Does Mantra have an equivalent to mental ray's geometry shaders?

What do they do?

A mr geometry shader generates procedural geometry or other scene elements. It is evaluated before any other kind of shader. I like to use this sort of shaders in XSI especially when having a mass of characters or tons of redundant geometry.

There are several things that may be relavent.

1. Render from file, this means mantra only loads the geometry straight of disk as and when it needs it, completely bypassing any cooking/loading of sops. Very efficient for very large datasets. We use this all the time, it's great. Thousands of objects can be stored in an ifd file (Houdini version of rib files) as references only keeping them very small.

2. Instancing, usual sort of thing instancing geometry to particles etc.

3. Houdini procedurals - I've never used it though so can't comment on how well it works.

All of these things are set up under the render tab of each object at object level.

That sound very interesting! I'm not interested in an instancer and I don't want to have the master objects in the scene. I would like to write sequences of plotted envelopes or shapes of some hundred objects onto the disk and read them at run-time from the Shader or Mantra. Can I do that with the first option you mentioned? Houdini procedurals are also very promising because I'm looking forward in parsing the geometry from a custom file format. But for that it seems I have to do some coding with the HDK. It would be nice if I can get around with the .ifd format.

While it's true that you get more power by writing custom procedurals in the HDK, you can always use the prebuilt RunProgram procedural to spawn your own parser which then outputs a .geo file. I've never tried it myself though.

Wait, what do you exactly mean with the “prebuilt RunProgram procedural”?

The RunProgram is a Mantra Procedural. You can find that in your Geometry Object (under Render tab > Geometry, then change “Geometry as is” to Procedural. So you can write your own geometry program that will get called at rendertime.

I think you might still have to comform to the Houdini's .geo format, I think… :?:

you can use “read archive” or “delayed read archive” of renderman also.
I think it would help you…