Moving Entity Along A Curve

I have been working much less on AutoCAD these days, thus have not posted something for quite a while.

A while ago, I was asked by one of the users of the CAD tools I developed before that if it is possible to write some code so that CAD user can drag an entity along a given path. "It surely can be done", I said to the user immediately, " but I have not tried it yet" I added. I was thinking that it can be done with a DrawJig. I did not find time write some code to materialize it until now.

The idea of doing it is fairly simple: just implementing a DrawJig, and in the Jig's Sampler() method, instead of letting the entity follow the a cursor's path during dragging, we can find a point for the entity to move to in such way that the point must be on a curve (moving path). Therefore, we need a Curve entity as our moving path.

Also, since the goal is to give user visual feedback while entity is dragged and the entity moving is only to occur after the drag (should user not cancel the dragging), I use a cloned, non-database-residing entity as the visually moving part, which is disposed when the dragging is done.

Here is the class GuidedMovingJig:

Code Snippet

1. using Autodesk.AutoCAD.ApplicationServices;
2. using Autodesk.AutoCAD.DatabaseServices;
3. using Autodesk.AutoCAD.EditorInput;
4. using Autodesk.AutoCAD.Geometry;
5.  
6. namespace NormJigs
7. {
8.     public class GuidedMovingJig : DrawJig
9.     {
10.         private Entity _entity=null;
11.         private Curve _curve=null;
12.         private Entity _offsetEntity = null;
13.         private Document _dwg;
14.         private Editor _ed;
15.         private Transaction _tran = null;
16.  
17.         private Point3d _originalPoint;
18.         private Point3d _previousPoint;
19.         private Point3d _currentPoint;
20.         private Point3d _finalPoint;
21.  
22.         private bool _dragCancelled = false;
23.  
24.         public GuidedMovingJig()
25.         {
26.             _dwg = Application.DocumentManager.MdiActiveDocument;
27.             _ed = _dwg.Editor;
28.         }
29.  
30.         public void DoDrag()
31.         {
32.             _dragCancelled = false;
33.  
34.             using (_tran =
35.                 _dwg.Database.TransactionManager.StartTransaction())
36.             {
37.                 if (GetEntities())
38.                 {
39.                     _entity.UpgradeOpen();
40.  
41.                     try
42.                     {
43.                         _entity.Highlight();
44.  
45.                         //Generate a clone entity as moving target
46.                         using (_offsetEntity = _entity.Clone() as Entity)
47.                         {
48.                             _offsetEntity.SetDatabaseDefaults();
49.  
50.                             //Place the moving target on guiding curve
51.                             Vector3d displacement =
52.                                 _originalPoint.GetVectorTo(_currentPoint);
53.                             _offsetEntity.TransformBy(
54.                                 Matrix3d.Displacement(displacement));
55.  
56.                             //Start drag
57.                             _ed.Drag(this);
58.                         }
59.  
60.                         //Move the entity to picked location after dragging
61.                         if (!_dragCancelled)
62.                         {
63.                             if (_finalPoint != _originalPoint)
64.                             {
65.                                 MoveEntity();
66.                             }
67.                         }
68.                     }
69.                     finally
70.                     {
71.                         //Make sure the entity is unhighlighted
72.                         _entity.Unhighlight();
73.                     }
74.                 }
75.  
76.                 _tran.Commit();
77.             }
78.         }
79.  
80.         protected override SamplerStatus Sampler(JigPrompts prompts)
81.         {
82.             JigPromptPointOptions jigOpt = new JigPromptPointOptions();
83.             jigOpt.UserInputControls =
84.                 UserInputControls.Accept3dCoordinates |
85.                 UserInputControls.NoZeroResponseAccepted |
86.                 UserInputControls.NoNegativeResponseAccepted;
87.  
88.             jigOpt.Message =
89.                 "\nMove to (pick a point or press Esc to cancel): ";
90.  
91.             PromptPointResult movePt = prompts.AcquirePoint(jigOpt);
92.  
93.             if (movePt.Status == PromptStatus.Cancel)
94.             {
95.                 _dragCancelled = true;
96.                 return SamplerStatus.Cancel;
97.             }
98.             else
99.             {
100.                 if (_previousPoint == movePt.Value)
101.                     return SamplerStatus.NoChange;
102.  
103.                 _currentPoint =
104.                     _curve.GetClosestPointTo(movePt.Value, false);
105.  
106.                 //Move the entity along the guiding curve
107.                 Vector3d displacement =
108.                     _previousPoint.GetVectorTo(_currentPoint);
109.                 _offsetEntity.TransformBy(
110.                     Matrix3d.Displacement(displacement));
111.  
112.                 _previousPoint = _currentPoint;
113.                 _finalPoint = _currentPoint;
114.  
115.                 return SamplerStatus.OK;
116.             }
117.         }
118.  
119.         protected override bool WorldDraw(
120.             Autodesk.AutoCAD.GraphicsInterface.WorldDraw draw)
121.         {
122.             draw.Geometry.Draw(_offsetEntity);
123.             return true;
124.         }
125.  
126.         #region private methods
127.  
128.         private bool GetEntities()
129.         {
130.             //Pick entity to be moved
131.             PromptEntityOptions entOpt =
132.                 new PromptEntityOptions("\nPick a moving entity: ");
133.             entOpt.SetRejectMessage(
134.                 "Invalid pick: must be AutoCAD entity.");
135.             entOpt.AddAllowedClass(typeof(Entity), false);
136.             PromptEntityResult entRes = _ed.GetEntity(entOpt);
137.             if (entRes.Status == PromptStatus.OK)
138.             {
139.                 _entity = (Entity)_tran.GetObject(
140.                     entRes.ObjectId, OpenMode.ForRead);
141.  
142.                 //Use picked point as default moving base point
143.                 Point3d pickedPt = entRes.PickedPoint;
144.  
145.                 PromptPointOptions ptOpt = new PromptPointOptions(
146.                     "\nPick moving entity's base point: <" +
147.                     pickedPt.X.ToString() + "," +
148.                     pickedPt.Y.ToString() + ">:");
149.                 ptOpt.AllowNone = true;
150.  
151.                 PromptPointResult ptRes = _ed.GetPoint(ptOpt);
152.                 if (ptRes.Status == PromptStatus.OK)
153.                 {
154.                     pickedPt = ptRes.Value;
155.                 }
156.                 else if (ptRes.Status == PromptStatus.None)
157.                 {
158.                     //Do nothing
159.                 }
160.                 else
161.                 {
162.                     return false;
163.                 }
164.  
165.                 _originalPoint = pickedPt;
166.                 
167.             }
168.             else
169.             {
170.                 return false;
171.             }
172.  
173.             //Pick guiding curve
174.             PromptEntityOptions curOpt = new PromptEntityOptions(
175.                 "\nPick a line/polyline/arc/circle as moving path: ");
176.             curOpt.SetRejectMessage(
177.                 "Invalid pick: must be a line, polyline, arc or circle.");
178.             curOpt.AddAllowedClass(typeof(Curve), false);
179.             PromptEntityResult curRes = _ed.GetEntity(curOpt);
180.             if (curRes.Status == PromptStatus.OK)
181.             {
182.                 _curve = (Curve)_tran.GetObject(
183.                     curRes.ObjectId, OpenMode.ForRead);
184.             }
185.             else
186.             {
187.                 return false;
188.             }
189.  
190.             _currentPoint =
191.                 _curve.GetClosestPointTo(_originalPoint, false);
192.             _previousPoint = _currentPoint;
193.             _finalPoint = _currentPoint;
194.  
195.             return true;
196.         }
197.  
198.         private void MoveEntity()
199.         {
200.             Vector3d displacement =
201.                 _originalPoint.GetVectorTo(_finalPoint);
202.             _entity.TransformBy(
203.                 Matrix3d.Displacement(displacement));
204.         }
205.  
206.         #endregion
207.     }
208. }

Since the code wraps all user input actions (picking moving entity and its moving base point, picking moving path), it is really simple to use GuidedMovingJig class. Here the command method to use it:

Code Snippet

1. using Autodesk.AutoCAD.ApplicationServices;
2. using Autodesk.AutoCAD.Runtime;
3. using Autodesk.AutoCAD.EditorInput;
4.  
5. [assembly: CommandClass(typeof(NormJigs.MyCommands))]
6.  
7. namespace NormJigs
8. {
9.     class MyCommands
10.     {
11.         [CommandMethod("MyMove")]
12.         public void UseMovingJig()
13.         {
14.             Document doc = Autodesk.AutoCAD.ApplicationServices.
15.                 Application.DocumentManager.MdiActiveDocument;
16.             Editor ed = doc.Editor;
17.  
18.             try
19.             {
20.                 GuidedMovingJig jig = new GuidedMovingJig();
21.                 jig.DoDrag();
22.             }
23.             catch(System.Exception ex)
24.             {
25.                 ed.WriteMessage("\nError: {0}\n", ex.Message);
26.             }
27.         }
28.     }
29. }

This video clip shows the GuidedMovingJig class in action.

Update on 20115-03-25

Recently, I saw a question in the discussion forum, asking how to do the same thing with a bit variation: the moving track is an arc (or circle, for that matter), and moving entity being dragged is also rotating when moving along the arc/circle, similar to how the moon moves around the earth. So, I thought I can fairly easy to update the code to make this Jig do that.

Here is the updated code.

using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.DatabaseServices;
using Autodesk.AutoCAD.EditorInput;
using Autodesk.AutoCAD.Geometry;
 
namespace NormJigs
{
    public class GuidedMovingJig : DrawJig
    {
        private Entity _entity = null;
        private Curve _curve = null;
        private Entity _offsetEntity = null;
        private Document _dwg;
        private Editor _ed;
        private Transaction _tran = null;
 
        private Point3d _originalPoint;
        private Point3d _previousPoint;
        private Point3d _currentPoint;
        private double _currentAngle = 0;
        private Point3d _finalPoint;
 
        private bool _doRotation = false;
 
        private bool _dragCancelled = false;
 
        public GuidedMovingJig()
        {
            _dwg = Application.DocumentManager.MdiActiveDocument;
            _ed = _dwg.Editor;
        }
 
        public void DoDrag(bool rotateAlonhgArc = false)
        {
            _dragCancelled = false;
            
            using (_tran =
                _dwg.Database.TransactionManager.StartTransaction())
            {
                if (GetEntities())
                {
                    if ((_curve is Circle || _curve is Arc) && rotateAlonhgArc)
                    {
                        _doRotation=true;
                    }
 
                    _entity.UpgradeOpen();
 
                    try
                    {
                        _entity.Highlight();
 
                        //Generate a clone entity as moving target
                        using (_offsetEntity = _entity.Clone() as Entity)
                        {
                            _offsetEntity.SetDatabaseDefaults();
 
                            //Place the moving target on guiding curve
                            Vector3d displacement =
                                _originalPoint.GetVectorTo(_currentPoint);
                            _offsetEntity.TransformBy(
                                Matrix3d.Displacement(displacement));
 
                            //Start drag
                            _ed.Drag(this);
                        }
 
                        //Move the entity to picked location after dragging
                        if (!_dragCancelled)
                        {
                            if (_finalPoint != _originalPoint)
                            {
                                MoveEntity();
                            }
                        }
                    }
                    finally
                    {
                        //Make sure the entity is unhighlighted
                        _entity.Unhighlight();
                    }
                }
 
                _tran.Commit();
            }
        }
 
        protected override SamplerStatus Sampler(JigPrompts prompts)
        {
            JigPromptPointOptions jigOpt = new JigPromptPointOptions();
            jigOpt.UserInputControls =
                UserInputControls.Accept3dCoordinates |
                UserInputControls.NoZeroResponseAccepted |
                UserInputControls.NoNegativeResponseAccepted;
 
            jigOpt.Message =
                "\nMove to (pick a point or press Esc to cancel): ";
 
            PromptPointResult movePt = prompts.AcquirePoint(jigOpt);
 
            if (movePt.Status == PromptStatus.Cancel)
            {
                _dragCancelled = true;
                return SamplerStatus.Cancel;
            }
            else
            {
                if (_previousPoint == movePt.Value)
                    return SamplerStatus.NoChange;
 
                _currentPoint =
                    _curve.GetClosestPointTo(movePt.Value, false);
 
                //Move the entity along the guiding curve
                Vector3d displacement =
                    _previousPoint.GetVectorTo(_currentPoint);
                _offsetEntity.TransformBy(
                    Matrix3d.Displacement(displacement));
 
                //Rotate the entity, if necessary
                if (_doRotation)
                {
                    //Rotate back to original angle
                    _offsetEntity.TransformBy(
                       Matrix3d.Rotation(0.0 - _currentAngle, Vector3d.ZAxis, _currentPoint));
 
                    //Calculate rotation angle
                    double angle = GetRotationAngle();
 
                    _offsetEntity.TransformBy(
                        Matrix3d.Rotation(angle, Vector3d.ZAxis, _currentPoint));
                    _currentAngle = angle;
                }
 
                _previousPoint = _currentPoint;
                _finalPoint = _currentPoint;
 
                return SamplerStatus.OK;
            }
        }
 
        protected override bool WorldDraw(
            Autodesk.AutoCAD.GraphicsInterface.WorldDraw draw)
        {
            draw.Geometry.Draw(_offsetEntity);
            return true;
        }
 
        #region private methods
 
        private bool GetEntities()
        {
            //Pick entity to be moved
            PromptEntityOptions entOpt =
                new PromptEntityOptions("\nPick an entity to move: ");
            entOpt.SetRejectMessage(
                "Invalid pick: must be AutoCAD entity.");
            entOpt.AddAllowedClass(typeof(Entity), false);
            PromptEntityResult entRes = _ed.GetEntity(entOpt);
            if (entRes.Status == PromptStatus.OK)
            {
                _entity = (Entity)_tran.GetObject(
                    entRes.ObjectId, OpenMode.ForRead);
 
                if (_entity is BlockReference)
                {
                    _originalPoint = ((BlockReference)_entity).Position;
                }
                else
                {
                    //Use picked point as default moving base point
                    Point3d pickedPt = entRes.PickedPoint;
 
                    PromptPointOptions ptOpt = new PromptPointOptions(
                        "\nPick moving entity's base point: <" +
                        pickedPt.X.ToString() + "," +
                        pickedPt.Y.ToString() + ">:");
                    ptOpt.AllowNone = true;
 
                    PromptPointResult ptRes = _ed.GetPoint(ptOpt);
                    if (ptRes.Status == PromptStatus.OK)
                    {
                        pickedPt = ptRes.Value;
                    }
                    else if (ptRes.Status == PromptStatus.None)
                    {
                        //Do nothing
                    }
                    else
                    {
                        return false;
                    }
 
                    _originalPoint = pickedPt;
                }
            }
            else
            {
                return false;
            }
 
            //Pick guiding curve
            PromptEntityOptions curOpt = new PromptEntityOptions(
                "\nPick a line/polyline/arc/circle as moving path: ");
            curOpt.SetRejectMessage(
                "Invalid pick: must be a line, polyline, arc or circle.");
            curOpt.AddAllowedClass(typeof(Curve), false);
            PromptEntityResult curRes = _ed.GetEntity(curOpt);
            if (curRes.Status == PromptStatus.OK)
            {
                _curve = (Curve)_tran.GetObject(
                    curRes.ObjectId, OpenMode.ForRead);
            }
            else
            {
                return false;
            }
 
            _currentPoint =
                _curve.GetClosestPointTo(_originalPoint, false);
            _previousPoint = _currentPoint;
            _finalPoint = _currentPoint;
 
            return true;
        }
 
        private double GetRotationAngle()
        {
            double ang = 0.0;
 
            //Find circle/arc centre
            Point3d center = (_curve is Arc) ? ((Arc)_curve).Center : ((Circle)_curve).Center;
 
            //Calculate angle. Because of my laziness, I took this shortcut
            using (var line = new Line(center, _currentPoint))
            {
                ang = line.Angle;
            }
 
            return ang;
        }
 
        private void MoveEntity()
        {
            Vector3d displacement =
                _originalPoint.GetVectorTo(_finalPoint);
            _entity.TransformBy(
                Matrix3d.Displacement(displacement));
 
            if (_doRotation)
            {
                double angle = GetRotationAngle();
 
                _entity.TransformBy(
                    Matrix3d.Rotation(angle, Vector3d.ZAxis, _finalPoint));
            }
        }
 
        #endregion
    }
}

In the updated code, a class level member _currentAngle is added and an optional argument in the public method DoDrag() is added to indicate whether the dragged entity rotates or not when the track is an arc or a circle. Then the code in the overridden Sampler() is updated accordingly, so that the dragged entity rotates as needed.

Here is the updated command class:

using Autodesk.AutoCAD.ApplicationServices;
using Autodesk.AutoCAD.Runtime;
using Autodesk.AutoCAD.EditorInput;
 
[assembly: CommandClass(typeof(NormJigs.MyCommands))]
 
namespace NormJigs
{
    class MyCommands
    {
        [CommandMethod("MyMove")]
        public void UseMovingJig()
        {
            Document doc = Autodesk.AutoCAD.ApplicationServices.
                Application.DocumentManager.MdiActiveDocument;
            Editor ed = doc.Editor;
 
            try
            {
                GuidedMovingJig jig = new GuidedMovingJig();
                jig.DoDrag(true);
            }
            catch (System.Exception ex)
            {
                ed.WriteMessage("\nError: {0}\n", ex.Message);
            }
        }
    }
}

See this video clip for the action of the updated code.