ARX 沿着多段线绘制一定距离，递归执行

//from:起点，to:终点（这两点要相邻）
//paramDis:沿着多段线画多长
//pl:多段线
//pPoly:新的多段线
static void DrawByLen(const bool& gotoNext ,const AcGePoint2d& from,const AcGePoint2d& to,const double& paramDis,const AcDbPolyline* pl,AcDbPolyline* pPoly,int& polyIndex)
{
if(paramDis <= 0)
{
return;
}
int len = pl->numVerts();

AcGeCircArc2d arc2d;
AcGeLineSeg2d line2d;


AcGePoint2d ptS;
AcGePoint2d ptE;
bool isFind = false;
int plIndex = 0;
AcGeCurve2d* pCurve = NULL;

for(int i = 0;i < len;i++)
{
AcDbPolyline::SegType st = pl->segType(i);

if(st == AcDbPolyline::SegType::kArc)
{
pl->getArcSegAt(i,arc2d);
pCurve = &arc2d;
}
else if(st == AcDbPolyline::SegType::kLine)
{
pl->getLineSegAt(i,line2d);
pCurve = &line2d;
}


if(!pCurve->hasStartPoint(ptS) || !pCurve->hasEndPoint(ptE))
{
continue;
}

if(ptS == from && ptE == to || ptS == to && ptE == from)
{
plIndex = i;
isFind = true;
break;
}
}


double sumDis = 0.0;
if(isFind)
{
DrawIt(gotoNext,pl,paramDis,from,polyIndex,plIndex,sumDis,pPoly);
}
else
{
acutPrintf(_T("\nnot found"));
}
}


//summary
//指定一个起点和一条多段线，沿着多段线画出指定距离，递归执行，每次往后（前）移动一个点，直到画完指定的距离，
//pl:多段线
//paramDis:画多长
//ptStart:起始点
//polyIndex:添加到第几个了
//plIndex，遍历到多段线第几条线
//isSToE，遍历的顺序1：从前向后  0：从后向前
//sumDis，目前画的总长度
//pPoly:画出来的多段线
static void DrawIt(const bool& gotoNext,const AcDbPolyline* pl,const double& paramDis,const AcGePoint2d& ptStart,int& polyIndex,int& plIndex,double& sumDis,AcDbPolyline* pPoly)
{

AcDbPolyline::SegType st = pl->segType(plIndex);
AcGePoint2d ptS;
AcGePoint2d ptE;
double leftDis = 0.0;
double curveDis = 0.0;
double bulge = 0.0;
AcGeCurve2d* pCurve = NULL;
AcGeCircArc2d arc2d;
AcGeLineSeg2d line2d;
int len = pl->numVerts();


if(polyIndex == 2*(len - 2))
{
acutPrintf(_T("\nend poly is %d"),polyIndex);
return;
}


if(st == AcDbPolyline::SegType::kArc)
{
pl->getArcSegAt(plIndex,arc2d);
pCurve = &arc2d;！！！注意：指针的生命周期一定要大于等于指向的变量的生命周期，否则变量release掉指针就空了，再次使用指针程序直接崩溃！！
}
else if(st == AcDbPolyline::SegType::kLine)
{
pl->getLineSegAt(plIndex,line2d);
pCurve = &line2d;
}
if(!pCurve->hasStartPoint(ptS) || !pCurve->hasEndPoint(ptE))
{
return;
}
curveDis = pCurve->length(pCurve->paramOf(ptS),pCurve->paramOf(ptE));
leftDis = paramDis - sumDis;


pl->getBulgeAt(plIndex,bulge);


if(curveDis > leftDis)
{
double paramEnding = 0.0;

if(gotoNext)
{
AcGePoint2d ptEnding;
AcGePoint2d ptS;
pCurve->hasStartPoint(ptS);
GetPtAtDistOnCurve(pCurve,ptS,leftDis,ptEnding,Adesk::kTrue);


bulge = tan(atan(bulge) * leftDis/curveDis);


pPoly->addVertexAt(polyIndex,ptS,bulge);
polyIndex ++;
pPoly->addVertexAt(polyIndex,ptEnding);
}
else
{
AcGePoint2d ptEnding;
AcGePoint2d ptE;
pCurve->hasEndPoint(ptE);
GetPtAtDistOnCurve(pCurve,ptE,leftDis,ptEnding,Adesk::kFalse);


bulge = tan(atan(bulge) * leftDis/curveDis);


pPoly->addVertexAt(polyIndex,ptE,-bulge);
polyIndex ++;
pPoly->addVertexAt(polyIndex,ptEnding);
}
return;
}
else
{
if(gotoNext)
{
pPoly->addVertexAt(polyIndex,ptS,bulge);
polyIndex ++;
pPoly->addVertexAt(polyIndex,ptE);
polyIndex ++;
//acutPrintf(_T("\nplIndex is %d,poly is %d。is goto next,bulge is %.2f"),plIndex,polyIndex,bulge);
}
else
{
pPoly->addVertexAt(polyIndex,ptE,-bulge);
polyIndex ++;
pPoly->addVertexAt(polyIndex,ptS);
polyIndex ++;

}
/*acutPrintf(_T("\nptS[X] :%.2f,ptS[Y]:%.2f,ptE[X]:%.2f,ptE[Y]:%.2f"),ptS[X],ptS[Y],ptE[X],ptE[Y]);*/
sumDis += curveDis;

}


if(gotoNext)
{
plIndex = plIndex < len - 1  ? ++plIndex : 0;
}
else
{
plIndex = plIndex > 0 ? --plIndex : len - 1;
}


DrawIt(gotoNext,pl,paramDis,ptStart,polyIndex,plIndex,sumDis,pPoly);


}

反回曲线上一定距离的点（默认从起点开始计算）
pCurve:曲线指针，dist：距离，point：要返回的点
Adesk::Boolean isGotoNext  true:沿着正向寻找，false：沿着反方向寻找
static void GetPtAtDistOnCurve(const AcGeCurve2d* pCurve,const AcGePoint2d& ptInput,double dist,AcGePoint2d& point,Adesk::Boolean isGotoNext)
{
if(pCurve == NULL)
{
return;
}
AcGePoint2d ptS;
ptS = ptInput;
double pa = 0.0;
double datumParam = 0.0;
//Adesk::Boolean posParamDir = Adesk::kTrue;

datumParam = pCurve->paramOf(ptS);
pa = pCurve->paramAtLength(datumParam,dist,isGotoNext);
point = pCurve->evalPoint(pa);
}