AcDbCurve::extend 延长指定多义线的前后长度

int myExtendPolyline(AcDbPolyline* pl,double sOff,double eOff){ASSERT(pl);if (pl->numVerts() < 2){return 0;}if (sOff > 0){AcGePoint3d sPt,sPt2;pl->getStartPoint(sPt);pl->getPointAt(1,sPt2);double td1,td2;pl->getDistAtPoint(sPt,td1);pl->getDistAtPoint(sPt2,td2);double off = td2 - td1;double sParam = fabs(sOff) / off;if(pl->extend(-sParam) != Acad::eOk){ASSERT(0);return 0;}}if (eOff > 0){AcGePoint3d ePt,ePt2;pl->getEndPoint(ePt);pl->getPointAt(pl->numVerts() - 2,ePt2);double td1,td2;pl->getDistAtPoint(ePt2,td1);pl->getDistAtPoint(ePt,td2);double off = td2 - td1;double eparam = fabs(eOff) / off;if(pl->extend(eparam) != Acad::eOk){ASSERT(0);return 0;}}return 1;}