pgfplots filling under spline

Question

Is there any way to fill the area under a spline? In the example below, removing mesh from the addplot options closes the cycle as expected with by joining the first and last coordinate by a straight line. How can the fill instead be to the axis?

\documentclass{standalone}
\usepackage{pgfplots}
\usepgfplotslibrary{patchplots}
\begin{document}
\begin{tikzpicture}
\begin{axis}
\addplot[patch,patch type=cubic spline]coordinates{(0,0)(3,1)(1,.5)(2,.5)};
\end{axis}
\end{tikzpicture}
\end{document}

Answer 1

A valid request. It is currently unsupported by pgfplots (which assumes that mesh plots introduce individually colored segments for which fill-against-axis is no use-case).

I accept this as a feature request. More precisely, future versions of pgfplots will draw one global path with a single color as soon as point meta=none is used to disable individually colored segments. The future version will support fill-against-axis by appending fill=blue and the suffix (2,.5)} \closedcycle;