DWG support enhancement

I'm working on DWG support in my branch:

https://github.com/dxli/LibreCAD/tree/dwg

Rallaz started dwg support in dxfrw quite many years ago. While the dxfrw library was designed to allow easy addition of DWG support, the supported DWG features were only implemented at a preliminary level.

As my current work is mostly limited to completion of placeholders of missing DWG features, so I chose to directly work in the LibreCAD repository, instead of the official libdxfrw repository. Ideally, the new additions to dxfrw in LibreCAD will be ported to the libdxfrw later on.

The dwg branch is expected to be merged in the coming days.

To help resolving DWG loading issues, please submit minimum sample dwg files as issues at our github LibreCAD page.

https://github.com/LibreCAD/LibreCAD/issues

It’s certainly welcome news that DWG support is improving, and I’m grateful for it.
Although I don’t know much about the detailed technical aspects, I understand that DWG is Autodesk’s proprietary, closed file format, which makes it difficult for software like LibreCAD to freely use it (open, edit, save, etc.).
I’ve long been curious about how other CAD programs—sold at relatively lower prices by software companies outside Autodesk in various countries—are able to handle this proprietary DWG file.
And from a user’s perspective, I also wonder how tools like the ODA converter or LibreCAD manage to deal with this secretive DWG format.

DWG is not actually secretive.

Several layers:

1, as a file format, there's no law against creating a software to read the dwg file format;
2, while the format itself is proprietary, the open design alliance has published a reverse engineered specification for dwg:
https://www.opendesign.com/files/guestdownloads/OpenDesign_Specification_for_.dwg_files.pdf
3, dwg itself stands for the file format, and is not considered a trademark here;
4, LibreDWG has been developed by FSF for many years, but LibreCAD cannot directly use LibreDWG, due to license compatability issues;
5, because of item 4, LibreCAD developer Rallaz started to add DWG support in the dxfrw library, which is part of LibreCAD.

Urstein wrote

It’s certainly welcome news that DWG support is improving, and I’m grateful for it.
Although I don’t know much about the detailed technical aspects, I understand that DWG is Autodesk’s proprietary, closed file format, which makes it difficult for software like LibreCAD to freely use it (open, edit, save, etc.).
I’ve long been curious about how other CAD programs—sold at relatively lower prices by software companies outside Autodesk in various countries—are able to handle this proprietary DWG file.
And from a user’s perspective, I also wonder how tools like the ODA converter or LibreCAD manage to deal with this secretive DWG format.