Hi Leonard - when you project a curve on to a surface, it creates a new curve object, the surface itself is not modified in any way yet. The curve hugs the surface but it is totally separate from it at this point, for example you can just drag it off to the side and see that your original surface is there untouched.
If you want to have separate colors for different areas of a surface, you'll need to actually cut the surface up to make it into separate independent pieces that can then have individual properties assigned to them.
You can use the Trim command for that using the projected curve to slice the top of the button, or like you already showed doing a Boolean Merge using the original planar object without doing any separate projection will work for that.
> Without the id for each part, the parts are merged
> back into a single object (pic below).
They don't have to be - there is a setting for that which you can turn off. Go to Options > Import/Export and uncheck the option that says "Combine same named objects" here:
Then when you export after that, you should see that the objects are individually selectable inside of Cinema4D, even though they have the same name label assigned to them.
There are some other ways you can do it as well - in your case the objects are being combined because they have the same name label, so if you assign a different name label to each piece (or removed the name labels altogether by giving them blank names) they would then not be combined even with that setting turned on.
You can also do Style assignments as well, which will then control material assignments of the different polygons in Cinema4D. That allows you to set up different colors on different parts of an object without necessarily needing to make it into separate top-level objects.
For example if you make a box, and set the sides to have Style = Red, and the top face to have Style = Blue in MoI, then when you export that to OBJ format and bring it into Cinema4D there will be some materials named "Red" and "Blue" in the materials list there, and the polygons will be assigned to each of those. So you don't need to select or assign any materials in that case, that's all done already and you can just edit the materials to change the way they look. You may want to use the Riptide plugin for this since it brings in the material colors which the default Cinema4D OBJ importer does not do (but the default one will still maintain assignments though).
- Michael