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royter
05-21-2007, 06:18 PM
I just finished a game concept project 2 weeks ago. You can check the blog and watch the game preview: http://sor.typepad.com/



It was 3 month of intense work; I used both Maya 7 and 8.5, and Mental ray.

It was a constant struggle with the mental ray implementation in Maya, I spent 60% of my time solving problems and 40% of my time designing, building and lighting the scene.



I have been using mental ray for 4 years now, and I just don’t understand why basic and simple things witch exists in other renderes don’t exist or work properly in Mental ray especially in Maya 8.5.



1-Why isn’t the diffuse value of the Maya Lambert shader equal to the diffuse value of the mental ray Lambert shader? Even if I set both the color and diffuse value of the Maya Lambert shader to 0.5 and the diffuse value of the Mental ray Lambert shader also to 0.5, when I render the mental ray shader is way to brighter.



2-a-Now, thanks to Autodesk we can preview the textures of the mental ray shaders in the view port. But we all know that the right way to apply a texture to a mental ray shader is by applying a:

mib_texture_vector plugged to mib_texture_remap plugged to mib_texture_lookup (witch contains the texture) plugged to the diffuse slot of a Mental ray Lambert shader.

Unfortunately you can not preview that kind of texture in the view port (witch is the right way to apply textures to MR shaders……) Why is that?



b-Now to preview textures in the view port, you have to assign a texture to a MR shader the same way you assign a texture to a Maya shader, by plugging a simple 2d_texture_file to the color or diffuse slot of your MR shader. Great… isn’t it!



But if you render the same geometry with a texture assigned to a MR shader as in “a”(witch is the correct way but you cannot preview it in the view port), and then render the same image but with the texture assigned to the MR shader as in “b” with filter turned off in the 2d_texture_file options (witch you can preview in the view port but is not the correct way to apply a texture to a MR shader), and zoom really close into both images, you will notice a little difference. Why is that…Why isn’t both images exactly the same?



3-When you want to light your scene with an IBL but you want your reflections to be generated by another spherical image than the IBL, you can assign an image plane to your camera (with a simple Maya env_ball or env_sky assigned to it) and check “visible in reflections” in the “render stat” options of the image plane. But the image never shows in reflections….why is that? Why doesn’t it work as it should be?













4-Now to resolve this problem you could use a CTRL_ray_node. But what if you want a reflection map 1 for your car windows and another reflection map 2 for your metal?

You could override the reflection slot of your shading group options. But there is 2 problems:

a-It never gives you the same result of reflections (even if you assign an mib_lookup_spherical or a Maya env_Ball) like you would have in an IBL reflections.

b- You will get artifacts (ugly spots that show in all your scene).

Why is that?



5-When (black and white) bump or transparency textures files are converted to the .map format, they don’t show up in the render. Is there a problem with the .map format (imf_copy -r –p) and the grayscale textures? Why doesn’t it work?



6-When applying the mia_sky even if I turn off the HAZE option, the mia_sky seems to whiten the textures especially distant textures. Why is that? Haze is turned off!



7-Multiple UV sets works fine with Maya shaders. But if you want to assign multiple UV sets to geometry with the mix8layers shaders then good luck! In the UV linking options you cannot see the multiple texture files assigned to that shader in order to assign different UV sets to each texture. Why is that? If UV linking was invented it was meant to be used with layered shaders, then why don’t we have that option?



8-Why can’t we assign a layer that is completely transparent to the mix8layer shader?

I tried assigning transparent Maya shaders, mental ray transparent compositing nodes, Maya path material; nothing gives you a layer that is 100% transparent. Why?



9-Why doesn’t both linear and deformation motion blur work properly with animated meshes (with deformation, like moving characters)?



10- Why is Mental ray in Maya 8.5 always out of memory? I tried many known methods, and nothing seems to work as it did in Maya 7 (witch never runs out of memory if you use a low memory limit).





I hope that Autodesk will stop working on unnecessary updates and focus on the real problems like the Mental ray implementation in Maya:

Memory problems, reflection linking etc… should be one of there big concerns.

Please make things simple!





Roy A.

hominid
05-21-2007, 07:25 PM
Regarding question 7 & 8 - Autodesk has nothing to do with the creation of the mix8layer shader, I think your frustration is misdirected.

royter
05-22-2007, 12:55 AM
I Don't think so.

Autedesk nows very well that a big part of Maya users , do use the mix8layer and other ctrl_shader when they use mental ray. Even if Autodesk are not responsible for sush element in mental ray, the problem still remain in the MR implementation.

Hans-CC
05-22-2007, 03:42 AM
1 - it seams that you are forgeting the ambience value try to take it to black
it work's fine for me.

2 - you can try mad_useMRTex script works pretty nice !!
http://www.highend3d.com/maya/downloads/mel_scripts/rendering/mental_ray/mad-useMRTex-4481.html


3 & 4 - i dont use much ibl but why not just create a sphere an edit its render flags to make it visible only in reflections !! i dont think its to much trouble and it renders well ,as the reflection linking i agree with you its very handy to have it .

5 - i cant help you with this one -- sorry !! i have to make a few tries later.

6 - there is a very long and interesting thread about this topic , i recomend you to read it.

http://forums.cgsociety.org/showthread.php?f=87&t=452901&page=1&pp=15

7 - in this point you are probably right, but i think the problem its that it was no think this way since mix8layer its not autodesk's. so keep your uv's in map1 as posible to avoid problems.

8 - i dont see why you want a tranparent layer in the mix8layer , the hole purpuse of this shader its to mix colors , textures, shaders , etc.. , i will be usefull to know what is exactly what you want to do !!

9 - also need more info on what your problem is , but im guessing you maybe forget the motion steps attribute increase it and you will have better results at a cost of longer render times.

10 - well actually every render gets out memory i personally had really hard times with final render in 3dsmax but thats was probably my inexperience with it but back to mr take in mind the way your scene is made ,i personally try to make things as ease as posible to mr for example if you have a dozen models that can be one just one why not combine them !! i've notice that mr behaves better and maya translate the scene faster when you do this instead of have every polygon its own in the scene (i mention this because i have seen this happen alot )then if you are render nurbs,subDs,displacements or polygons that need to tessellate at rendertime use the aproximation editor to control how much you really need , and so many other things.. that you probably now.

one thing i agree with you is that mr should be easer to work with in maya , i have used it in max and my personal feeling is that it is easer in max than it is in maya but the side effect of that is that i fell that in max you don't have all the control over it that you have in maya (in my personal opinion).

i hope some of this help you. and your video game looks nice.

Hans

Ash-Man
05-22-2007, 03:14 PM
maybe you should post this in "the area"

http://area.autodesk.com/

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