Instancing group of objects

[salvati.marc]

Hello everyone.

I m trying to instance objects using set_instance_geometry.

First trial with  single objects works well. 

But when using objects composed of multiple objects (tree + leafs, flower + petals ...) then it becomes tricky.

I tried to use the merge node before sending to the set_instance_geometry node. It did work, but the shader of both objects are lost. 

I tried to use build array node, thinking that an array in the instance list would be considered as a whole, which is not the case.

So another solution would be to use multiple set_instance_geometry nodes with the first part of each object, then the second... and use always the same points data for each instancer. but if objects dont have the same number of parts we have to add dummy objects...

I thought about another solution, just use set_instance_geometry with only one object, one id. Instanciate each part of each object separately, and just use common points between objects from the same part.

I wonder if what i try to do is clear... Maybe there is much simpler ways to do that.

if anyone has any ideas...

Thanks in advance.

[jonah.friedman]

Hi Marc,

This is something we're looking to improve in the future. For the moment, if you want to instance an asset composed of multiple objects, your best bet is to instance render archives (AKA: .ass files). 

These have some side benefits, such as supporting the entirely Arnold feature set and time offset instances. 

To do this, export an Arnold .ass file and use the "render archive instance" node. 

[salvati.marc]

thank you for your answer. i didnt thought about it, but yes that is a possibility.

do you have any ideas between the performance difference in rendering/memory using ASS for group of object  VS using as many instancer as there is part in the object?

[jonah.friedman · Accepted solution]

I accidentally clicked "accept solution" just now, please ignore that 🙂

---

@salvati.marc wrote:

thank you for your answer. i didnt thought about it, but yes that is a possibility.

do you have any ideas between the performance difference in rendering/memory using ASS for group of object  VS using as many instancer as there is part in the object?

---

There should be no real performance difference - it's kind of all the same to Arnold whether the geometry was translated from Maya or whether it loaded from a file. The geometry will need to load from disk at the start of the render, but this tends to be fast. Your scene file can be faster to load by not containing the geometry. 

[salvati.marc]

ok. i ll try both and compare. If i dont need to go through ASS, it simplifies the workflow.

[cbrowneL7QTD]

can we now instance multiple objects without using ASS files?

This seems like it should be crazy simple. IN houdini simply get a merge node and plug two objects into it. 3 nodes... that's it.

Node basics 101.

How can I combine multiple objects together with different shaders and then instance them all at once?

[Christoph_Schaedl]

Only if you use USD files.

[cbrowneL7QTD]

is there a way to select a single point from the bifrost scatter and delete it?

[Christoph_Schaedl]

You cant select it by clicking. But you can cull it with an object in the graph. Or paint a mask.
https://discord.com/channels/872260298508222534/1152218612296327190/1153288472027725904

https://youtu.be/aGziWy39XU8?si=f1mb5s5j15KG5oY6

[andrea_pinto82]

I don't know if it can be a solution, I used an "iterate" to create instances for each object in the group.

[cbrowneL7QTD]

thank you, can i see one level up? not sure where this is feeding into from?

[andrea_pinto82]

[cbrowneL7QTD]

thank you very much and sorry for the misinformed question

... but where are you're multiple objects feeding into? 'input by path'

what is that and how are your multiple objects going in there?

thanks again

[andrea_pinto82]

don't worry, sorry me if I didn't post a scene.
you can drag your selected objects from the outliner and import them into the graph

[cbrowneL7QTD]

I understand but how are you combining mulitple objects with different shaders?

Are you dragging them in as a group? I can't seem to be able to do that.

Are you merging the geo somehow?

[andrea_pinto82]

I tried an example with 3 different groups. I don't know how manageable it is.

I hope it can be useful.

[andrea_pinto82]

sorry for the double post, I changed the scene.

[andrea_pinto82]

I came across a discussion on Discord and decided to create a video where I reconstruct the graph to achieve instancing of a group of objects in Maya Bifrost.

You can check out the video here:

https://youtu.be/Lvl-OddE4PY

I hope this helps anyone looking to implement this solution!

Apologies if the video is a bit long and perhaps somewhat disorganized. 😊