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I am using instances of a petal object to create a flower with Geometry Nodes and I have defined a pin Vertex Group that I want to somehow specify in a cloth simulation:

enter image description here

In Geometry nodes, I'm thinking I have to Realize Instances so that each petal will be cloth-simulated independently:

enter image description here

However, whether or not I Realize Instances in GN, I am unable to specify a Pin vertex group for the cloth-sim:

enter image description here

I've tried to Apply the GN modifier and the object disappears, I've tried Make Instances Real and things go really crazy with many duplicates of the GN object.

Here's a link to an example blend file.

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  • $\begingroup$ maybe i am too dumb, but i can't find any vertex group in your example file for [1]: i.stack.imgur.com/8uAGH.png and no pin entry.... $\endgroup$
    – Chris
    Mar 7, 2022 at 11:33
  • $\begingroup$ @Chris as I understand it, the flower_petal has a pin group as shown in screenshot 1. It's the prototype for the GN instances of the flower. The problem is that the pin group is not added for the instance copies. $\endgroup$
    – Blunder
    Mar 7, 2022 at 13:05

1 Answer 1

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To transfer the vertex group (pin) of the instance object (flower_petal) to the flower object with the Geometry Nodes modifier (Flower_GN.001) you need to do the following:

  • create the pin group on the flower object (Flower_GN.001)
  • add a new input slot (Pin Group) to the Group Input of the flower GN (in the node editor)
  • add a Capture Attribute node between the Object Info (instance object) and the Instance on Points node
  • wire the Pin Group input to the Value input slot of the Capture Attribute node
  • put the Realize Instance node after the Instance on Points node. (It does not work after the Join Geometry node)
  • in the Geometry Modifier settings select pin as value for the Pin Group
  • select the pin group in the Cloth settings.
  • check if the pin group on the flower_petal (instance object) is correct. Note that pin is not the same as Pin when you type the name.

The nodes in black frames have been changed/added.

geometry node setup

Vertex group and modifier settings:

vertex group and modifier settings

Please give the pin group a bit more weight otherwise all the petals hang down limply ;-)

Note about Blender 3.1 RC - When you open the blend file in Blender 3.1 the Realize Instances node gives you a warning about "Legacy Behaviour". In the side panel (N) > Node > Properties there is a checkbox. You need to uncheck it to make the transfer of the pin vertex group work.

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  • $\begingroup$ Wow: service with a smile. How it manged to get the Vertex Group vertices as Point Float Values, is a bit mystifying to me. Thanks so very mucho! On to adujstments and adding forces to make the simulation more interesting... $\endgroup$
    – james_t
    Mar 8, 2022 at 20:29

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