Temporary graphics in AutoCAD

By Balaji Ramamoorthy

It usually helps to visually see the results of our geometric computations. ObjectARX and the AutoCAD .Net API provide a few temporary graphics methods that come very handy in such scenario.

One way to do this is to use the transient graphics API, but in this post I will introduce you to yet another way - the usage of the low level graphics methods such as "acedGrVecs" and its .Net equivalent "DrawVectors".

Here is a sample code that draws a vector and its mirror about the X axis. A "zoom" or "regen" will erase the temporary graphics. As mentioned in the ObjectARX documentation, since these methods rely on the graphics system, there can be some change in its behavior between AutoCAD releases. Please ensure that you test your application with all the AutoCAD releases that you expect your application to work with.

Here is the ObjectARX version :

ads_point fromPt;

int rc = acedGetPoint(NULL, _T("\nPick first point"), fromPt);

if(rc != RTNORM)

    return;

 

ads_point toPt;

rc = acedGetPoint(NULL, _T("\nPick second point"), toPt);

if(rc != RTNORM)

    return;

 

int colorIndex = 2;

 

// Compute the mirror vector

ads_point fromPtMirror;

ads_point_set(fromPt, fromPtMirror);

fromPtMirror[1] *= -1.0;

 

ads_point toPtMirror;

ads_point_set(toPt, toPtMirror);

toPtMirror[1] *= -1.0;

 

struct resbuf  *vlist;

 

// Build ResBuf

vlist = acutBuildList(   

                    RTSHORT, colorIndex,   // Color

 

                    RTPOINT, fromPt,       // Actual vector

                    RTPOINT, toPt,

 

                    RTPOINT, fromPtMirror, // Mirror vector

                    RTPOINT, toPtMirror,

 

                    RTNONE);

 

// Using aced method to create temporary graphics.

// NULL for identity transformation matrix

rc = acedGrVecs(vlist, NULL);

 

// Cleanup

acutRelRb(vlist);

Here is the equivalent of the above code using the AutoCAD .Net API :

private const int RTPOINT = 5002;

private const int RTSHORT = 5003;

Document activeDoc =

            Application.DocumentManager.MdiActiveDocument;

Editor ed = activeDoc.Editor;

 

PromptPointResult ppr1 = ed.GetPoint("\nPick first point");

if (ppr1.Status != PromptStatus.OK)

    return;

 

PromptPointResult ppr2 = ed.GetPoint("\nPick second point");

if (ppr2.Status != PromptStatus.OK)

    return;

 

Point3d sp = ppr1.Value;

Point3d ep = ppr2.Value;

 

int colorIndex = 1;

 

using (ResultBuffer resBuf = new ResultBuffer())

{

    resBuf.Add(new TypedValue(RTSHORT, colorIndex));

 

    // The actual vector

    resBuf.Add(new TypedValue(

                                RTPOINT,

                                new Point2d(sp.X, sp.Y)

                             )

               );

 

    resBuf.Add(new TypedValue(

                                RTPOINT,

                                new Point2d(ep.X, ep.Y)

                             )

               );

 

    // and its mirror about x axis

    resBuf.Add (new TypedValue(

                                RTPOINT,

                                new Point2d(sp.X, -sp.Y)

                              )

               );

 

    resBuf.Add(new TypedValue(

                                RTPOINT,

                                new Point2d(ep.X, -ep.Y)

                              )

               );

 

    ed.DrawVectors(resBuf, Matrix3d.Identity);

}