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View Full Version : New fast displacement tutorial - Maya->Mentalray


sunit
11-23-2004, 02:34 PM
Hi all,

I've posted a tutorial at zbc:

http://206.145.80.239/zbc/showthread.php?t=22176

A method for good (workable), fast displacement. Who would have thought, surely the impossible. :)

-sunit

Jackdeth
11-23-2004, 05:14 PM
I'm confused.... how is that a useful tutorial? Are you sure that is the correct link?

Any tutorial on MR displacement maps would have to include the Displacement Approxamation Editor and BSP optomizations. Without those two things, you are missing 90% of the tutorial. :shrug:

sunit
11-23-2004, 05:56 PM
Right - this was initially my idea, using approximation editors. But in my testing (which seems to be quite a lot these days), I found this method gives you much faster displacement, for a similar quality.

As for bsp, I'm not going to go into that here - there's a lot of material out there for people to read. This is simply a method to get fairly accurate displacement, using the polysmooth node to derive smoother normals, rather than working with the approximation editor.

Give it a shot, I was surprised as well. There is a file and a downloadable texture.

regards,
-sunit

Jackdeth
11-23-2004, 06:47 PM
I think you might be missing the.. errr... point. In MentalRay for Maya, if you don't apply a displacement approxamtion to the surface, it just applys a default one internally anyways.

All you are doing is increasing the number of surface polygons before it starts sub-dividing the detail displacement polys. Its true that doing that helps with some render speed and RAM issues, but without defining a tuned approxamation its possible that you are building in displacement flicker problems to your models. Some of the tesellation options don't work well for animated deforming objects... and I think the default method falls into that catagory. And again, BSP tree is the upmost importance when dealing with displacements and thier render speed issues.

sunit
11-23-2004, 07:26 PM
I think you might be missing the.. errr... point. In MentalRay for Maya, if you don't apply a displacement approxamtion to the surface, it just applys a default one internally anyways. Right. I realize that the approximation editor applies to what MR is internally applying anyways. I should be more specific - In scenes where there is a lot of geometry, it seems tuning the approximation is essential for speed. I've found that when working with characters, say in a live action setting, manually tuning the approx. editor seems to increase the time MR takes to render the empty areas of the frame. My knowledge of MR isn't as robust as my knowledge of, say, prman -> I've definitely been struggling to find efficient ways to utilize the displacements in MR. The flicker problem could be a concern - the animation tests I've done so far seem consistent, but I've yet to try them at 2k res.

The speed differences are enormous, rendering in 1/3rd of the time compared to manually tuning the approx editor.

I welcome your comments.

regards,
sunit

Jackdeth
11-23-2004, 07:48 PM
The speed differences are enormous, rendering in 1/3rd of the time compared to manually tuning the approx editor.


That doesn't make sense because you can manually adjust the approx editor to be excactly what the default render is doing, thus the render times will be exactly the same because the setting will all be exaclty the same.

sunit
11-23-2004, 08:26 PM
No, you're right. What I realize I have is just the default settings. I think I'll update the tutorial - though, I'm still confused about why the subd approx overrides the displacement approx, rather than working in conjunction with (if you have any thoughts...), but I think this was my initial prejudice against the approx. editor - that I couldn't figure out how to use both the subd and displace approx together.

Ah well, live and learn. I was hoping to make transparent my workflow, but I realize I've landed my self in a can of worms :)

Anyways, thanks for the comments,
cheers,
sunit

Jackdeth
11-23-2004, 08:28 PM
Now that is an interesting problem.... I've never had to use those two at the same time. I'll dig into that one once I got some free time.

Jozvex
11-23-2004, 09:16 PM
I think I read on the Mental Ray mailing list that it's a problem/bug in the way Maya translates the scene over. *goes and searches* Yep, here:

"maya's approximation editor can do subd approx and/or displace approx. as i
mentioned in an earlier email, the two do not work together correctly. maya
exports these lines:

approximate subdivision surface parametric 2. "Triangles"
approximate displace fine view length 0.25 0 4 "Triangles"

but it should be done in one line like this:

approximate subdivision surface view length 0.25 0 4 "Triangles"

this is because in mental ray 3.3 when the two are used in conjunction "The
displace approximation is ignored, and the regular approximation is used.
Subdivision surfaces are refined during displacement in a single integrated
pass...""

sunit
11-24-2004, 11:41 AM
approximate subdivision surface view length 0.25 0 4 "Triangles"

this is because in mental ray 3.3 when the two are used in conjunction "The
displace approximation is ignored, and the regular approximation is used.
Subdivision surfaces are refined during displacement in a single integrated
pass..."" I wonder how XSI exports this line? It looks like the subd overrides the displacement out of maya - but it doesn't make sense to me why this would be a good implementation in general.

regards,
sunit

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