Working with B-Reps

In Teigha you can work with solids and shells using boundary representations, or B-Reps. In different Teigha products, Teigha Drawings (for working with both .dwg and .dgn files), Teigha PRC, and Teigha BIM, there are separate implementations of B-Rep interfaces, but you can work with them using the common class OdBrBrep.

A B-Rep can be created with the help of the appropriate BrepBuilder. Builders are wrapped by the common class OdBrepBuilder just like a B-Rep.

You can fill the builder manually by calling add* functions (addFace, addEdge, etc.). Or you can get an existing B-Rep using OdBrepBuilderFillerModule.

The OdBrepBuilderFillerModule is the core extension module. It traverses a B-Rep and collects topology and material information. Then the module puts data into the builder.

To use B-Reps:

1. Add the include header:

   #include "BrepBuilderFillerModule.h"
   

2. For static builds, add a declaration of the module:

   #ifndef _TOOLKIT_IN_DLL_
   
   ODRX_DECLARE_STATIC_MODULE_ENTRY_POINT(OdBrepBuilderFillerModule);
   
   ODRX_BEGIN_STATIC_MODULE_MAP()
   ODRX_DEFINE_STATIC_APPMODULE(OdBrepBuilderFillerModuleName, OdBrepBuilderFillerModule)
   ODRX_END_STATIC_MODULE_MAP()
   
   #endif
   

3. Set up the implementation of OdBrepBuilder using the method brepBuilder of the host app service instance. For example:

   OdDbHostAppServices* pHostApp;
   …
   OdBrepBuilder builder;
   OdResult err = pHostApp->brepBuilder(builder, kOpenShell);
   if (eOk != err)
   {
     throw err;
   }
   

4. Load the module:

   OdBrepBuilderFillerModulePtr pFillerModule = ::odrxDynamicLinker()->loadModule(OdBrepBuilderFillerModuleName, false);
   

5. To handle materials, use a helper structure (its fields are optional):

   OdMaterialHelper materialHelper;
   materialHelper.pDefaultMaterial = ...;
   materialHelper.pMaterialResolver = ...;
   materialHelper.pGiContext = ...;
   

6. Because the builder does not own geometry data, you have to store this data while you use the builder:

   OdGeCurve3dPtrArray arrEdges;
   OdGeCurve2dPtrArray arrCoedges;
   OdGeSurfacePtrArray arrSurfaces;
   

7. To initialize the builder, use the method initFrom:

   OdResult err = pFillerModule->initFrom(builder, brep, arrEdges, arrCoedges, arrSurfaces, materialHelper));
   if (eOk != err)
   {
     throw err;
   }