Using Transient graphics

By Balaji Ramamoorthy

In this post we looked at using graphics functions provided by AutoCAD API to show temporary graphics. In this post we will look at using the transient graphics API to draw temporary graphics. This API provides us much better control over the display of the graphics as compared to the graphics functions.

Here is a sample code that uses transient graphics to mark the intersection points of rectangle and a ray. To try this, draw a rectangle and select an internal point and the ray direction when prompted.

Using ObjectARX :

static AcArray _markers;
static AcArray viewportNumbers;
 
static void ArxProject_Test(void)
{
    Acad::ErrorStatus es;
    AcDbDatabase *pDb = 
        acdbHostApplicationServices()->workingDatabase();
 
    ads_point pickPnt;
    ads_name ent_name;
    int ret = acedEntSel(
                            ACRX_T("n Select a polylinen"),
                            ent_name, 
                            pickPnt
                        );
    if(ret != RTNORM)
        return;
 
    AcDbObjectId plOid;
    es = acdbGetObjectId(plOid, ent_name);
    if (es != Acad::eOk)
        return;
 
    ads_point adsTestPoint;
    ret = acedGetPoint 
                (
                    NULL, 
                    ACRX_T("n Select an internal pointn"), 
                    adsTestPoint
                ) ;
    if(ret != RTNORM)
        return;
    AcGePoint3d testPoint = asPnt3d(adsTestPoint);
 
    ads_real rayAngle = 0.0;
    ret = acedGetAngle(
                        asDblArray(testPoint), 
                        ACRX_T("Specify ray direction"), 
                        &rayAngle
                      );
    if(ret != RTNORM)
        return;
 
    AcGePoint3d tempPoint = testPoint + AcGeVector3d::kXAxis;
    tempPoint = tempPoint.rotateBy(
                                    rayAngle, 
                                    AcGeVector3d::kZAxis, 
                                    testPoint
                                  );
    AcGeVector3d rayDir = tempPoint - testPoint;
 
    ClearTransientGraphics();
 
    AcDbTransactionManager* pTM = pDb->transactionManager();
    AcTransaction *pTransaction = pTM->startTransaction(); 
    AcDbObject *pCurveObj = NULL;
 
    es = pTransaction->getObject(
                                    pCurveObj, 
                                    plOid, 
                                    AcDb::kForRead
                                );
    AcDbCurve *pCurve = AcDbCurve::cast(pCurveObj);
 
    AcGiTransientManager* pTransientManager 
                                = acgiGetTransientManager();
 
    viewportNumbers.removeAll(); 
    struct resbuf res;
    acedGetVar(L"CVPORT", &res); 
    viewportNumbers.append(res.resval.rint);
 
    if(pCurve != NULL)
    {
        for (int cnt = 0; cnt < 2; cnt++)
        {
            if (cnt == 1)
                rayDir = rayDir.negate();
 
            AcDbRay ray;
            ray.setBasePoint(testPoint);
            ray.setUnitDir(rayDir);
 
            AcGePoint3dArray IntersectionPoints;
            es = pCurve->intersectWith(
                                        &ray, 
                                        AcDb::kOnBothOperands, 
                                        IntersectionPoints
                                      );
            if(es == Acad::eOk)
            {
                int numberOfInters = 0;
                numberOfInters = IntersectionPoints.length();
                for(int i=0; i < numberOfInters; ++i)
                {
                    AcGePoint3d pt = IntersectionPoints[i];
                    AcDbCircle *marker 
                        = new AcDbCircle
                                    (
                                        pt, 
                                        AcGeVector3d::kZAxis, 
                                        0.2
                                    );
                    AcCmColor color;
                    color.setColor(2);
                    marker->setColor(color);
                    _markers.append(marker);
 
                    pTransientManager->addTransient
                                        (
                                            marker, 
                                            kAcGiDirectShortTerm, 
                                            0, 
                                            viewportNumbers
                                        );
 
                    acutPrintf(
                                ACRX_T("n Point : %lf %lf"), 
                                pt.x, 
                                pt.y
                              );
                }
            }
        }
    }
    pTM->endTransaction(); 
}
 
static void ClearTransientGraphics()
{
    AcGiTransientManager* pTransientManager 
                                    = acgiGetTransientManager();
 
    int numOfMarkers = _markers.length();
    if (numOfMarkers > 0)
    {
        for(int index = 0; index < numOfMarkers; index++)
        {
            AcDbEntity *pMarker = _markers.at(index);
            pTransientManager->eraseTransient
                                    (
                                        pMarker, 
                                        viewportNumbers
                                    );
            delete pMarker;
        }
        _markers.removeAll(); 
    }
}

Using AutoCAD .Net API :

using Autodesk.AutoCAD.GraphicsInterface;
 
DBObjectCollection _markers = null;
 
[CommandMethod("Test")]
public void TestMethod()
{
    Document activeDoc 
        = Application.DocumentManager.MdiActiveDocument;
    Database db = activeDoc.Database;
    Editor ed = activeDoc.Editor;
 
    PromptEntityOptions peo 
        = new PromptEntityOptions("Select a polyline : ");
    peo.SetRejectMessage("Not a polyline");
    peo.AddAllowedClass
        (
            typeof(Autodesk.AutoCAD.DatabaseServices.Polyline),
            true
        );
    PromptEntityResult per = ed.GetEntity(peo);
    if (per.Status != PromptStatus.OK)
        return;
 
    ObjectId plOid = per.ObjectId;
 
    PromptPointResult ppr =
        ed.GetPoint
        (
            new PromptPointOptions("Select an internal point : ")
        );
    if (ppr.Status != PromptStatus.OK)
        return;
    Point3d testPoint = ppr.Value;
 
    PromptAngleOptions pao
        = new PromptAngleOptions("Specify ray direction");
    pao.BasePoint = testPoint;
    pao.UseBasePoint = true;
    PromptDoubleResult rayAngle = ed.GetAngle(pao);
    if (rayAngle.Status != PromptStatus.OK)
        return;
 
    Point3d tempPoint = testPoint.Add(Vector3d.XAxis);
    tempPoint 
        = tempPoint.RotateBy(
                                rayAngle.Value, 
                                Vector3d.ZAxis, 
                                testPoint
                            );
    Vector3d rayDir = tempPoint - testPoint;
 
    ClearTransientGraphics();
    _markers = new DBObjectCollection();
 
    using (Transaction tr 
                = db.TransactionManager.StartTransaction())
    {
        Curve plcurve = tr.GetObject(
                                        plOid, 
                                        OpenMode.ForRead
                                    ) as Curve;
 
        for (int cnt = 0; cnt < 2; cnt++)
        {
            if (cnt == 1)
                rayDir = rayDir.Negate();
 
            using (Ray ray = new Ray())
            {
                ray.BasePoint = testPoint;
                ray.UnitDir = rayDir;
 
                Point3dCollection intersectionPts 
                                    = new Point3dCollection();
                plcurve.IntersectWith(
                                        ray, 
                                        Intersect.OnBothOperands, 
                                        intersectionPts, 
                                        IntPtr.Zero, 
                                        IntPtr.Zero
                                     );
 
                foreach (Point3d pt in intersectionPts)
                {
                    Circle marker 
                        = new Circle(pt, Vector3d.ZAxis, 0.2);
                    marker.Color = Color.FromRgb(0, 255, 0);
                    _markers.Add(marker);
 
                    IntegerCollection intCol 
                                    = new IntegerCollection();
                    TransientManager tm 
                        = TransientManager.CurrentTransientManager;
 
                    tm.AddTransient
                        (
                            marker,
                            TransientDrawingMode.Highlight,
                            128, 
                            intCol
                        );
 
                    ed.WriteMessage("n" + pt.ToString());
                }
            }
        }
        tr.Commit();
    }
}
 
void ClearTransientGraphics()
{
    TransientManager tm
            = TransientManager.CurrentTransientManager;
    IntegerCollection intCol = new IntegerCollection();
    if (_markers != null)
    {
        foreach (DBObject marker in _markers)
        {
            tm.EraseTransient(
                                marker,
                                intCol
                             );
            marker.Dispose();
        }
    }
}