\documentclass[tikz,border=2bp]{standalone}
\usetikzlibrary{backgrounds,calc,trees,hobby}
\pgfdeclarelayer{background}
\pgfsetlayers{background,main}
\newcommand{\hobbyconvexpath}[2]{
[
create hobbyhullnodes/.code={
\global\edef\namelist{#1}
\foreach [count=\counter] \nodename in \namelist {
\global\edef\numberofnodes{\counter}
\node at (\nodename)
[draw=none,name=hobbyhullnode\counter] {};
}
\node at (hobbyhullnode\numberofnodes)
[name=hobbyhullnode0,draw=none] {};