在08科创项目，绘图助手工具箱中的第二、三个命令RTLine、STLine就是使用了曲线打断的函数，为实现这个命令我查阅了多个网页，找出了几个重要的函数，分别是打断曲线的getSplitCurves、求两曲线交点的intersectwith。感谢ObjectARX编程站，让我找到很多ObjectARX方面我需要的东西，以下就是我转载的文章：

创建自己的曲线打断命令

 原文地址：http://www.objectarx.net/bbs/viewthread.php?tid=1655&extra=page%3D1%26amp%3Bfilter%3Ddigest

 void drawEntity(AcDbEntity* pEntity);
 bool breakCurve(AcDbCurve* curve, AcGePoint3d pt);
 bool breakCurve(AcDbCurve* curve, AcGePoint3d p1, AcGePoint3d p2);


 static void Mybreak2008_Mybreak(void)
 {
     // Add your code for command Mybreak2008._Mybreak here
     ads_point pt1,pt2;
     ads_name entName;
     Acad::ErrorStatus es;
     int ret;
     ACHAR kWord[100];


     if (acedEntSel(_T("\n选择所要打断的曲线："), entName, pt1) !=RTNORM)
     {
         return;
     }
     AcDbObjectId entId;
     AcDbCurve *pCurve=NULL;
     AcDbEntity *pEnt = NULL;
     es = acdbGetObjectId(entId, entName);
     if (es != Acad::eOk)
     {
        return;
     }
     acdbOpenObject(pEnt, entId, AcDb::kForWrite);
     if (pEnt->isKindOf(AcDbCurve::desc()))
     {
        pCurve = AcDbCurve::cast(pEnt);
        if (pCurve != NULL)
        {
           acedInitGet (NULL, _T("F"));
           ret=acedGetPoint(NULL,_T("\n指定第二个打断点或[第一点(F)]:"),pt2);
           switch (ret)
           {
               case RTKWORD:
                   ret=acedGetInput(kWord);
                   if ( ret!= RTNORM )
                       break ;
                   acedInitGet(RSG_NONULL, _T(""));
                   ret=acedGetPoint(NULL,_T("\n指定第一个打断点:"),pt1);
                   if (ret!=RTNORM)
                       break;
                   acedInitGet(RSG_NONULL, _T(""));
                   ret=acedGetPoint(NULL,_T("\n指定第二个打断点:"),pt2);
                   if (ret!=RTNORM)
                      break;
                   breakCurve(pCurve,asPnt3d(pt1), asPnt3d(pt2));
                   break;
               case RTNONE:
                   breakCurve(pCurve,asPnt3d(pt1));
                   break;
                case RTNORM:
                   breakCurve(pCurve,asPnt3d(pt1), asPnt3d(pt2));
                    break;
              default:
                   break;
           }
        }
     }
     pEnt->close();
 }


 //以下为函数
 //打断于点
 bool breakCurve(AcDbCurve* curve,AcGePoint3d pt)
 {
     AcGePoint3d p1;
     curve->getClosestPointTo(pt,p1);
     double param;
     curve->getParamAtPoint(p1,param);
     AcGeDoubleArray params;
     params.append(param);
     AcDbVoidPtrArray curveSegments;
     curve->getSplitCurves(params, curveSegments);
     AcDbEntity* ent =NULL;
     if (curveSegments.length()==2)
     {
         ent=(AcDbEntity*)curveSegments[0];
         drawEntity(ent);
         ent->close();
         ent=(AcDbEntity*)curveSegments[1];
         drawEntity(ent);
         ent->close();
         curve->erase();
     }
     else
     {
         curve->close();
     }   
     return true ;
 }
 //两点打断
 bool breakCurve(AcDbCurve* curve, AcGePoint3d p1, AcGePoint3d p2)
 {
     AcGePoint3d p11;
     curve->getClosestPointTo(p1,p11);
     double param1;
     curve->getParamAtPoint(p11,param1);
     AcGePoint3d p21;
     curve->getClosestPointTo(p2,p21);
     double param2;
     curve->getParamAtPoint(p21,param2);
     AcGeDoubleArray params;
     if (param1<param2)
     {
         params.append(param1);
         params.append(param2);
     }
     else
     {
         params.append(param2);
         params.append(param1);
     }
     AcDbVoidPtrArray curveSegments;
     curve->getSplitCurves(params, curveSegments);
     AcDbEntity* ent =NULL;
     if (curveSegments.length()==2)
     {
         ent=(AcDbEntity*)curveSegments[1];
         drawEntity(ent);
         ent->close();
     }
     else if (curveSegments.length()==3)
     {
         ent=(AcDbEntity*)curveSegments[0];
         drawEntity(ent);
         ent->close();
         ent=(AcDbEntity*)curveSegments[2];
         drawEntity(ent);
         ent->close();
     }
     curve->erase();
     return true ;
 }
 //绘制打断的曲线
 void drawEntity(AcDbEntity* pEntity)
 {
     AcDbBlockTable *pBlockTable;
     acdbHostApplicationServices()->workingDatabase()
         ->getSymbolTable(pBlockTable, AcDb::kForRead);
     AcDbBlockTableRecord *brec;
     resbuf tilemode;
     acedGetVar(_T("TILEMODE"),&tilemode);
     int tile=tilemode.resval.rint;
     if (tile)
         pBlockTable->getAt(ACDB_MODEL_SPACE, brec,AcDb::kForWrite);
     else
         pBlockTable->getAt(ACDB_PAPER_SPACE, brec,AcDb::kForWrite);
     pBlockTable->close();
     AcDbObjectId entid;
     brec->appendAcDbEntity(entid, pEntity);
      brec->close();     
  }

【转载】曲线打断、求交点

原文：https://www.cnblogs.com/mjgw/p/12347934.html