绘制样条线.

[helpstring("method DrawSpline")]
HRESULT DrawSpline([in] IMxDrawPoints* points, [in] DOUBLE dStartTangentX, [in] DOUBLE dStartTangentY, [in] DOUBLE dEndTangentX, [in] DOUBLE dEndTangentY, [out,retval] VARIANT_BOOL* pRet);