AutoCAD C# 两不平行直线倒圆弧算法

参考的博客：https://www.cnblogs.com/JJBox/p/14300098.html

下面是计算示例

主要计算代码：

   var peo = new PromptEntityOptions("选择直线1")
   {
       AllowNone = false,
       AllowObjectOnLockedLayer = false
   };
   peo.SetRejectMessage("请选择直线Line");
   peo.AddAllowedClass(typeof(Line), false);
   var per1 = AcEnv.CurEd.GetEntity(peo);
   peo.Message = "选择直线2";
   var per2 = AcEnv.CurEd.GetEntity(peo);
   var r = AcEnv.CurEd.GetDouble("输入圆弧半径:\n").Value;
   if (per1.Status == PromptStatus.OK && per2.Status == PromptStatus.OK)
   {
       using (var tr = AcEnv.CurDb.TransactionManager.StartTransaction())
       {
           var l1 = (Line)tr.GetObject(per1.ObjectId, OpenMode.ForRead);
           var l2 = (Line)tr.GetObject(per2.ObjectId, OpenMode.ForRead);
           var pts = new Point3dCollection();
           l1.IntersectWith(l2, Intersect.ExtendBoth, l1.GetPlane(), pts, IntPtr.Zero, IntPtr.Zero);
           if (pts.Count == 0)
           {
               AcApp.Application.ShowAlertDialog("2直线无交点无法到圆角！");
               tr.Abort();
               return;
           }
           var p0 = pts[0];
           var p02d = p0.Convert2d(l1.GetPlane());
           var voa = p0.GetVectorTo(l1.EndPoint.GetMidPoint(l1.StartPoint));
           var vob = p0.GetVectorTo(l2.EndPoint.GetMidPoint(l2.StartPoint));
           var angle = voa.GetAngleTo(vob) * 0.5;
           var doc = r / Math.Sin(angle);
           var pa = p0.Add(voa.GetNormal() * (double)(r / Math.Tan(angle)));
           var pb = p0.Add(vob.GetNormal() * (double)(r / Math.Tan(angle)));
           var isCw = Tools.CrossAclockwise(p02d, pa.Convert2d(l1.GetPlane()), pb.Convert2d(l1.GetPlane()));
           var pc = pa.Add((isCw ? voa : voa.Negate()).GetPerpendicularVector().GetNormal() * r);
           var startAngle = pc.GetVectorTo(pb).Convert2d(l1.GetPlane()).GetAngle2XAxis();
           var endAngle = pc.GetVectorTo(pa).Convert2d(l1.GetPlane()).GetAngle2XAxis();
           Arc a = new Arc(pc, Vector3d.ZAxis, r, isCw ? startAngle : endAngle, isCw ? endAngle : startAngle);
           //AcEnv.CurDb.AppendEntities(new DBPoint(p0), new DBPoint(pa), new DBPoint(pb), new DBPoint(pc));
           AcEnv.CurDb.AppendEntities(a);
           tr.Commit();
       }
   }

用到的拓展函数

    public static Point3d GetMidPoint(this Point3d p1, Point3d p2)
    {
        return new Point3d((p1.X + p2.X) * 0.5, (p1.Y + p2.Y) * 0.5, (p1.Z + p2.Z) * 0.5);
    }
    /// <summary>
    /// 叉积,二维叉乘计算
    /// </summary>
    /// <param name="a">传参是向量,表示原点是0,0</param>
    /// <param name="b">传参是向量,表示原点是0,0</param>
    /// <returns>其模为a与b构成的平行四边形面积</returns>
    public static double Cross(Vector2d a, Vector2d b)
    {
        return a.X * b.Y - a.Y * b.X;
    }

    /// <summary>
    /// 叉积,二维叉乘计算 
    /// </summary>
    /// <param name="o">原点</param>
    /// <param name="a">oa向量</param>
    /// <param name="b">ob向量,此为判断点</param>
    /// <returns>返回值有正负,表示绕原点四象限的位置变换,也就是有向面积</returns>
    public static double Cross(Point2d o, Point2d a, Point2d b)
    {
        return Cross(o.GetVectorTo(a), o.GetVectorTo(b));
    }

    /// <summary>
    /// 叉积,逆时针方向为真
    /// </summary>
    /// <param name="o">直线点1</param>
    /// <param name="a">直线点2</param>
    /// <param name="b">判断点</param>
    /// <returns>b点在oa的逆时针<see cref="true"/></returns>
    public static bool CrossAclockwise(Point2d o, Point2d a, Point2d b)
    {
        return Cross(o, a, b) > -1e-6;//浮点数容差考虑
    }

    /// <summary>
    /// X轴到向量的弧度,cad的获取的弧度是1PI,所以转换为2PI(上小,下大)
    /// </summary>
    /// <param name="ve">向量</param>
    /// <returns>弧度</returns>
    public static double GetAngle2XAxis(this Vector2d ve)
    {
        double alz = Vector2d.XAxis.GetAngleTo(ve);//观察方向不要设置 
        alz = ve.Y > 0 ? alz : Math.PI * 2 - alz; //逆时针为正,如果-负值控制正反
        alz = Math.Abs(Math.PI * 2 - alz) < 1e-10 ? 0 : alz;
        return alz;
    }
  public static ObjectIdCollection AppendEntities(this Database acdb, params Entity[] ents)
  {
      ObjectIdCollection oids = [];
      using (var tr = acdb.TransactionManager.StartTransaction())
      {
          var btr = (BlockTableRecord)acdb.CurrentSpaceId.GetObject(OpenMode.ForWrite);
          foreach (var item in ents)
          {
              if (!item.IsNewObject) continue;
              oids.Add(btr.AppendEntity(item));
              tr.AddNewlyCreatedDBObject(item, true);
          }
          tr.Commit();
      }
      return oids;
  }
}