★中望CAD 二次开发JIG实体如何动态输入长度绘制直线？

问题描述： 

实现类似动态绘制直线时，在【动态绘制过程】输入长度，就可以绘制直线，该如何实现呢？
测试了一下Drawjig类，发现【prompts.AcquireDistance】支持输入长度，但是只返回长度，没有角度无法确定下一点。然后【prompts.AcquirePoint】直接返回下一点，但不支持用户输入长度。

步骤指引：

1. 可以使用AcquirePoint + 接管用户输入。

2. 缓存基点（起点）

3. 缓存最近一次鼠标方向向量

4. 如果输入是字符串 / 数字 → 自己算点

   class LineLengthJig : DrawJig
   {
       private Point3d _basePt;
       private Point3d _curPt;
       private Vector3d _dir = Vector3d.XAxis;
   
       public LineLengthJig(Point3d basePt)
       {
           _basePt = basePt;
           _curPt = basePt;
       }
   
       protected override SamplerStatus Sampler(JigPrompts prompts)
       {
           JigPromptPointOptions opt =
               new JigPromptPointOptions("\n指定下一点或输入长度:");
   
           opt.BasePoint = _basePt;
           opt.UseBasePoint = true;
   
           opt.UserInputControls =
               UserInputControls.Accept3dCoordinates |
               UserInputControls.AcceptOtherInputString;
   
           PromptPointResult res = prompts.AcquirePoint(opt);
   
           // 鼠标输入
           if (res.Status == PromptStatus.OK)
           {
               if (_curPt == res.Value)
                   return SamplerStatus.NoChange;
   
               _curPt = res.Value;
               _dir = _basePt.GetVectorTo(_curPt);
               return SamplerStatus.OK;
           }
   
           // 键盘输入（长度）
           if (res.Status == PromptStatus.Other)
           {
               if (double.TryParse(res.StringResult, out double len))
               {
                   if (_dir.Length < Tolerance.Global.EqualPoint)
                       _dir = Vector3d.XAxis; // 默认方向
   
                   _curPt = _basePt + _dir.GetNormal() * len;
                   return SamplerStatus.OK;
               }
           }
   
           return SamplerStatus.Cancel;
       }
   
       protected override bool WorldDraw(WorldDraw draw)
       {
           draw.Geometry.WorldLine(_basePt, _curPt);
           return true;
       }
   
       public Point3d EndPoint => _curPt;
   }
   
   [CommandMethod("JIGLINE")]
   public void JigLine()
   {
       Editor ed = Application.DocumentManager.MdiActiveDocument.Editor;
   
       PromptPointResult ppr =
           ed.GetPoint("\n指定起点:");
   
       if (ppr.Status != PromptStatus.OK)
           return;
   
       LineLengthJig jig = new LineLengthJig(ppr.Value);
   
       if (ed.Drag(jig).Status == PromptStatus.OK)
       {
           using (Transaction tr =
               ed.Document.Database.TransactionManager.StartTransaction())
           {
               Line ln = new Line(ppr.Value, jig.EndPoint);
               BlockTableRecord btr =
                   (BlockTableRecord)tr.GetObject(
                       SymbolUtilityServices.GetBlockModelSpaceId(
                           ed.Document.Database),
                       OpenMode.ForWrite);
   
               btr.AppendEntity(ln);
               tr.AddNewlyCreatedDBObject(ln, true);
               tr.Commit();
           }
       }
   }

★中望CAD 二次开发JIG实体如何动态输入长度绘制直线？：https://confluence.zwcad.com/pages/viewpage.action?pageId=308806170