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material instance creation

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Maschinenfabrik
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Joined: March 2016
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I'm having difficulties creating multiple material instances and overriding the textures with the one my HDA creates for every mesh I generate.

No matter what I try I only get one instanced material and it does not set the corresponding texture for it.

I tried using the split attr on the unreal_material_instance attribute but I guess it only works for instanced copy to points geometry? I added a copy to points to see if it would make a difference but sadly it does not.



My current setup;
I am using a TOP network to load in the geometry and textures. I process every workitem with this for the file import 
`pdginput(0,"file/geo",0)`
and assign a different material on each iteration which works although I have the feeling I am doing some really hacky things to get the hda to create a different material with textures for each mesh which was also a pain to get working.



I have this python script in my topnetwork to fill the texture paths;
# Executes a Python script, either in process or as a job
#
# The following variables and functions are available in both case:
# work_item
# graph
# intData, floatData, strData,
# intDataArray, floatDataArray, strDataArray
#
# In addition to the above, in-process scripts can also access:
# self         - the current PDG node
# parent_item  - the parent work item, if it exists

import hou
matnetRef = hou.node("../../matnet1")


#children = matnetRef.children()
#if(matnetRef.children()!=0):
#    for n in matnetRef.children():
#        n.destroy(True)
    
pdgInput = parent_item.inputFiles[1]
wedgeindex = work_item.intAttribValue("wedgeindex")



material = hou.node("../../matnet1/principledshader"+str(wedgeindex))
#material.parm("basecolor_useTexture").set(1)
material.parm("basecolor_texture").set(str(pdgInput[0]))

materialName = str(material)

#work_item.setStringAttrib("materialNodeName",materialName)
work_item.addEnvironmentVar("materialNodeName",materialName)

I get a material with textures for every processed mesh but I don't get more than one material instance



I also unsure if this is the right way to go. If anyone has any ideas or could take a look I would very much appreciate some help

Attachments:
object_las_.dev.ProcessInputScans.1.0.hda (1.7 MB)

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leKryuk
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Joined: Sept. 2022
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Hello

I have encountered the same problem.
Essentially, we have two options:

- The first option is to create a new material for each new object in the scene for which we would like to apply a material with modified material parameters. However, this approach is not optimal as the material instance was designed for these purposes.
- The second option is to create only one material instance, even though we cannot control its name. What's the point of being able to control the parameters of a material instance if we cannot create more than one instance?

I believe one of the issues stems from the fact that we cannot control the name of the created instance. We have one parameter called "unreal_material_instance" where we can reference our master material. However, the system does not automatically create new instances when it encounters new values for the material instance parameters.

Attachments:
01.png (326.2 KB)
02.png (297.3 KB)
03.png (223.4 KB)

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Maschinenfabrik
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However, the system does not automatically create new instances when it encounters new values for the material instance parameters.

Yes that seems to be the problem! I gave up trying to get it working solely using houdini engine. At the moment I am creating the material instances with a python in editor script in unreal after my static meshes have cooked...it's not the "one click solution" I was hoping for but it does work for now
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Groterhooge
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Joined: Aug. 2020
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I've been struggling with the topic of this thread as well, but the work around is to set random parameter of Material Instance (hereinafter referred to as MI). Imagine, you have 2 packed primitives. You need to set up different MIs of one Master Material. In order to get two different MIs, you should set parameter to a different value, i.e. parameter Roughness. One packed primitive will have value of 0.75, and another one will have 0.76

You can do it with 
unreal_material_parameter_roughness
if your MI has parameter with the name of "Roughness". Read about this in the documentation.

Also I found out, that those attributes can be placed inside packed primitives and Unreal will find and read them afterwards
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