Multimaterial does not support walls with multiple widths

[furgo16]

Is there an existing issue for this?

• I have searched the existing issues

Problem description

A common use case for exterior walls with multiple widths are older houses (e.g. one century in the past). Exterior walls with multiple widths can be created from individual walls grouped within a parent wall.

When applying a multimaterial to walls created like this, the materials are not displayed correctly. One material's color seem to take over the whole component, and the lines dividing materials are not properly rendered.

See the attached example, where a multimaterial was created for each wall width.

Full version info

OS: Ubuntu Core 22 (ubuntu:GNOME/ubuntu)
Word size of FreeCAD: 64-bit
Version: 0.22.0dev.37213 (Git) Snap 1010
Build type: Release
Branch: main
Hash: 20e7deb86a8c6c2cd2378f09f8313760933f3a5c
Python 3.10.12, Qt 5.15.10, Coin 4.0.0, Vtk 7.1.1, OCC 7.7.1
Installed mods: 
  * OpenTheme 2024.4.20
  * BIM 2021.12.0
  * Curves 0.6.35
  * ezydxf
  * ExplodedAssembly
  * BillOfMaterials 0.0.8.2
  * Ondsel-Lens 2024.4.16.01
  * Assembly4 0.50.12

Subproject(s) affected?

Arch

Anything else?

Multiwalls multimaterial.zip

Code of Conduct

• I agree to follow this project's Code of Conduct

[yorikvanhavre]

Indeed, good point.

Joining walls under a "host" wall is not designed to make multilayer walls. Therefore it takes the geometry of the child walls and joins it to the main wall. In fact it becomes one wall.

But creating multilayer walls that way is indeed very interesting. It offers much more flexibility over multilayer walls made with multimaterials. We should support this. In fact, tools like Windows already support it, they will propagate their holes to all "sibling" walls (ie. walls that share the same baseline).

What we need here is:

• A way to differentiate wall layers from wall additions. Currently layers added to a host wall are treated as additions, and therefore fused. Maybe a different property?
• Multimaterials applied to the host wall should be correctly distributed to layers. But how to know which layer wall must receive which submaterial?