Support for materials

[adrianschneider94]

Implemented material support.
In this approach, materials are stored in python dataclasses, the OpenCascade objects are only created when building the assembly.
Tests/docs are missing at the moment.

[shimwell]

This looks great, I wonder if there is ever a use case for a material to be a string in as an option in addition to these nice material classes you have here. I was wondering if something like this would be possible / useful

assy = cq.Assembly()
assy.add(cube, name="red_cube", material="steel")

[adam-urbanczyk]

@shimwell it would certainly be nice to have some predefined materials, and maybe allow to use the material name for other things too. But let's start with making CI green.

[codecov]

Codecov Report

Attention: Patch coverage is 97.18310% with 8 lines in your changes missing coverage. Please review.

Project coverage is 95.57%. Comparing base (8c68faa) to head (a4232a0).

Files with missing lines	Patch %	Lines
cadquery/materials.py	96.47%	3 Missing and 3 partials ⚠️
cadquery/occ_impl/assembly.py	97.26%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1815      +/-   ##
==========================================
+ Coverage   95.54%   95.57%   +0.03%     
==========================================
  Files          28       29       +1     
  Lines        7319     7505     +186     
  Branches     1102     1131      +29     
==========================================
+ Hits         6993     7173     +180     
- Misses        195      198       +3     
- Partials      131      134       +3     

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[adrianschneider94]

Material support in step exporting will get better in OCCT:
Open-Cascade-SAS/OCCT#447

[adrianschneider94]

This looks great, I wonder if there is ever a use case for a material to be a string in as an option in addition to these nice material classes you have here. I was wondering if something like this would be possible / useful

assy = cq.Assembly()

assy.add(cube, name="red_cube", material="steel")

Would probably nice to have a set of materials to get started, but I think, any real-world application will require custom material sets.
Maybe there's another solution and we can find an existing material repository that can be utilized.

(edit: for example https://physicallybased.info)

[adrianschneider94]

VRML export runs, but is not correct yet.

[adrianschneider94]

The PR would be ready from my side for a first iteration.

I think it would be great to add textures later on, one could create quite good visualizations directly with cadquery/vtk. For the time, the PBR materials already achieve quite nice results.

[adam-urbanczyk]

Thanks for all the hard work! Are the new classes picklable?

[adrianschneider94]

Yes, they are pure dataclasses/basic python types, so everything can be pickled.

How far is the progress on the serialization topic? Have you thought about using pydantic? I plan to implement model caching in our internal project and json would be easier to use in a db like with Postgres' JSONB column or redis' JSON datatype compared to pickle.

[adam-urbanczyk]

Perfect, thanks!

There are no plans to implement serialization beyond pickling which is already there. For caching I'd suggest joblib, but maybe you have something else in mind.