MJCF to SDF: Add Material

[ahcorde]

Signed-off-by: ahcorde ahcorde@gmail.com

🎉 New feature

Summary

Add Material

I have two issues:

• file name are changed, we used in the mjcf file file.png and we got from the python API file-hash.png, should I create this file ? add a flag to export them ?
• According with XML Reference, tight now we only support gridsize="1 1". There is other way to define textures, please review this field gridlayout: string, “…………” and share your thoughts. This way is not defined ignition, this may require some work in other ignition libraries

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #42 (e19d5a2) into main (7faaf8d) will decrease coverage by 0.33%.
The diff coverage is 92.15%.

@@            Coverage Diff             @@
##             main      #42      +/-   ##
==========================================
- Coverage   97.54%   97.20%   -0.34%     
==========================================
  Files          18       19       +1     
  Lines         773      824      +51     
==========================================
+ Hits          754      801      +47     
- Misses         19       23       +4     

Impacted Files	Coverage Δ
...o_sdformat/mjcf_to_sdformat/converters/material.py	91.48% <91.48%> (ø)
...cf_to_sdformat/mjcf_to_sdformat/converters/link.py	100.00% <100.00%> (ø)

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[azeey]

According with XML Reference, tight now we only support gridsize="1 1". There is other way to define textures, please review this field gridlayout: string, “…………” and share your thoughts. This way is not defined ignition, this may require some work in other ignition libraries

I have created an issue about the difference in texture mapping between Gazebo and Mujoco for primitive shapes (#58). I want to test how it works with meshes as well, but we don't have mesh conversion yet. I think it's safe to say SDFormat doesn't support gridlayout, so we can just emit an warning/error if we see a file with that attribute.

[azeey]

I don't think we should be setting the emissive property based on the rgba, but I don't have a good suggestion. Maybe we can come back to it later.