OccWrapper

How to compile

First, you will need to install a version of OpenCASCADE and pybind11. OpenCASCADE is a HUGE dependency, but it's also what we're wrapping, so there's no getting around it. pybind11 is pretty small.

# you need the sub-projects if you want to build the tests
git clone --recurse-subprojects https://github.com/ezzieyguywuf/OccWrapper
cd OccWrapper
mkdir build
cd build
cmake ..
make -j8 all
make test # if you want to run the tests

What is it?

OccWrapper is intended to be used as an abstraction layer for OpenCasCade (see? OCC?). It is being written specifically with FreeCAD in mind, but should work just as well for any other project that wishes to use the functionalities of OpenCasCade.

Why?

OpenCasCade is a great library, and provides lot's of features to its users. Unfortunately, it is also a very old code base, with lots of legacy code and classes, many of which are obsolete and have been replaced with new (better?) options. The old stuff has been kept around for backwards compatibility (I guess).

Aside from that, OpenCasCade can also be a bit bearish to work with at times. Say you have a TopoDS_Solid, let's call it mySolid. How does one figure out how many faces are in mySolid? I guess:

TopoDS_Solid mySolid = GetMySolid(); // get it from wherever
// create a container for the faces;
TopTools_IndexedMapOfShapes faces;
// fill the container
TopExp::Explorer(mySolid, TopAbs_FACE, faces);
// Get the number of faces
std::cout << "mySolid has " << faces.Extent()
          << " faces" << std::endl;
// how do we iterate this?
for (int i=1; i<= faces.Extent() ; i++)
{
    TopoDS_Face aFace = faces.FindKey(i);
}

"Oh, that wasn't so painful" you might be thinking. And I guess you'd be right. But what about if I just performed a boolean fusion using a BRepAlgoAPI_Fuse object, let's call it mkFuse, and I want to retrieve a list of the faces which, say, the first face in mySolid was modified to? hrm, not so easy...

BRepAlgoAPI_Fuse mkFuse(mySolid, myOtherSolid);
mkFuse.Build()
// so, we still need a list of our faces...
TopTools_IndexedMapOfShapes faces;
TopExp::Explorer(mySolid, TopAbs_FACE, faces);
// except, the return value of mkFuse.Modified is not a TopTools_IndexedMapOfShapes...
TopTools_ListOfShape modified = mkFuse.Modified(faces.FindKey(1));
// now, how do we access these modified faces again?
TopTools_ListIteratorOfListOfShape it(modifie);
for(; it.More(); it.Next())
{
    TopoDS_Face aFace = it.Current();
}

Man. This is confusing. I have different container types, one of them has a helper iterator class, and honestly I just can't keep it all straight. This was the primary impetus for OccWrapper, literally because I couldn't keep this all straight. Here's how you would perform these same tasks using OccWrapper:

TopoDS_Solid mySolid = GetMySolid()
Occ::Solid myOccSolid(mySolid);
// Get the number of faces
std::cout << "mySolid has " << myOccSolid.getFaces().size()
          << " faces" << std::endl;
// getFaces returns a std::vector so...
for (const Occ::Face& aFace : myOccSolid.getFaces())
{
    // do something with aFace
}

What about the whole mkFuse.Modified thing? Well, we have a wrapper for that:

BRepAlgoAPI_Fuse mkFuse(mySolid, myOtherSolid);
Occ::BooleanSolid myFusion = Occ::SolidMaker::MakeBoolean(mkFuse);
const Occ::ModifiedSolid& myModifiedSolid = myFusion.getModifiedSolids()[0];
// getModifiedFaceIndices returns a vector of unsigned ints, so...
for (uint i : myModifiedSolid.getModifiedFaceIndices(mySolid.getFaces()[0])))
{
    const Occ::Face aFace = mySolid.getFaces()[i];
    // do something with aFace
}

Why does getModifiedFaceIndices return a vector if int instead of a vector of Occ::Face? Because, in my use cases (i.e. in TopoManagers) I needed the indices more often than I needed the faces themselves.

Project Status

The project is in its infancy. It is barely started. I don't even have an Occ::Vertex wrapper. At this point, it is mostly a proof-of-concept to show how an OpenCasCade wrapper could be used in order to make working with occ less painful. It has also been used in the development of the TopoManagers library.

TODO

• eliminate all the stored vectors and just used TopExp::MapShapes or w/e each time someone calls getFaces or getEdges.
• Add Occ::Vertx
• to be continued...