In the last post we used an API introduced in AutoCAD 2011 to trace boundaries defined by geometry in a drawing. In this post we're going to use these boundaries to define the limits of solid hatch objects which we will – using another new capability in AutoCAD 2011 - make transparent.
Here's the updated C# code to define our TBH command with new/changed lines in red (you can also get the source file without line numbers here):
1 using Autodesk.AutoCAD.ApplicationServices;
2 using Autodesk.AutoCAD.EditorInput;
3 using Autodesk.AutoCAD.DatabaseServices;
4 using Autodesk.AutoCAD.Runtime;
5 using Autodesk.AutoCAD.Colors;
6
7 namespace TraceBoundaryWithHatch
8 {
9 public class Commands
10 {
11 static int _index = 1;
12
13 [CommandMethod("TBH")]
14 public void TraceBoundaryAndHatch()
15 {
16 Document doc =
17 Application.DocumentManager.MdiActiveDocument;
18 Database db = doc.Database;
19 Editor ed = doc.Editor;
20
21 // Select a seed point for our boundary
22
23 PromptPointResult ppr =
24 ed.GetPoint("\nSelect internal point: ");
25
26 if (ppr.Status != PromptStatus.OK)
27 return;
28
29 // Get the objects making up our boundary
30
31 DBObjectCollection objs =
32 ed.TraceBoundary(ppr.Value, false);
33
34 if (objs.Count > 0)
35 {
36 Transaction tr =
37 doc.TransactionManager.StartTransaction();
38 using (tr)
39 {
40 // We'll add the objects to the model space
41
42 BlockTable bt =
43 (BlockTable)tr.GetObject(
44 doc.Database.BlockTableId,
45 OpenMode.ForRead
46 );
47
48 BlockTableRecord btr =
49 (BlockTableRecord)tr.GetObject(
50 bt[BlockTableRecord.ModelSpace],
51 OpenMode.ForWrite
52 );
53
54 // Add our boundary objects to the drawing and
55 // collect their ObjectIds for later use
56
57 ObjectIdCollection ids = new ObjectIdCollection();
58 foreach (DBObject obj in objs)
59 {
60 Entity ent = obj as Entity;
61 if (ent != null)
62 {
63 // Set our boundary objects to be of
64 // our auto-incremented colour index
65
66 ent.ColorIndex = _index;
67
68 // Set our transparency to 50% (=127)
69 // Alpha value is Truncate(255 * (100-n)/100)
70
71 ent.Transparency = new Transparency(127);
72
73 // Add each boundary object to the modelspace
74 // and add its ID to a collection
75
76 ids.Add(btr.AppendEntity(ent));
77 tr.AddNewlyCreatedDBObject(ent, true);
78 }
79 }
80
81 // Create our hatch
82
83 Hatch hat = new Hatch();
84
85 // Solid fill of our auto-incremented colour index
86
87 hat.SetHatchPattern(
88 HatchPatternType.PreDefined,
89 "SOLID"
90 );
91 hat.ColorIndex = _index++;
92
93 // Set our transparency to 50% (=127)
94 // Alpha value is Truncate(255 * (100-n)/100)
95
96 hat.Transparency = new Transparency(127);
97
98 // Add the hatch to the modelspace & transaction
99
100 ObjectId hatId = btr.AppendEntity(hat);
101 tr.AddNewlyCreatedDBObject(hat, true);
102
103 // Add the hatch loops and complete the hatch
104
105 hat.Associative = true;
106 hat.AppendLoop(
107 HatchLoopTypes.Default,
108 ids
109 );
110
111 hat.EvaluateHatch(true);
112
113 // Commit the transaction
114
115 tr.Commit();
116 }
117 }
118 }
119 }
120 }
A few things to note about this implementation:
- We choose not to detect islands when using the results to create a hatch
- Hatches clearly support islands, but we would make separate calls to AppendLoop() to add them
- It should be possible to detect islands whether geometrically or by diffing the results of two calls to TraceBoundary(), one detecting islands, one not
- We've applied transparency both to the boundary objects and the hatch
- We no longer set the lineweight on the boundary objects
- The Alpha-based transparency value isn't as simple as using a straight percentage
- After doing some tests (setting the transparency as a percentage and running a simple command to print the Alpha value to the command-line), I found that the value stored actually seems to reflect "opacity" rather than transparency (i.e. it's an inverse relationship), so we subtract our percentage from 100 before applying it to the total of 255 (and truncating – not rounding – the result)
- It also appears you can't have transparency of higher than 90% (at least not according to my tests)
- In our case we're just using 50% transparency
Here's what happens when we run our TBH command on the boundaries we used to test the code in the last post.
Before…
After…
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