Polyline offset using ObjectARX

By Balaji Ramamoorthy

Here is a sample code to offset a selected AcDbPolyline entity on either side of the selected polyline. The offset distance value is stored in a per-document variable. Before presenting the code to offset an AcDbPolyline, an overview of the process follows.

In offseting an existing AcDbPolyline entity, the user is asked to select an AcDbPolyline entity and the offset distance. With these parameters, “getOffsetCurves” method is used to get the offset curve.

Before trying this code, please add a variable to the DocData class which will store the value of the offset distance as explained in the code snippet.

// In DocData.h
// A public variable to store the offset distance
ads_real m_OffsetValue;

// In DocData.cpp
// Initialize the offset distance in the constructor
CDocData::CDocData () 
{
    m_OffsetValue = 1.0;
}

Here is the command implementation :

static void ADSProject_Test(void)
{
    AcDbPolyline *pPolyEnt = NULL;
    AcDbEntity *pObj;
    AcDbPolyline *pPolyPositive = NULL;
    AcDbPolyline *pPolyNegative = NULL;
    AcDbObjectId polyEntId, ownerId;
    AcDbVoidPtrArray ar_polyPositives;
    AcDbVoidPtrArray ar_polyNegatives;
 
    ads_real offset = 1.0;
    ads_name eName;
    ads_point pt;
    int rc;
 
    rc = acedEntSel(
                        ACRX_T("nSelect Polyline to offset "),
                        eName, 
                        pt
                    );
 
    if(rc != RTNORM)
    {
        acutPrintf(_T("nNothing selected "));
        return;
    }
 
    // Get the selected entity object ID
    acdbGetObjectId(polyEntId, eName);
 
    // Is the selected entity an AcDbPolyline
    acdbOpenObject(pObj, polyEntId, AcDb::kForRead);
    if(pObj == NULL)
    {
        return;
    }
 
    pPolyEnt = AcDbPolyline::cast(pObj);
    if(!pPolyEnt)
    {
        acutPrintf(_T("nNot an AcDbPolyline entity "));
        pPolyEnt->close();
        return;
    }
 
    // Now that we have a valid AcDbPolyline entity proceed
    rc = acedGetDist(
                        NULL,
                        ACRX_T("Polyline offset distance"), 
                        &offset
                    );
    switch(rc)
    {
        case RTERROR:
            acutPrintf(_T("nError with acedGetDist() "));
            pPolyEnt->close();
            return;
            break;
 
        case RTCAN:
            pPolyEnt->close();
            acutPrintf(_T("nCancelled"));
            return;
            break;
 
        case RTNONE:
            offset = DocVars.docData().m_OffsetValue;
            break;
 
        case RTNORM:
            DocVars.docData().m_OffsetValue = offset;
            break;
    }
 
    try
    {
        // who owns the polyline Model Space or Paper Space
        ownerId = pPolyEnt->ownerId();
        pPolyEnt->getOffsetCurves(offset, ar_polyPositives);
 
        //offsetPolyline(pPolyEnt, ar_polyPositives, offset);
        if(ar_polyPositives.length() != 1)
        {
            deleteArray(ar_polyPositives);
            pPolyEnt->close();
            return;
        }
        else
        {
            pPolyPositive = (AcDbPolyline*)(ar_polyPositives[0]);
            appendEntity(pPolyPositive, ownerId);
        }
 
        pPolyPositive->getOffsetCurves(
                                        -2.0 * offset, 
                                        ar_polyNegatives
                                      );
        if(ar_polyNegatives.length() != 1)
        {
            deleteArray(ar_polyNegatives);
            pObj->close();
            return;
        }
        else
        {
            pPolyNegative = (AcDbPolyline*)(ar_polyNegatives[0]);
            appendEntity(pPolyNegative, ownerId);
        }
    }
    catch(...)
    {
        acutPrintf(ACRX_T("Sorry, Error while offsetting."));
    }
 
    pPolyEnt->close();
 
    if(pPolyPositive)
    {
        pPolyPositive->close();
    }
 
    if(pPolyNegative)
    {
        pPolyNegative->close();
    }
}
 
static void deleteArray(AcDbVoidPtrArray entities)
{
    AcDbEntity* pEnt;
    int nEnts;
 
    nEnts = entities.length();
    for(int i = 0; i < nEnts; i++)
    {
        pEnt = (AcDbEntity*)(entities[i]);
        delete pEnt;
    }
}
 
static void appendEntity(
                            AcDbEntity* pEnt, 
                            AcDbObjectId recordId 
                        )
{
    AcDbBlockTableRecord* pRecord;
    acdbOpenObject(pRecord, recordId, AcDb::kForWrite);
    pRecord->appendAcDbEntity(pEnt);
    pRecord->close();
}