In Geometry Nodes, I connect a the material socket of a 'Set Material' node to the 'Group Input' node.
Now, when the material socket in the modifier panel is empty, I want to use this fact to activate a switch node. For example, I want to trigger an 'Index Switch (material)' node to apply a different material.
How can I detect when the material socket is empty and convert that into a boolean?
If I understand correctly, you want to convert a material to boolean:
So the below overrides the material only if it's specified, otherwise uses the original material of provided geometry (and as you can see in the tooltip, this is the latter option):
Here's how I implemented this converter:
The reason it works is that any geometry created already has an empty material slot, and by setting a new material you add a material slot. I'm not sure the slot won't be overridden in the future, so you might want to create two triangles instead and only set the material on one of them (and read that triangle's material index).
To determine whether a material has been assigned via the Group Inputs, you can use the following setup:
Here I first apply the selected material to the geometry. Then I replace the selected material with an empty material.
Then I use Material Selection and Sample Index to check whether the geometry still contains the material defined at the beginning.
If not, then the slot was not empty and a new material can be assigned. If it is, then an alternative material is used.
The trick here is that if no specific material has been selected, both materials are empty when the check is done.
