Creating My Own "Scale" Command

In certain situation when we develop our AutoCAD add-ins, using a custom command, instead of AutoCAD built-in command, might be preferred and allow our add-in to have more control to specific drafting procedures/steps.

Using DrawJig class we can quite easily to create our own commands that behave similar to, or the same way as, AutoCAD built-in commands, like Move, Copy, Scale, Stretch...

Here I show some code to create a custom "Scale" command that behaves very similar to AutoCAD built-in "Scale" command: user selects an entity, picks a base point, then moves/drags the mouse cursor until the mouse is clicked or a scale number is entered. During mouse dragging, a ghost image of the selected entity dynamically scales in or out, depending on the distance between the cursor's location and the base point.

Here is the class MyScaleJig:

Code Snippet

1. using System;
2. using Autodesk.AutoCAD.ApplicationServices;
3. using Autodesk.AutoCAD.DatabaseServices;
4. using Autodesk.AutoCAD.EditorInput;
5. using Autodesk.AutoCAD.Geometry;
6.  
7. namespace ScaleJig
8. {
9.     public class MyScaleJig : DrawJig
10.     {
11.         private Document _dwg;
12.         private Editor _ed;
13.         private Database _db;
14.  
15.         private ObjectId _entID;
16.  
17.         private Entity _entity=null;
18.         private int _colorIndex = 0;
19.         private Point3d _basePoint;
20.  
21.         private double _scale = 1.0;
22.         private bool _picked = false;
23.  
24.         public MyScaleJig(Document dwg):base()
25.         {
26.             _dwg = dwg;
27.             _ed = _dwg.Editor;
28.             _db = _dwg.Database;
29.         }
30.  
31.         public void ScaleEntity(ObjectId entID, int ghostLineColorIndex)
32.         {
33.             _entID = entID;
34.             _colorIndex = ghostLineColorIndex;
35.  
36.             //Highlight entity
37.             HighlightEntity(true);
38.  
39.             //Pick base point
40.             if (PickBasePoint())
41.             {
42.                 //Use a non-database residing
43.                 //entity for showing jig ghost line
44.                 using (_entity = GetEntityClone(_entID))
45.                 {
46.                     _ed.Drag(this);
47.                 }
48.  
49.                 //Unhighlight
50.                 HighlightEntity(false);
51.  
52.                 //Tramsform(scale) entity
53.                 //if user did not cancel the jig
54.                 if (_picked) ScaleEntity();
55.             }
56.         }
57.  
58.         #region override Jig methods
59.         
60.         protected override SamplerStatus Sampler(JigPrompts prompts)
61.         {
62.             JigPromptDistanceOptions opt = new JigPromptDistanceOptions(
63.                 "\nMove cursor to scale entity or enter scale:");
64.             opt.DefaultValue = _scale;
65.             opt.UseBasePoint = true;
66.             opt.BasePoint = _basePoint;
67.             opt.UserInputControls =
68.                 UserInputControls.Accept3dCoordinates |
69.                 UserInputControls.AcceptOtherInputString |
70.                 UserInputControls.NoNegativeResponseAccepted |
71.                 UserInputControls.NoZeroResponseAccepted |
72.                 UserInputControls.NullResponseAccepted;
73.             opt.Cursor = CursorType.RubberBand;
74.  
75.             PromptDoubleResult res = prompts.AcquireDistance(opt);
76.  
77.             SamplerStatus status;
78.  
79.             if (res.Status == PromptStatus.OK)
80.             {
81.                 double newScale = res.Value;
82.  
83.                 if (Math.Abs(_scale-newScale)<0.0001)
84.                 {
85.                     status = SamplerStatus.NoChange;
86.                 }
87.                 else
88.                 {
89.                     Matrix3d mt;
90.  
91.                     //Restore to previous scale
92.                     mt = Matrix3d.Scaling(1 / _scale, _basePoint);
93.                     _entity.TransformBy(mt);
94.  
95.                     //Transform to new scale
96.                     _scale = newScale;
97.                     mt = Matrix3d.Scaling(_scale, _basePoint);
98.                     _entity.TransformBy(mt);
99.  
100.                     status = SamplerStatus.OK;
101.                 }
102.  
103.                 _picked = true;
104.             }
105.             else
106.             {
107.                 _picked = false;
108.                 status = SamplerStatus.Cancel;
109.             }
110.  
111.             return status;
112.         }
113.  
114.         protected override bool WorldDraw(
115.             Autodesk.AutoCAD.GraphicsInterface.WorldDraw draw)
116.         {
117.             
118.             draw.Geometry.Draw(_entity);
119.             return true;
120.         }
121.  
122.         #endregion
123.  
124.         #region private methods
125.  
126.         private Entity GetEntityClone(ObjectId entID)
127.         {
128.             Entity ent = null;
129.             using (Transaction tran =
130.                 _db.TransactionManager.StartTransaction())
131.             {
132.                 Entity e = (Entity)tran.GetObject(entID, OpenMode.ForRead);
133.                 ent = e.Clone() as Entity;
134.                 ent.ColorIndex = _colorIndex;
135.  
136.                 tran.Commit();
137.             }
138.  
139.             return ent;
140.         }
141.  
142.         private void HighlightEntity(bool highlight)
143.         {
144.             using (Transaction tran =
145.                 _db.TransactionManager.StartTransaction())
146.             {
147.                 Entity ent = (Entity)tran.GetObject(
148.                     _entID, OpenMode.ForWrite);
149.                 SubentityId subEntId =
150.                     new SubentityId(SubentityType.Null, IntPtr.Zero);
151.                 ObjectId[] ids = new ObjectId[1];
152.                 ids[0] = ent.ObjectId;
153.                 FullSubentityPath path =
154.                     new FullSubentityPath(ids, subEntId);
155.  
156.                 if (highlight)
157.                     ent.Highlight(path, true);
158.                 else
159.                     ent.Unhighlight(path, true);
160.             }
161.         }
162.  
163.         private bool PickBasePoint()
164.         {
165.             PromptPointOptions opt = new PromptPointOptions(
166.                 "\nPick scale base point:");
167.             opt.AllowNone = false;
168.             PromptPointResult res = _ed.GetPoint(opt);
169.  
170.             if (res.Status == PromptStatus.OK)
171.             {
172.                 _basePoint = res.Value;
173.                 return true;
174.             }
175.             else
176.             {
177.                 return false;
178.             }
179.         }
180.  
181.         private void ScaleEntity()
182.         {
183.             using (Transaction tran =
184.                 _db.TransactionManager.StartTransaction())
185.             {
186.                 Entity e = (Entity)tran.GetObject(_entID, OpenMode.ForWrite);
187.  
188.                 Matrix3d mt = Matrix3d.Scaling(_scale, _basePoint);
189.                 e.TransformBy(mt);
190.  
191.                 tran.Commit();
192.             }
193.         }
194.  
195.         #endregion
196.     }
197. }

Here is a command class that uses MyScaleJig to scale selected entity:

Code Snippet

1. using Autodesk.AutoCAD.ApplicationServices;
2. using Autodesk.AutoCAD.DatabaseServices;
3. using Autodesk.AutoCAD.EditorInput;
4. using Autodesk.AutoCAD.Runtime;
5.  
6. [assembly: CommandClass(typeof(ScaleJig.MyCommands))]
7.  
8. namespace ScaleJig
9. {
10.     public class MyCommands
11.     {
12.         [CommandMethod("MyScale")]
13.         public static void RunMyScaleJig()
14.         {
15.             Document doc = Application.DocumentManager.MdiActiveDocument;
16.             Editor ed = doc.Editor;
17.  
18.             //Pick an entity
19.             ObjectId entID = GetEntity(ed);
20.             if (entID == ObjectId.Null)
21.             {
22.                 ed.WriteMessage("\n*Cancel*");
23.                 return;
24.             }
25.  
26.             //Use MyScaleJig to scale entity
27.             //With red jib ghost line
28.             MyScaleJig jig = new MyScaleJig(doc);
29.             jig.ScaleEntity(entID, 1);
30.         }
31.  
32.         private static ObjectId GetEntity(Editor ed)
33.         {
34.             PromptEntityOptions opt =
35.                 new PromptEntityOptions("\nPick an entity: ");
36.             PromptEntityResult res = ed.GetEntity(opt);
37.  
38.             if (res.Status == PromptStatus.OK)
39.             {
40.                 return res.ObjectId;
41.             }
42.             else
43.             {
44.                 return ObjectId.Null;
45.             }
46.         }
47.     }
48. }

The key part of the code lies in the 2 overridden methods Sampler() and WorldDraw() and it is quite simple and straightforward.

I uses a non-database residing, cloned entity for generating ghost image of the entity to be scaled. This way, the real entity to scaled is not changed if user cancels dragging, and only be changed when the dragging is ended with a distance (scale) is picked or entered.

As we can see, the whole purpose to use jig here is to get a scale input from user with very user-friendly visual hint help.

With some easy code modification, we can pass a collection/array of selected entities (ObjectIds, actually), and scale them together.

However, comparing to AutoCAD built-in Scale command, one thing is missing: there is no rubber-band line from the base point to the mouse cursor. That is because I have use JigPromptDistanceOptions to acquire user input as scale. In spite I set its UseBasePoint property to True and set its BasePoint property to a Point3d value, the rubber-band line still does not show. I guess this is by design: rubber-band line only shows with JigPromptPointOptions class.
I do not know how to overcome this problem with Jig class. Maybe I can implement another custom Scale command with TransientGraphics in conjunction with Editor.PointMonitor event handler later.

Update: Thanks to Maxence's comment, it turned out showing the rubber-band line is simple. I added one line code, showing in red. Thank you, Maxence.