155 provide example for the material mapping

[ClemensLinnhoff]

Describe your changes

• Add example glTF file showcasing both mesh-based and texture-based material assignment
• Adjust material examples, mapping table, asset file etc. to fit to this example
• Add Readme to explain the examples

Issue ticket number and link

Fixes #155

Checklist before requesting a review

• I have performed a self-review of my code/documentation.
• My changes generate no new warnings during the documentation generation.

[ClemensLinnhoff]

@MatthiasThDs @ipg-jsc @ipg-sig @lyndyRott please also feel free to review this.

[AsamDiegoSanchez]

General review
Signed-off-by: Diego Sánchez [email protected]

[lyndyRott]

looks like a good example to me. From the checker_xom.png (referring to red and blue material definitions) and the color-channels provided in the mapping table (referring to black and white texture names with red and blue rgb-values) it could be confusing to understand the mapping, if the chosen color values are mixed channel. Nevertheless, I can understand that these are the chosen IDs for the material mapping.

[ClemensLinnhoff]

looks like a good example to me. From the checker_xom.png (referring to red and blue material definitions) and the color-channels provided in the mapping table (referring to black and white texture names with red and blue rgb-values) it could be confusing to understand the mapping, if the chosen color values are mixed channel. Nevertheless, I can understand that these are the chosen IDs for the material mapping.

Thanks for your review. I can see how this might be confusing. But I actually deliberately chose other colors than black and white for the assignment texture to showcase, that these are just arbitrary mapping IDs and not the actual colors of the visual texture. I think we need to make this very clear in the documentation about the assignment/mapping.

[KimuraDIVP]

I think we'd better add the discription about assigning Matrial Mapping File (example_mapping.xomm) to Asset File (example_asset.xoma).

[ClemensLinnhoff]

I think we'd better add the discription about assigning Matrial Mapping File (example_mapping.xomm) to Asset File (example_asset.xoma).

You are right, thanks for the remark. I somehow missed that.
I added it now as "materialMappingUri".

[LudwigFriedmann]

Very cool example! I was about to suggest adding an object with global material parameters in parallel to the textured cube, until I found the sphere in the code :)

[MatthiasThDs]

hey @ClemensLinnhoff i am wondering if we should limit ourself to RGB values here. 24 Bit, 16 Mio values enough for all kinds of MaterialIDs.
I think that the alpha value could be useful for something we plan in OpenMaterial 2.0. But if people now already use the alpha channel for IDs, then its hard to change.
My idea here would be to reserve the alpha channel for the future. Maybe for layered Materials.

[MatthiasThDs]

Regarding this: we may also want to clarify, that the MaterialID Textures need to be 32Bit RGBA.
or do we want to support 24Bit RGB as well?

[MatthiasThDs]

I think we are missing the link to the XOMM file, from the XOMA file.
Something like "materialMapping" : "example_mapping.xomm"