Overruling Osnaps of BlockReference

By Balaji Ramamoorthy

When overruling the osnap points for a BlockReference, you may not want the osnap points of the entities that make the Block reference from getting snapped. For this, override the “IsContentSnappable” method of the “OsnapOverrule” class.

Here is a sample code to add the center point of the BlockReference as a osnap point and prevent all other osnap points, including those of the entities that make the BlockReference.

using System.Collections.Generic;
 
public class ExtApp : IExtensionApplication
{
    static ObjectSnapOverrule m_osnapOverrule 
                                    = new ObjectSnapOverrule();
    static Overrule[] m_overrules = new Overrule[]
    {
        m_osnapOverrule,
    };
    static List m_overruledObjects = new List();
    static bool m_overruleAdded = false;
 
    [CommandMethod("startOverrule")]
    static public void Start()
    {
        Document doc = Application.DocumentManager.MdiActiveDocument;
        Editor ed = doc.Editor;
 
        PromptEntityOptions peo = new PromptEntityOptions(
                        "Select a blockreference to overrule :"
                       );
 
        peo.SetRejectMessage("Not a block reference");
        peo.AddAllowedClass(
            typeof(Autodesk.AutoCAD.DatabaseServices.BlockReference), 
            false);
 
        PromptEntityResult per = ed.GetEntity(peo);
        if (per.Status != PromptStatus.OK)
            return;
 
        ObjectId brefId = per.ObjectId;
 
        if (!m_overruledObjects.Contains(per.ObjectId))
        {
            m_overruledObjects.Add(brefId);
        }
 
        ObjectId[] ids = m_overruledObjects.ToArray();
        foreach (Overrule o in m_overrules)
        {
            o.SetIdFilter(ids);
            if (!m_overruleAdded)
            {
                Overrule.AddOverrule(
                    RXObject.GetClass(typeof(BlockReference)), 
                    o, 
                    false);
            }
        }
 
        Overrule.Overruling = true;
        m_overruleAdded = true;
 
        Application.DocumentManager.MdiActiveDocument.Editor.Regen();
    }
 
    [CommandMethod("stopOverrule")]
    static public void End()
    {
        foreach (Overrule o in m_overrules)
        {
            Overrule.RemoveOverrule(
                RXObject.GetClass(typeof(BlockReference)), 
                o);
        }
        Overrule.Overruling = false;
        Application.DocumentManager.MdiActiveDocument.Editor.Regen();
    }
 
    void IExtensionApplication.Initialize() { }
 
    void IExtensionApplication.Terminate() { }
}
 
class ObjectSnapOverrule : OsnapOverrule
{
    public override void GetObjectSnapPoints(
                                Entity entity,
                                ObjectSnapModes snapMode,
                                IntPtr gsSelectionMark,
                                Point3d pickPoint,
                                Point3d lastPoint,
                                Matrix3d viewTransform,
                                Point3dCollection snapPoints,
                                IntegerCollection geometryIds)
    {
        BlockReference bref = entity as BlockReference;
        if (bref != null)
        {
            Database db = entity.Database;
            using (Transaction t 
                    = db.TransactionManager.StartTransaction())
            {
                BlockTableRecord btr 
                    = t.GetObject(
                                    bref.BlockTableRecord, 
                                    OpenMode.ForRead
                                 ) as BlockTableRecord;
 
                // Add only the centerpoint as snap point
                Extents3d exts = bref.GeometricExtents;
                snapPoints.Add(
                    exts.MinPoint + (exts.MaxPoint - exts.MinPoint) * 0.5);
            }
        }
    }
 
    // Return false to prevent the entities that make the 
    // block reference from getting snapped
    public override bool IsContentSnappable(Entity entity)
    {
        return false;
    }
}