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This section describes advanced functionality and techniques for extracting data from a DWG/DXF file using DWGdirectTeigha.
Dispatching on Entity Type
Applications that process entity data from a database require a means to identify each entity by its type, and perform type-specific processing on the entity. DWGdirect Teigha uses a mechanism called called protocal extension to to provide this functionality. Protocol extension allows a client application to create a new class and associate an instance of this class with a particular class of database objects. Then this new class instance may be retrieved from a generalization of the class with which it was registered, providing an effective means of dispatching by type.
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The following is the parent class for our entity dumpers:
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class OdDbEntity_Dumper : public OdRxObject
{
public:
ODRX_DECLARE_MEMBERS(OdDbEntity_Dumper);
virtual void dump(OdDbEntity* pEnt, STD(ostream) &os) const;
}; // end class OdDbEntity_Dumper
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The following defines a class for dumping OdDb2dPolyline entities. It overrides the OdDbEntity_Dumper::dump() function in order to dump the data specific to this entity.
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class OdDb2dPolyline_Dumper : public OdDbEntity_Dumper
{
public:
void dump(OdDbEntity* pEnt, STD(ostream) & os) const
{
dumpCommonData(pEnt, os);
OdDb2dPolylinePtr pPoly = pEnt;
OdDbObjectIteratorPtr pIter = pPoly->vertexIterator();
for (; !pIter->done(); pIter->step())
{
OdDb2dVertexPtr pVertex = pIter->entity();
if (pVertex.get())
{
os << " " << pVertex->isA()->name() << STD(endl);
}
}
}
}; // end class OdDb2dPolyline_Dumper
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The following function registers custom dumper classes for a number of entity types:
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void ExProtocolExtension::initialize()
{
// Register OdDbEntity_Dumper with DWGdirect
OdDbEntity_Dumper::rxInit();
m_pDumpers = new Dumpers;
m_pDumpers->addXs();
}// end ExProtocolExtension::initialize()
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And the Dumpers::addXs() functions does the following:
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void addXs()
{
OdDbEntity::desc()->addX(
OdDbEntity_Dumper::desc(), &m_entityDumper);
OdDbRegion::desc()->addX(
OdDbEntity_Dumper::desc(), &m_regionDumper);
OdDbPolyline::desc()->addX(
OdDbEntity_Dumper::desc(), &m_polylineDumper);
OdDb2dPolyline::desc()->addX(
OdDbEntity_Dumper::desc(), &m_2dPolylineDumper);
OdDb3dPolyline::desc()->addX(
OdDbEntity_Dumper::desc(), &m_3dPolylineDumper);
OdDbPolyFaceMesh::desc()->addX(
OdDbEntity_Dumper::desc(), &m_polyFaceMeshDumper);
OdDbPolygonMesh::desc()->addX(
OdDbEntity_Dumper::desc(), &m_polygonMesh);
OdDbBlockReference::desc()->addX(
OdDbEntity_Dumper::desc(), &m_blockReference);
OdDbMInsertBlock::desc()->addX(
OdDbEntity_Dumper::desc(), &m_mInsertBlock);
OdDbSpline::desc()->addX(
OdDbEntity_Dumper::desc(), &m_splineDumper);
OdDbEllipse::desc()->addX(
OdDbEntity_Dumper::desc(), &m_ellipseDumper);
OdDbSolid::desc()->addX(
OdDbEntity_Dumper::desc(), &m_solidDumper);
OdDbTrace::desc()->addX(
OdDbEntity_Dumper::desc(), &m_traceDumper);
OdDb3dSolid::desc()->addX(
OdDbEntity_Dumper::desc(), &m_3DSolidDumper);
OdDbProxyEntity::desc()->addX(
OdDbEntity_Dumper::desc(), &m_proxyEntityDumper);
OdDbHatch::desc()->addX(
OdDbEntity_Dumper::desc(), &m_hatchDumper);
OdDbCircle::desc()->addX(
OdDbEntity_Dumper::desc(), &m_circleDumper);
OdDbMText::desc()->addX(
OdDbEntity_Dumper::desc(), &m_mTextDumper);
OdDbText::desc()->addX(
OdDbEntity_Dumper::desc(), &m_textDumper);
OdDbMline::desc()->addX(
OdDbEntity_Dumper::desc(), &m_mlineDumper);
OdDbRasterImage::desc()->addX(
OdDbEntity_Dumper::desc(), &m_imageDumper);
OdDbArcAlignedText::desc()->addX(
OdDbEntity_Dumper::desc(), &m_arcAlignedTextDumper);
OdDbOle2Frame::desc()->addX(
OdDbEntity_Dumper::desc(), &m_ole2FrameDumper);
} // end addXs
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The following function retrieves the custom dispatching class associated with a particular OdDbEntity instance, and calls the virtual dump() method to display the contents of this entity.
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void DbDumper::dumpEntity(OdDbObjectId id, STD(ostream) & os)
{
// Open the entity
OdDbEntityPtr pEnt = id.safeOpenObject();
// Retrieve the registered protocol extension object registered
// for this object type.
OdSmartPtr<OdDbEntity_Dumper> pEntDumper = pEnt;
pEntDumper->dump(pEnt, os);
dumpGroupCodes(pEnt->xData(), os, " ");
if (!pEnt->extensionDictionary().isNull())
{
dumpObject(pEnt->extensionDictionary(),
"ACAD_XDICTIONARY", os, " ");
}
} // end DbDumper::dumpEntity
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The following is a protocol extension class for OdDbEntity, that uses the sample OdGiWorldGeometryDumper class to print the vector information contained in an OdEntity:
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void OdDbEntity_Dumper::dump(OdDbEntity* pEnt, STD(ostream) & os) const
{
dumpCommonData(pEnt, os);
os << " " << "Entity graphics data:" << STD(endl);
// Dump the graphics data of "unknown" entity
// graphics for proxy entity are retrieved by the same way
OdGiContextDumper ctx(pEnt->database());
OdGiWorldDrawDumper wd(os);
wd.setContext(&ctx);
pEnt->worldDraw(&wd);
} // end OdDbEntity_Dumper::dump
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