Combining shading and transparency in TikZ

Question

With this code:

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\fill[shading=radial] (0,5) circle (2);
\fill[top color=black] (5,3) rectangle (9,7);
\fill[shading=radial, ultra nearly transparent] (0,0) circle (2);
\fill[top color=black, ultra nearly transparent] (5,-2) rectangle (9,2);
\end{tikzpicture}
\end{document}

I get (pdf both with mac preview and Adobe Reader) :

Why does the transparent option almost(but not completely) remove the shading?

Where does the ultra thin perimeter line come from in a pure \fill (no \draw or \filldraw)?

Answer 1

You need \shade not \fill.

– percusse

Result: