What is ObjectARX?
ObjectARX is a C++ SDK that runs inside the AutoCAD process with direct access to the drawing database and core services. Applications are compiled as .arx (application) and .dbx (object enabler) modules.
What only ObjectARX does well
| Capability | Why it matters |
|---|---|
| Custom entities | New object types with their own drawing, grips, snaps and data (for example a "smart valve" or "beam") |
| Object enablers | Let other users open and view drawings with your custom objects |
| Maximum performance | Native code for heavy geometry or very large drawings |
| Deep integration | Low-level reactors, protocol extensions, custom file handling |
| Reuse of C++ libraries | Engineering calculation engines and geometry kernels |
Custom entity example
class EmPipe : public AcDbEntity
{
public:
ACRX_DECLARE_MEMBERS(EmPipe);
Acad::ErrorStatus dwgInFields(AcDbDwgFiler* filer) override;
Acad::ErrorStatus dwgOutFields(AcDbDwgFiler* filer) const override;
Adesk::Boolean subWorldDraw(AcGiWorldDraw* wd) override;
Acad::ErrorStatus subGetGripPoints(AcGePoint3dArray& grips,
AcDbIntArray& osnapModes, AcDbIntArray& geomIds) const override;
private:
AcGePoint3d m_start, m_end;
double m_diameter = 100.0;
AcString m_spec; // pipe specification
};Custom entities vs overrules
Custom entities need an object enabler to display correctly for others. Overrules (available in both ObjectARX and .NET) change how standard entities look or behave without creating new types, which avoids proxy objects. Choosing the right approach is an important design decision.
Version compatibility
- ObjectARX modules must be built with the Visual Studio version specified for each AutoCAD release family.
- Binary compatibility usually spans a few releases, then a rebuild is required.
- Custom object data formats must be versioned to stay readable.
When to choose ObjectARX
- You need true custom objects.
- Performance matters on very large data sets.
- You are building a commercial product on AutoCAD.
- You have existing C++ engineering code to reuse.
For most business add-ins, .NET is faster to develop. Many products combine both: ObjectARX for the core objects and .NET for the user interface.
Use ObjectARX where its power is needed, and .NET everywhere else.
ObjectARX development with ENGIMANDI
See AutoCAD API development and our comparison of AutoLISP vs .NET vs ObjectARX.