ACIS parser contribution

[JMLX42]

Hello!

There is a GPL-2 ACIS parser developed in Python for FreedCAD here:

https://github.com/jmplonka/InventorLoader

Especially this file:

https://github.com/jmplonka/InventorLoader/blob/master/Acis.py

Since I need ACIS parsing in C/C++, I'm going to attempt to port this to C/C++.
And since it is my understanding that DWG files might contain ACIS data, it might probably be better to use C.
Still, I was wondering what would be the best course of action project wise:

• A separate ACIS parsing library that libredwg might leverage
• A pull request to add ACIS parsing to libredwg

Please let me know.

Related issues:

• Is it possible to give the windows project file?  #25
• How tessellate 3D data? #270
• Getting error while trying to convert dwg to json #200

[rurban]

We already do parse ACIS by our own, in C. For both ACIS types, the old official, and the new extended format with history. Should be easy to find. I also log the decrypted ACIS for each object, if stored in the object or linked into the seperate AcDs section.

I didnt know about this python lib, looks great. Would have helped, because I've reverse engineered the new undocumented format by my own. Would need to crosscheck, what they have and what I have.

[JMLX42]

We already do parse ACIS by our own, in C. For both ACIS types, the old official, and the new extended format with history. Should be easy to find. I also log the decrypted ACIS for each object, if stored in the object or linked into the seperate AcDs section.

I have missed that in the code then. I'm relying a lot on dwg2svg.c. Is it supposed to be parsed there?

Is the ACIS inspected by ./log too?

I didnt know about this python lib, looks great. Would have helped, because I've reverse engineered the new undocumented format by my own. Would need to crosscheck, what they have and what I have.

So basically the short answer is: no ACIS parser needed. Correct?

[rurban]

Correct. The function is in out_dxf.c. There are two formats. The old is just decrypted to ASCII SAT, the new one is a binary SAT with Autodesk extensions, which can be stored elsewhere, not with the object.
All those fields are printed with log, ie dwgread -v3 or also exported to json.

/* Converts v2 SAB acis_data in-place to SAT v1 encr_sat_data[].
   Sets dxf_sab_converted to 1, denoting that encr_sat_data is NOT the
   encrypted acis_data anymore, rather the converted from SAB for DXF.
*/
EXPORT int
dwg_convert_SAB_to_SAT1 (Dwg_Entity_3DSOLID *restrict _obj)

[JMLX42]

Correct. The function is in out_dxf.c. There are two formats. The old is just decrypted to ASCII SAT, the new one is a binary SAT with Autodesk extensions, which can be stored elsewhere, not with the object.
All those fields are printed with log, ie dwgread -v3 or also exported to json.

Thank you!

But I'm afraid I might be missing the important part again. LibreDWG does provides:

• Decrypted ACIS SAT data (ASCII 3D geometry description)
• Pre-parsed wireframe representation (wires array)
• Conversion from SAB (binary) to SAT (ASCII) format

But libredwg does not parse the SAT format to extract full solid geometry (faces, surfaces, topology).

Correct?

[rurban]

Yes, we leave that to you. That's too hard, and we dont need it. But the topology is easy to see in SAT format

[JMLX42]

Closed in favor of #1160