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30-05-2012, 02:02 PM   #1
ctbram
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Vray 2.0 demo
Guys, here is a demo I just watched for vray 2.0 and it looks really interesting. I was particularly interested in the displacement section around 32 minutes into the video.

I have tried to do displacement + transparency in mental ray and after days of pulling my hair out and nearly losing my voice from cussing at the computer I just gave up! Why? Because it should not be as convoluted as EVERY god damn thing is in mental ray!

The way it is done in Vray is the way it should be done! I plan to look into vray.

The Latest in V-Ray, Konstantin Gaytandzhiev, workshop at FMX 2012 - YouTube
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30-05-2012, 03:52 PM   #2
honestdom
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looks like it'll be an interesting video thanks.
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30-05-2012, 05:39 PM   #3
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Sigh* When I look at that I get a bit depressed about MR, but I guess ChaosGroup has to keep up since they don't get bundled. Proxies with animation (and user interface!) and even shader swatches that don't use a black background (it's small fries in the scheme of things but seriously, who thought that was a good idea?) Now I'm wondering, is gamma correction and passes like a non-issue in Vray?
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30-05-2012, 06:58 PM   #4
daverave
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Some thing more to learn thanks Rick........................dave

does look good
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31-05-2012, 01:56 AM   #5
NextDesign
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Quote:
Sigh* When I look at that I get a bit depressed about MR, but I guess ChaosGroup has to keep up since they don't get bundled. Proxies with animation (and user interface!) and even shader swatches that don't use a black background (it's small fries in the scheme of things but seriously, who thought that was a good idea?) Now I'm wondering, is gamma correction and passes like a non-issue in Vray?
mentalray's integration with Maya is poor to say the least; It's much nicer to work with in 3ds max. What most people don't notice, is that the mayatomr plugin is developed by Autodesk to translate Maya objects into the formats expected by mentalray.

With Vray, gamma correction is taken care of with a tick of a box, and passes are done just as easily.
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31-05-2012, 12:37 PM   #6
daverave
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Rick looks like you can do a negative value in the displacement to push the mesh in dont think maya can do that ................dave

http://mayazest.blogspot.co.uk/2012/...-in-v-ray.html
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31-05-2012, 12:56 PM   #7
honestdom
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sure you can do that in mental ray. Maybe the problem is as Rick says you can do the same thing a million ways.
I'm pretty sure i do displacement in mental ray different from you guys.
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31-05-2012, 05:57 PM   #8
ctbram
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Yep,

You can do negative displacement Dave........

================================================== ========================

> 50% grey (lighter) == positive displacement

50% == no displacement

< 50% grey (darker) == negative displacement

You can also play with alpha offset to adjust this value.

================================================== =========================

The problem I have with mental ray displacement is that like most things in Mental Ray it is just to fricken convoluted!

What is the point of having a displacement node for instance that controls NOTHING! There are like half a dozen adjustable settings in the displacement node and I have never seen any of them used for anything!

You control offset distance with color balance, and displacement tesselation with a displacement approximation node.

But still have to set the bounding box using the shape node's Maya displacement section.

Also mental ray has all these freaking knobs and dials but do little to document how to adjust them properly or even describe what their function is for that matter. You go to one dial and you have to increment it in units of a billion to see any effect and then you go to the next dial and if you increment it by .0000001 you've gone out of range!

Verses V-Ray ... You give it a map, tell it max displacement for white, and give it an optional water level. No bounding box, no arcane mystical render tesselation computations. It just works and better still it breaks the task into bite size chunks that even a 32bit machine can handle!

I can sum up all the problems that I have with Mental Ray in one statement....

They take every possible rendering task you can perform in mental ray and then give you so much control over every little arcane internal variable, that in the end you have no control at all!
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Last edited by ctbram; 31-05-2012 at 06:04 PM.
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31-05-2012, 06:16 PM   #9
daverave
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Stand corrected Dom, Rick
Did a test with the approximation displacement that did just as you said, the bound box thingy were did that come from and what does it do never used it, and Rick does Vray have those edge artifact when displacing...............dave
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31-05-2012, 07:02 PM   #10
ctbram
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The bounding box has has been there for both maya and mental ray. What is does is limits the region of space in which the displacement can occur. If you have ever tried to do a displacement and it does not displace as far as you expected it is usually due to the bounding box being to small. It's like a 3D clipping plane for displacement. It supposedly helps maya be more efficient using memory while computing the displacement, but why maya cannot make this computation on its own defies any logic.

The box is computed by looking at the shape node of an object that has a displacement attached to it, based on the color balance value.

So there is a definite order to setting up a mental ray displacement.

1. create the displacement map
2. create a material
3. apply the displacement map to the shader group node (I do it this way rather then connecting to the displacement input of the material because it works for both maya and mental ray materials.
4. set the max displacement for white / black using the alpha gain of the displacement textures color balance node. IMPORTANT - remember to check "alpha is luminance"
5. NOW goto the shape node of the object that has the displacements displacement node and click compute bounding box. You should do this every time you adjust the alpha gain as this determines the size of the required bounding box.
6. Set the render tessellation - for mental ray use a displacement approximation node or for organics a subd approximation node, for maya renderer you use the shapenodes displacement map tab and adjust the feature displacement (initial sample rate) and (extra sample rate) variables. Don't ask me how to logically pick the values though because like all things in mental ray it seems people just pull numbers randomly from their ass!

I have to keep a howto folder for maya with crib notes like this because every time I try to do displacement I cannot remember the right order to do things and where each thing that needs to be adjusted lives. This is why I keep complaining about mental ray being to convoluted!
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Last edited by ctbram; 26-07-2012 at 11:32 PM.
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31-05-2012, 07:08 PM   #11
ctbram
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As for the edge artifacts that is a function of the displacement image resolution (aliasing) and the displacement approximations settings, and how dense the poly count of the object being displaced is. Once again multiple variables that maya leaves totally up the user to try and figure out!

I am a physicist, engineer, and mathematician and there are not many humans that can handle a multi-variable non-linear problem with more then four variables in their heads but this is what you have to do all the time using mental ray. As I have said you have so much control that, in the end, you have no control!
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31-05-2012, 07:21 PM   #12
daverave
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Thanks Rick
I know that the aliasing of the texture was the problem does Vray handle it better............dave
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31-05-2012, 07:26 PM   #13
ctbram
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I am not sure, although it seems to do a better just in general, but I am not sure if it's v-ray doing something special or mental-ray / maya not having some super secret switch or dial adjusted. It's certainly easier and more intuitive to set up though.

Intuitively, the issue for aliasing and displacement, is that any anti-aliasing would be interpreted as displacement. So the only solution would be to increase the image map resolution to increase the pixel density. But that is limited by the physical pixel size of the display.
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Last edited by ctbram; 31-05-2012 at 08:34 PM.
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01-06-2012, 09:33 PM   #14
murambi
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I really want to start to look into vray but damn I sometimes feel like an old dog
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01-06-2012, 10:31 PM   #15
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Well guys, as there is already a thread about Vray, I would like to share with you the articles,which I found very useful to understand individual function of this engine, maybe you have already found and read it, but there they are:

Antialiasing and Color mapping
Indirect illumination
Irradiance Map
Light Cache
GI Engines Choice
DMC Sampler
Raycasting
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