I find u ambient occlusion having bad artifact…


No matter which scenes i render, i m bound to have the bad defects…
anyone please guide…

I attached Clay and placed a environment light in the scene with area shape set to “Environment”.
Please advice

I'm no pro yet but my understanding of getting ao in a scene is by adding a light template at scene level and assigning a vex global illumination shader to it.

Then play with the shader's global tint to get darker and brighter results and the shader's sampling to reduce noise at the expense of time.

see my file attached

The black artifact comes from the Clay shader, not the AO. This is a long-standing issue with the clay illumination model.

A problem compounding this is that your boxes have consolidated points and therefore being smooth-shaded. Append a Facet SOP (Unique the points or Cusp) to fix that.


PS. If you want an alternative to SESI's Oren Nayar clay shading that doesn't give you those artifacts, you might consider a VEX port of LocIllumOrenNayar from here: http://www.renderman.org/RMR/Pubs/arman/shaders/locillum.h [renderman.org]

omg… indeed a houdini expert….
need advce and how to make the header file works in houdini.
please guide, i m interesting into renderman shader too…

I tried Facet but it doesn't seem to work for ambient occlusion on the particle fluid. please advise… anyone?

can you post the scene? and have you tried my setup? and have you tried Jason's suggested shader replacement?

hi, i tried jason's method and the facet sop works perfectly on geometry…
but for dynamic object such as particle fluid, it didn't work.
I am looking at the alternative shader. But i do not know how to use the header file that he was referring to.

If you know, please advise…

diskhub
hi, i tried jason's method and the facet sop works perfectly on geometry…
but for dynamic object such as particle fluid, it didn't work.
I am looking at the alternative shader. But i do not know how to use the header file that he was referring to.

If you know, please advise…

I was kinda indirectly suggesting you switch away from using the VEX Clay shader - to something like a VEX Plastic. It's the Clay that is the real problem and Faceting will only help with object which you want to appear faceted.

Even if the Clay shading didn't have this issue, you probably don't want to shade the particle fluid like clay anyway It's not a very fluid-like lighting model.

The header file is from a PrMan RSL implementation of a clay lighting model and I thought if you were ambitious you could quickly translate it to VEX :wink:

nice one!
Sad to say, i am not a shader guy, but i dun mind listen to ur advice
if u can guide me or where to find link on how to write a VEX shader?

Meanwhile, i will try other shader. Is there a lambert alternative in VEX shader library?

Hi,

To get a Plastic shader, you can either drag & drop a Plastic material from the Material Palette or go to SHOPs, hit Tab & select the VEX Plastic shader. To get Lambert shading, all you have to do is to set Specular to 0.

Here is a thread [sidefx.com] for rendering fluids.

I also recommend checking out the Learning menu at the top of this web page. There are lots of tutorials to get you started.

Last but not least, I noticed you're from Singapore and so am I. It's good to see one more Singaporean getting into Houdini. There is another new user over at odforce's forum too.

Welcome to Houdini-land!

Cheers!
steven

yea, i know abt the shaders… just curious on how to port the renderman shader to vex shader… so wanted to ask more from jason.

anyway, nice to know there's a singaporean working in this industry with houdini!

Hey,

As for translating Renderman shaders to VEX, you can check out these two [forums.odforce.net] threads [forums.odforce.net] over at odforce. There are more but both are good to start with.

There are other [forums.odforce.net] Singaporeans using Houdini too.

Cheers!
steven