The Transfer UVs tool - found in the Tools section of the main DECALmachine panel - can be used to manually match decals to their parent object's textured materials, IF those materials use UVed image textures directly connected to a Principled BSDF node.
If your parent object's material uses generated coordinates, you can use the Init Generated Coords
Transfer UVs does three things:
- Create second UV Channel for the decal mesh
- Transfer the decal parent's UVs to the decal
- Copy the image textures used in the parent's material to the decal material and link them to the decal node group.
Keep in mind
The tool optionally supports using the parent material's normal map, as well as use parallax on the transfered textures.
However for both of these to properly work, the UV spaces of decal and parent object have to be oriented in the same way, which will almost never be the case in real world scenarios.
One or multiple Decal objects in object mode
Default: Transfer UVs and Image Textures
ALT: Remove/Undo UV Transfer