Generalize export functions and make them public

[IamTheCarl]

Exposes export functions for specific mesh formats and generalizes them to write to objects that implement Write (except for 3MF which needs the target to implement both Write and Seek).

[hannobraun]

Thank you, @IamTheCarl, looks good!

except for 3MF which needs the target to implement both Write and Seek

I wonder why that is, and if that's a real requirement. Maybe it's just a weird leftover from an earlier version. Don't know!

[IamTheCarl]

I wondered that too so I gave the source code a quick peruse (I would have updated the ThreeMF library if it looked like an easy fix)

ThreeMF uses the Zip crate to produce the 3MF file.
ZipWriter expects an object that is both Write and Seek
ZipWriter uses the seek functionality of the writer multiple times during the finalization process.

This isn't a big problem for me though. I can just output the 3MF to a tempfile before I send it to stdout, in the rare case that someone wants to pipe a 3MF file to stdout. The only situation I can see that being useful in is if someone wanted to automatically pipe a model into a slicer without an intermediate file to clean up later, which is actually something I can see myself doing.

[hannobraun]

That makes sense. Thank you for looking into it!

This isn't a big problem for me though. I can just output the 3MF to a tempfile before I send it to stdout, in the rare case that someone wants to pipe a 3MF file to stdout. The only situation I can see that being useful in is if someone wanted to automatically pipe a model into a slicer without an intermediate file to clean up later, which is actually something I can see myself doing.

You actually don't need to go through a file. You can use Cursor to do everything in-memory.

[IamTheCarl]

I did consider that but my concern is how much memory do I need? I'm probably being paranoid (thanks to my embedded background) but a spooled temp file is the best of both worlds and easy to use: https://docs.rs/tempfile/3.10.1/tempfile/struct.SpooledTempFile.html

[hannobraun]

Ah, okay. I just mentioned it in case you're not aware. SpooledTempFile seems like a safe bet.