Rotate texture per instance

Question

I'm trying to get this wood texture mapped correctly according to the rotation of the objects. In an ideal situation, the textures all align so they point to the middle of the cirle. I have loads of products to render, where unwrapping/rotating the texture on each beam is not an option. I'm importing these from solidworks using .WRL format. This makes it more difficult, because the rotation in blender is 0 degrees on every axis..

So the question is, how would i make a mapping nodegroup that maps the (pbr)textures on each instance according to the rotation of the object (imported from SW). Is this possible entirely in shader nodes, or do i need a geometrynode component aswell?

Thanks in advance!

edit: I think i have not explained my situation well enough. The beams are 3d objects with bevels on it and have rough topology.

Answer 1

Solution for individual objects - volumetric - bad topology

This solution requires that you set the origins of the objects to the center of the circle. (You do that by placing the 3d cursor at the center - shift + right click, then select all objects, right click, set origin, origin to 3d cursor)

Use this to copy material to all objects: Copy material to another object? (where the "special" in newer blenders is a "down arrow")

(the same principle for copying apply to geometry nodes, in blender 4.2, you click the down arrow on the material or the modifier)

Geometry nodes

• Calculates the mean position of the faces
• Calculates a provisory vector from the origin (center) to the mean position, discarding Z (provisory local X)
• Uses maths to create local X and local Y for each face based on this provisory X

Shader nodes

Gets the local X and Y and calculate the position of the geometry in this local coordinate system

Result for volumetric objects with bad topology

For flat (2d) objects with good topology

Geometry nodes

These store a X axis for the texture.

• It needs tiles with 4 edges
• It takes the two smallest edges and calculate X based on the center of these edges
• It stores the normalized X axis in a named attribute (important: store as vector)

Shader nodes

• Take the Texture X axis
• Calculates the Texture Y axis by cross product Normal x X
• Calculates the position of the geometry in the new texture coordinate system (dot products)

(The wave texture represents your wood texture)

PS: you might need to rescale the texture, in this case, add a multiply or a vector map right before the texture.

Result

Solution for mesh islands

Here, you have a single object instead of many individual objects.

• This requires that all islands have 4 vertices!!

Solution for volumetric objects with good topology (faces = quads)

Here, we extrapolate the previous island solution.

• Split the edges to make every individual face its own UV island
• Store the X axis for each face
• Join the geometry together again (merge by distance)