Shadow - Once Again

[Visual Cortex Lab]

Sorry again for my post... but i really dont get why it seems I'm doing something really special while i'm not.. and I dont get any result or solutions.

Shadows trought Glass or just transparent objects.

brand new scene.

I've a grid GEO as a floor (with a plastic or anything else material).

a Box GEO as a glass (with VEx glass, or Vex Supermaterial)..

a Cone Light as a light (with or without shaders)..

that's it. I just have plain black shadow.

shadows are plain Black. the Box has been shaded with SuperMaterial, VEX Glass, no way to get shadows properly casted as I'd expect. When I color the transparency I should get Colored Shadows, aint it?... no way.. plain black shadows.

It takes longer to explain my problem that really figure it out.. i just cant get correct shadow from transparent objects .. i tried all glassy shaders from Houdini otl (vex glass, supermaterial) and all type of shadows shaders for the light, shop and no-shopped...

what i might be stuck with is the Mantra Ray sampling maybe.. which i'm not familiar yet (i'm a really newbie).

please, can anybody guide me trought this simple process?

thanks a lot in advance.

[sibarrick]

Could you post the test file that you have? it will be way easier to answer if we can have a good look at the file.

[Visual Cortex Lab]

the scene is the simple setup.

no ROP has been created cause I wish to know where do I set the ray bounces in Mantra therefore i wait for your tips

i just applied the VEX GLASS shader on the box now ... and no shaders on the light except setting FilterShadows.

jsut click VIEW:MANTRA and see the result... shadows are black... while they should be grey cause of the box transparency.

I set refraction to 1.0 cause i've been told this shader have a problem with refraction and shadows..

i'm now expressingly asking if VEX glass works or not... i'm just trying to get a damn glassbox to casts proper shadows since i wish to render out the "Pins tutorials" which i made the scene from, but since the front part is a glass, i cant get the proper render out

http://mimgfx.homeunix.net/pins_head_1.jpg is what i'm trying to get out of the scene... the scene has been made (thanks to such tutorial) time ago in Houdini and then rendered out with XSI .. now i was trying to get it shaded and rendered in Houdini with Mantra to learn how to do it.. but then i got stuck with the front glass.

hope this helps to see my problem.

shadows.zip

[sibarrick]

Ok, the answer is a little tricky as you have to get your hands dirty with vex or vops.

Unfortunately the shaders that come with houdini by default aren't the greatest and the glass ones in particular aren't all that clever.

The glass shader you have on the box because it can refract has to set the Of (opacity value) to 1. But there is no reason why the shadows shouldn't be transparent, but to make that work you have to either change the code or write your own shader.

If you look at the attached what I have done is to modify the VEX glass shader so that if it detects it is being called by a shadow then it make the surface transparent, if it is doing it's normal shading it isn't. The intensity of the shadow now depends on the transmit value, the more light it transmits the more tansparent the shadow.

shadows2.zip

[Visual Cortex Lab]

sibarrick, thanks a lot!

you clarified pretty much my question and problems about it... at least I now know that i wasnt doing anything "that" wrong.

strange tought that Houdini ships with ... "defective"? materials/shaders... i mean... for the basic ones. odd.

can you also please tell me how to handle.. mantra about Raytraces?... in MentalRay i usualy tells mins/max/avg numbers of ray bounces, specially when talking about glass materials to define refraction/transp/reflections acuracy as well... how can i do that in Mantra?... apparently by tweking the Ray decoupling nothing changed here..

again, thanks a lot.. i'll study you vex shader and I'll try to write my own glass shader... well.. my first shader then.. guess i'd start with something easier

thanks

cheers.

[Jason]

sibarrick, thanks a lot!

you clarified pretty much my question and problems about it... at least I now know that i wasnt doing anything "that" wrong.

Hi Sum][one

Simon probably answered a little more clearly than I did in this post -

The shaders that ship with Houdini have always been under mild criticism because many of them were built as "examples" for what you could achieve in Mantra. Since then SESI has added several shaders - like the VEX Gallery shaders but never gone back and fixed the basic original shaders that were shipped since the Houdini 4 distribution. I'm not clear why.. perhaps to maintain compatibility with old scenes? dunno. Mantra has evolved so much since then that it couldn't render those legacy scenes to look the same in anyway so my opinion is that they should be given the once-over and modernized, optimized and foolproofed before 8.0 release.

Anyway, welcome to the gritty world of shader-writing! Hope you enjoy it

[Visual Cortex Lab]

Hi Sum][one

Simon probably answered a little more clearly than I did in this post - 

The shaders that ship with Houdini have always been under mild criticism because many of them were built as "examples" for what you could achieve in Mantra. Since then SESI has added several shaders - like the VEX Gallery  shaders but never gone back and fixed the basic original shaders that were shipped since the Houdini 4 distribution. I'm not clear why.. perhaps to maintain compatibility with old scenes? dunno. Mantra has evolved so much since then that it couldn't render those legacy scenes to look the same in anyway so my opinion is that they should be given the once-over and modernized, optimized and foolproofed before 8.0 release.

Anyway, welcome to the gritty world of shader-writing! Hope you enjoy it

20741[/snapback]

Oh Jason, please accept my apologies to not having been thankfull with you.. honestly. I'm enjoying so much people like you in this forum which answer to my noob questions so promptly really..

I've downloaded all i found about Renderman and a bit of VEX (hard to find for noobs).. and I'm seriously getting into the mood of starting myself to learn it seriously, which i dont expect will happens too fast tought

Sorry again and yeah, thanks for your replies as well... what i was missing from the other thread maybe was just a further step on the glass problem by having something concrete to handle and see what was wrong.

Now i'm trying to understand differnt approach to those glass shaders found around (Mario, Simons) and try to build my own as a start to understand how to write a shader... will be hard i know.. but i have to start with something

again, sorry and many many thanks for your time and patience

cheers

[Visual Cortex Lab]

there's still one question which i need an answer...

in Mental Ray i'm used to set Raybounces for final render and test renders... which glasses are mostly affected by .. is the same with Mantra's "Decouple ray sampling" settings? if not.. what is the parameter to rise/lower the ray bounces? (black areas inside a glas object are usually archivied from low ray bounces afaik.. )

cheers

[Jason]

there's still one question which i need an answer...

in Mental Ray i'm used to set Raybounces for final render and test renders... which glasses are mostly affected by .. is the same with Mantra's "Decouple ray sampling" settings? if not.. what is the parameter to rise/lower the ray bounces? (black areas inside a glas object are usually archivied from low ray bounces afaik.. )

20745[/snapback]

Hey there,

You can still set hard limits for raybounces and such for Reflections .vs. Refractions in the Object level parameters -switch to the Render tab. You'll see those fields appear in the list. As you've guessed, the Decouple Ray Sampling is not related to the ray depth - it only controls the number of rays shot out from the Micropolygon interiors to super-sample (antialias) your reflections and refractions.

You can also customize shaders to bear some of this ray-depth intelligence but that's not often necessary.

Have you looked at these simple shader-writing tutorials?

Hope this help ya

Jason

[Visual Cortex Lab]

Hey there,

You can still set hard limits for raybounces and such for Reflections .vs. Refractions in the Object level parameters -switch to the Render tab. You'll see those fields appear in the list. As you've guessed, the Decouple Ray Sampling is not related to the ray depth - it only controls the number of rays shot out from the Micropolygon interiors to super-sample (antialias) your reflections and refractions.

You can also customize shaders to bear some of this ray-depth intelligence but that's not often necessary.

ah cool.. i'm checking it out right now.

Have you looked at these simple shader-writing tutorials?

Hope this help ya

Jason

20746[/snapback]

yup.. and I've noticed you didnt finished the "displacement shader" (coming soon )

really helpfull tought.. this will be one of those docs i'll grab on my laptop for "nights reading" next weeks.

cheers

[Jason]

\yup.. and I've noticed you didnt finished the "displacement shader" (coming soon )

20747[/snapback]

Heh heh.. yeah.. the only reason why I haven't finished the displacement shader section is because it's really so much easier than surface shading. All the BRDF stuff, reflections and refractions, fresnel and such nonsense doesn't rear its ugly head in the Displacement context. It's all about pretty patterns, displacement mapping and manipulating noise and so on. The only things you have be really aware of here is filtering issues on really noisy surfaces and selecting the appropriate Shading Quality to make it look the best for the performance hit it'll cause.

And with VOPs this gets even easier since many of the functions are antialiased and there are plenty of cool pattern-generators in there.