi speed, smaller than a pixel
for very high quality stuff) because of that they have all high quality motion blur and
DOF with very low CPU cost comparing to Raytracing or Scanline based renderes.

I read a long time ago that there is a hidden trigger in the MentalRay
file format that switch to micropolygon rendering. Maybe its only for standalone
MentalRay??

sumpm1
12-10-2004, 01:42 AM
Sounds interesting Fex.

Does anyone know how Mental Ray fairs against Renderman and other micropoly renderers, and if their micropoly techniques differ? Anyone have any opinion on the quality of each of these renderers' displacement with these options?

Because I was having a little trouble getting a good output with 'Fine' displacement in Mental Ray. I don't know if it is because of the resolution of my source map.

But I would love to see a heads up test with the same models in these renderers.

sumpm1
12-10-2004, 02:45 PM
I finally got the 'Fine' displacement to work all right. I had to mess with all of the geometry approximation settings. I either had to turn the render subd level up, or turn the 'Fine' settings' length setting down very low which gave me pretty sharp results.

Thanks for the help

Alive_&_Kicking
12-10-2004, 05:22 PM
I read a long time ago that there is a hidden trigger in the MentalRay
file format that switch to micropolygon rendering. Maybe its only for standalone
MentalRay??Yes, it is called Rapid Scanline, but it only functions in a manner similar to the REYES architecture, it is not micropoly rendering. Rapid scanline will tesselate your objects into triangles which size is controlled by your antialiasing min/max settings and then shade those triangles N times. Unnecessary geometry is culled. All that is close to the REYES style. With Rapid you get the fast scanline motion blur. Mental ray also can do scanline depth of field with Raid scanline, but in 3.3 this is not finished completely, let's hope in 3.4 things will be finalized :)))))

REYES micropoly rendering and mr microtriangle tesselation is something totally different (even though it sounds deceivingly close). REYES micropolies are not polygons but bilinear patches...

Cheers

p.s. about Vray's "subpixel displacement" : I remember very clearly reading it's documentation and it was explained that it actually has rough diplacement mapping and then normal map added for the "sub-pixel" part...So you get the idea

Atyss
12-10-2004, 05:22 PM
You can increase the sharpness of the fine displacement with the Sharpness parameter (duh!)


Cheers
Bernard

sumpm1
12-11-2004, 05:37 AM
I wanted to try and use these displacement options to generate a better normal map, but it doesn't seem that distance/angle or Fine modes work for GPU Surface FX.

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