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bjoern
10-02-2007, 09:26 PM
Hi, I'm getting crazy here...

This is my Scene (corresponding image below)
-2 Polyspheres and 1 Plane
-- The left with Mia Material (Preset : "thick_Glass") and the right with an Blinn (Color=Black and 100% tranceperent)
-1 Spotlight with Raytraced Shadow

-RenderGlobals Preset : "Production"

MayaFile : Mia_GlassShadow.zip (http://www.bjoerngromoll.com/Forums/CGTalk/Mia_GlassShadow/Mia_GlassShadow.zip%20)

PROBLEM: Why is the Shadow of the Sphere with Mia_Material black?
What could be wrong?
After that image below, I've bin going through all Mia, Light and RenderGlobals parameter... and Set everything to min20 what has todo whis Reflection,Refraction or Shadow Rays...
But nothing... Still the same black shadow :(
THX for any help!!


http://www.bjoerngromoll.com/Forums/CGTalk/Mia_GlassShadow/Mia_GlassShadow.jpg

dagon1978
10-02-2007, 10:44 PM
plug the mia_material in the shadow shader slot under "mental ray > custom shader" ;)

if you use photons plug it in the photon shader slot too

(or use maya 2008 ;))

bjoern
10-02-2007, 11:06 PM
thx Dagon!

It work. But looks a bit weird... What do you think?

http://www.bjoerngromoll.com/Forums/CGTalk/Mia_GlassShadow/solid.jpg


below it looks close to the BlinnShader (Thin Walled under Refracrtion in Mia is here ON), But now the Spehre doesn't look the Same... Any Idea Dagon?
http://www.bjoerngromoll.com/Forums/CGTalk/Mia_GlassShadow/thin.jpg

bjoern
10-02-2007, 11:13 PM
with adjusting the refraction Index, the Spot in the middle of the altered.
But it looks still not right. Right? I meen there has to be smooth gradient...?!

dagon1978
10-03-2007, 12:36 AM
if you like the shadows of the "thin walled", use 2 different mia_mat
the solid for the surface
the thin for the shadows ;)

there are not "right" shadows here, you have to use caustics to make it "right" ;)

davesink
10-03-2007, 02:21 AM
plug the mia_material in the shadow shader slot under "mental ray > custom shader" ;)

if you use photons plug it in the photon shader slot too

(or use maya 2008 ;))

Hope you'll excuse a relatively new user trying to follow along here. When you say"plug the mia_material in the shadow shader slot under "mental ray > custom shader" do you mean in the SPOTLIGHT'S mental ray > custom shader tab?, cuz that's the only place I could find "light shader" and "Photon Emitter" fields. If so, when I plug in the mia_material1 into the spotlight's "Light Shader" field, I just get a black render. Sorry to be dense, but any idea what I'm doing wrong? Thanks!

achoury
10-03-2007, 02:46 AM
Hope you'll excuse a relatively new user trying to follow along here. When you say"plug the mia_material in the shadow shader slot under "mental ray > custom shader" do you mean in the SPOTLIGHT'S mental ray > custom shader tab?, cuz that's the only place I could find "light shader" and "Photon Emitter" fields. If so, when I plug in the mia_material1 into the spotlight's "Light Shader" field, I just get a black render. Sorry to be dense, but any idea what I'm doing wrong? Thanks!

hi
selcet your mia_material in hypershade and clic the input output connections
so u have mia_material1 and mia_material1SG (ShadingGroups)
ctrl a in ShadingGroups, clic mental ray tab and scroll down to Custom Shaders, that's all
hope this help
sory for my english
rachid

davesink
10-03-2007, 03:02 AM
Thanks for the quick answer, rachid, It worked great! (and your English is excellent.)

Kako
10-03-2007, 03:05 AM
That's what you get in maya 8.5 if Fresnel reflection is on.
Turn it off and you'll have something close to what you were expecting (regarding the shadows):

http://img.photobucket.com/albums/v179/KakoCG/glass_shadows_noFresnel.jpg

Or you can use caustics, as Dagon already said.

However, in maya 2008 the raytraced shadows work the way they should even with Fresnel reflectivity on.

http://img.photobucket.com/albums/v179/KakoCG/glass_shadows_2008.jpg

Kako.

bjoern
10-03-2007, 06:18 AM
Where can I find the Attribute "Fresnel reflection" (I'm using 8.5 sp1). Maybe I'm blind, its early here... :-)
Do you meen fresnel under BRDF in the Mia?

bjoern
10-03-2007, 06:50 AM
I get this (Left,) with fresner Off under BRDF. But now the Reflection seems to change.
What not happend in your image. Did you something else?

Right is just the Old view to compare....



http://www.bjoerngromoll.com/Forums/CGTalk/Mia_GlassShadow/Fresner_Off.jpg

bjoern
10-03-2007, 06:54 AM
Another Question :)

When i turn of "Emit Specular" in the Spotlight the Mia ignores it completly.
Is this also fixed in Maya 2008?

MasterZap
10-03-2007, 12:57 PM
It is quite true the shadow behaviour was modified for 2008. While the original was "intentional" it wasn't really "physical". What happens was that shadow rays were hitting "total internal reflection" situations on the inside of the glass... but... that only happened because these rays dont actually refract... had the ray really refracted, it wouldn't have hit total internal reflection.

So the "old" way could cause a quite normal window pane to actually transmit NOTHING at certain angles, which isn't particularily accurate. So we changed it for 2008 not to apply the "total internal reflection" logic for shadow rays. (Basically, the shadow model for "thin walled" is used regardless, as no shadow model is "100% correct" - except caustics)

Another Question :)

When i turn of "Emit Specular" in the Spotlight the Mia ignores it completly.
Is this also fixed in Maya 2008?

The feature was added in 2008. (I.e. that mia_material decodes maya's light flags.)

/Z

Kako
10-03-2007, 01:33 PM
I get this (Left,) with fresner Off under BRDF. But now the Reflection seems to change.
What not happend in your image. Did you something else?

I think I rendered only the shadow region over the original version. I should have mentioned that. Sorry. :D

Kako.

MasterZap
10-03-2007, 01:58 PM
I think I rendered only the shadow region over the original version. I should have mentioned that. Sorry. :D

Kako.

A standard fresnel glass reflection is fairly close to the non-fresnel mode with the "0 degree reflectivity" set to 0.05 rather than the default 0.2 - this accounts for the difference. If you set it to 0.05 you'll be hard pressed to notice a different to "fresnel mode". (The curves graphed on top of eachother are nigh identical)

/Z

bjoern
10-03-2007, 04:04 PM
Thx Zap, and everyone else!! :)

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