CAD(C#)——"小知识点"

①: 隐藏实体

     在CAD的开发中，有时候我们需要根据用户的需求隐藏和显示一些实体，对于实体本身的属性Visible当然可以实现隐藏、显示实体，不过，除此之外，我们还可以将一个层上的实体同时隐藏起来，这就要使用LayerTableRecord中的IsOff属性，并且隐藏的实体ObjectId可以出现在SelectAll()的集合中.当然，他们之间还是有区别的，当你用Ctrl+A，选中当前活动文档的全部实体是，你就会发现原来他们之间区别。

     简单的测试程序：

 1  #region 测试图层的IsOff和实体的Visible是否一致
 2         [CommandMethod("TestLayer")]
 3         public void TestLayerVis()
 4         {
 5             //选择一点创建实体
 6             PromptPointOptions opt = new PromptPointOptions("选择起始点:");
 7             PromptPointResult res = ed.GetPoint(opt);
 8             if (PromptStatus.OK == res.Status)
 9             {
10                 Point3d sPt = res.Value;
11                 using (Transaction trans = db.TransactionManager.StartTransaction())
12                 {
13                     BlockTable bt = (BlockTable)trans.GetObject(db.BlockTableId, OpenMode.ForRead);
14                     BlockTableRecord btr = (BlockTableRecord)trans.GetObject(db.CurrentSpaceId, OpenMode.ForWrite);
15                     //直线，其所在层为默认的层
16                     Line line = new Line();
17                     line.StartPoint = sPt;
18                     line.EndPoint = new Point3d(sPt.X + 100, sPt.Y + 50, 0);
19                     //圆，指定层
20                     Circle c = new Circle(sPt, new Vector3d(0, 0, 1), 30);
21                     c.LayerId = CreateLayer("TestLayer");
22                     line.Visible = false; //不显示实体
23                     btr.AppendEntity(line);
24                     btr.AppendEntity(c);
25                     trans.AddNewlyCreatedDBObject(line, true);
26                     trans.AddNewlyCreatedDBObject(c, true);
27 
28                     LayerTable lt = (LayerTable)trans.GetObject(db.LayerTableId, OpenMode.ForRead);
29                     LayerTableRecord ltr = (LayerTableRecord)trans.GetObject(CreateLayer("TestLayer"), OpenMode.ForWrite);
30                     ltr.IsOff = true; //关闭图层，隐藏图层上的实体
31 
32                     trans.Commit();
33                 }
34             }
35         }
36 
37         //创建一个图层
38         private ObjectId CreateLayer(string layerName)
39         {
40             ObjectId objId = ObjectId.Null;
41             using (Transaction trans = db.TransactionManager.StartTransaction())
42             {
43                 LayerTable lt = (LayerTable)trans.GetObject(db.LayerTableId, OpenMode.ForWrite);
44                 if (lt.Has(layerName))
45                 {
46                     objId = lt[layerName];
47                 }
48                 else
49                 {
50                     LayerTableRecord ltr = new LayerTableRecord();
51                     ltr.Name = layerName;
52                     objId = lt.Add(ltr);
53                     trans.AddNewlyCreatedDBObject(ltr, true);
54                     trans.Commit();
55                 }
56             }
57 
58             return objId;
59         }
60        #endregion 

②:修改线宽

     有的时候我们为了打印出来的图片更加的清楚，可能会设计到修改实体的线宽,对于多段线，我们很容易想到使用ConstantWidth，这样就可以修改其线宽了，其实，对于圆或是直线也一样，不过我们在修改他们的线宽之前要保证系统变量的lwdisplay的值为1(开),这时我们再设置LineWeight,就可以改变他们的线宽了。

     简单的测试程序：

 1  #region 测试直线、圆的LineWeight和PolyLine的ConstantWidth之间的区别
 2         [CommandMethod("TestLW")]
 3         public void TestLW()
 4         {
 5             PromptPointOptions opt = new PromptPointOptions("选择起点:");
 6             PromptPointResult res = ed.GetPoint(opt);
 7             if (PromptStatus.OK == res.Status)
 8             {
 9                 Point3d sPt = res.Value;
10                 ObjectId plId = ObjectId.Null;
11                 ObjectId circleId = ObjectId.Null;
12                 using (Transaction trans = db.TransactionManager.StartTransaction())
13                 {
14                     BlockTable bt = (BlockTable)trans.GetObject(db.BlockTableId, OpenMode.ForRead);
15                     BlockTableRecord btr = (BlockTableRecord)trans.GetObject(db.CurrentSpaceId, OpenMode.ForWrite);
16 
17                     //创建一个多段线
18                     Polyline pl = new Polyline();
19                     pl.AddVertexAt(0, sPt.Convert2d(new Plane()), 0, 0, 0);
20                     pl.AddVertexAt(1, new Point3d(sPt.X + 100, sPt.Y + 50, 0).Convert2d(new Plane()), 0, 0, 0);
21                     pl.AddVertexAt(2, new Point3d(sPt.X + 150, sPt.Y - 150, 0).Convert2d(new Plane()), 0, 0, 0);
22 
23                     //创建一个圆
24                     Circle c = new Circle(sPt, new Vector3d(0, 0, 1), 40);
25 
26                     plId = btr.AppendEntity(pl);
27                     circleId = btr.AppendEntity(c);
28                     trans.AddNewlyCreatedDBObject(pl, true);
29                     trans.AddNewlyCreatedDBObject(c, true);
30                     //修改线宽
31                     pl.ConstantWidth = 0.15;
32                     c.LineWeight = LineWeight.LineWeight035;//绝对线宽
33 
34                     trans.Commit();
35                 }
36             }
37         }
38         #endregion

③:多段线凸起

      这个功能一般用在两条多段线相交时，区分多段线的走向而特意使相交的多段线在交点出凸起一个"小弧",在这个应用中，我们会发现PolyLine中的AddVertexAt的奇妙之处(插入点的序号可以小于PLine的节点数目，PLine的原有节点的序号会因为有新插入点而自增)。    

      简单的测试程序：

 1  [CommandMethod("TestPolyLine")]
 2         public void TestPolyLine()
 3         {
 4             PromptPointOptions opt = new PromptPointOptions("选择起点:");
 5             PromptPointResult res = ed.GetPoint(opt);
 6             if (PromptStatus.OK == res.Status)
 7             {
 8                 Point3d sPt = res.Value;
 9                 ObjectId plId = ObjectId.Null;
10                 ObjectId circleId = ObjectId.Null;
11                 Polyline pl = new Polyline();
12                 using (Transaction trans = db.TransactionManager.StartTransaction())
13                 {
14                     BlockTable bt = (BlockTable)trans.GetObject(db.BlockTableId, OpenMode.ForRead);
15                     BlockTableRecord btr = (BlockTableRecord)trans.GetObject(db.CurrentSpaceId, OpenMode.ForWrite);
16 
17                     //创建一个多段线
18                     pl.AddVertexAt(0, sPt.Convert2d(new Plane()), 0, 0, 0);
19                     pl.AddVertexAt(1, new Point3d(sPt.X + 200, sPt.Y + 150, 0).Convert2d(new Plane()), 0, 0, 0);
20                     pl.AddVertexAt(2, new Point3d(sPt.X + 400, sPt.Y + 80, 0).Convert2d(new Plane()), 0, 0, 0);
21 
22                     btr.AppendEntity(pl);
23                     trans.AddNewlyCreatedDBObject(pl, true);
24                     ////加一个小弧
25                     Point3d pt1 = pl.GetPointAtDist(80);
26                     Point3d pt2 = pl.GetPointAtDist(100);
27                     pl.AddVertexAt(1, pt1.Convert2d(new Plane()), 0, 0, 0);
28                     pl.AddVertexAt(2, pt2.Convert2d(new Plane()), 0, 0, 0);
29                     pl.SetBulgeAt(1, 0.78);
30                     
31                     trans.Commit();
32                 }
33                 
34             }
35         }