Beginner questions on lookdev and lighting in H

[Nicholas Ralabate]

Hey everybody!

 

I am trying to work up my skills in surfacing by competing in this month's RenderMan challenge.  I am currently using Mantra (because the RfH for RenderMan 22 doesn't come out for a few more weeks) but I have a few extremely basic questions about the workflow.  I am using the Lookdev desktop, and using the built-in test geometry.

 

1. In the light bank data tree, I am only able to change intensity but not exposure.  How can I change this?  Do most lighters work in intensity or stops?

2. In the object appearance data tree, I am only able to assign materials at the object level.  Is it possible to assign materials to groups from this UI?

3. When you lookdev terrain, is it more normal to scale your uv coordinates in the shader network or go back to the geo and use uvtransform to scale tiling textures up and down?  Or do most people just use triplanar projections on background buildings and landscapes?

4. (Technical) I was looking into light instancing and found that with the template light you can write your own light shaders.  But is that only in /shops?  What is the current /mat way to write a light shader?

5. (Technical) I noticed that render times are faster with packed geometry, but then I lose all my material assignments.  Why is rendering packed geometry faster?  What is the currently accepted way to lookdev packed geometry without losing all your material assignments?

6. (Technical) How does light instancing work?  It seems a little strange to me that the instancing tool is completely separate from the copy-to-points SOP.  Is the instancing tool just running a for loop at IFD creation time?  Are there any other common approaches to procedural light scattering?

[StepbyStepVFX]

Some answers :

5 - you need to look at the export options of the shaders into the ifd in Declare Materials : Controls which SHOPs are embedded in the generated IFD. This parameter can be used to force all SHOPs or all Material SHOPs to be embedded even if Houdini does not find explicit references to those SHOPs on the output objects and geometry.

Indeed, when packed, Mantra don’t access the geo attributes until render time, so you need to export all your sheders so that they are mentionned in the ifd before rendering.

More info here : http://www.sidefx.com/docs/houdini/render/ifd_workflows.html

And here : http://www.sidefx.com/docs/houdini/model/packed.html

 

6 - there are several ways to instance objects or lights in Houdini. One is instancing packed primitives (see above), using copy to points sop. Another is using point instancing, which happens at render time. You can instance lights in both cases, but point instancing is my prefered option, as it seems to me the memory is better managed.

here is a nice tut : 

 

[davpe]

Hey, these are my points of view:

1) and 2) i never use any of those tools (Light bank or Object appearance tab). there is not enough features to make either of them convenient to use. To me it feels like they started the idea of having a dedicated interface for managing lights and objects but then they never came back to make it really useful. However. If you want a comprehensive material assignment solution, you need to look into Material Stylesheets. That is something being actively developed and it represents the most versatile and powerful way for material assignments and overrides in your scenes. For managing your lights, there is unfortunately no interface other than Light bank. Personally, if I have a ton of lights in my scene I use combo Tree view (with lights filtered by name) and Parameters window and it just does the job for me so I'm not even missing Light bank kind of thing very much.

3) When I do terrains lookdev, I have actually always done it procedurally so far with Mantra without using any uvs. Anyways, if you scale uvs I think it is safer to do so in the shader so you can use the original uvs to actually paint a texture if needed.

4) never walked too far in realm of light shader writing but right now I'd say you can only do that in shop network (don't take this for granted thou)

5) previous answer already directed you the right way, I might add that (again) Material Stylesheets is something you may want to explore. The video posted by StepbyStep is very old, and although still valid in key things, material workflows have changed a bit since then. 

cheers.

Edited October 1, 2018 by davpe

[StepbyStepVFX]

Indeed, Material Stylesheet are really fantastic when it comes to bring variations to instanced packed objects, but also for other purposes (I am just a hobbyist :-). Here are 2 videos (part1 & 2) that brilliantly - Jeff Wizzard Wagner - explain how it works (and they are only 6 months old !).

 

[Nicholas Ralabate]

Thanks for the answers!  So much info about instancing and style sheets, this is great.  

For the object appearance data tree question, it looks like if I name my groups and export as alembic then re-import the alembic I can assign materials to sub-groups in the object appearance data using packed edit:

http://www.xuanprada.com/blog/2018/9/22/houdini-as-scene-assembler-part-02

Going to keep looking and see if there is a way to do this without the Alembic round-trip.  Thanks again!