algorithm2e and color

Question

I am trying to color the background of the caption in algorithm (using algorithm2e).

I have modified the original command as follow directly in the .sty file.

However, as you can see on the image, the result is not convenient. I would like the whole "row" to be in gray (I put row into brackets as it is not a tabular).

\newcommand{\algocf@makecaption@ruled}[2]{%
  \global\sbox\algocf@capbox{\hskip\AlCapHSkip![enter image description here][2]
    \parbox[t]{\hsize}{\colorbox{gray!50}{\algocf@captiontext{#1}{#2}}}}
}%

The original :

\newcommand{\algocf@makecaption@ruled}[2]{%
  \global\sbox\algocf@capbox{\hskip\AlCapHSkip% .5\algomargin%
    \parbox[t]{\hsize}{\algocf@captiontext{#1}{#2}}}
}%

The complete code :

\documentclass{article} 
\usepackage{etex} 
\usepackage{easybmat} 
\usepackage[T1]{fontenc} 
\usepackage{lmodern} 
\usepackage{xcolor}
\usepackage{algorithm2e}
\RestyleAlgo{algoruled}

\begin{document} 

  \SetKw{KwFrom}{from} 


\newenvironment{algo}{
\begin{algorithm}[H]
\DontPrintSemicolon \SetAlgoVlined}
{\end{algorithm}}



\begin{algo}\label{algotrigsup}
\caption{Caption of the algo}
\For{$k$ \KwFrom $n-1$ \KwTo $1$}{
$x_k=b_k$\;
\For{$j$ \KwFrom $k+1$ \KwTo $n$}{
$x_k=x_k -a_{kj} x_j$\;
}
$x_k=\displaystyle \frac{x_k}{a_{kk}}$
}
\end{algo}


\end{document}

Answer 1

Here's one possibility (the \parbox has to be inside the \colorbox and some vertical and horizontal spacing adjustments are required):

\documentclass{article}
\usepackage[ruled]{algorithm2e}
\usepackage{xcolor}

\colorlet{AlgCaptionColor}{gray!30}

\makeatletter
\renewcommand{\algocf@makecaption@ruled}[2]{%
  \global\sbox\algocf@capbox{\colorbox{AlgCaptionColor}{\hskip\AlCapHSkip% .5\algomargin%
    \parbox[t]{\hsize}{\algocf@captiontext{\strut#1}{\strut#2\strut}}\hskip.6\algomargin}}% then caption is not centered
}%
\setlength{\interspacetitleruled}{0pt}%
\makeatother

\begin{document}

\begin{algorithm}[H]
\SetAlgoLined
\KwData{this text}
\KwResult{how to write algorithm with \LaTeX2e }
initialization\;
\While{not at end of this document}{
read current\;
\eIf{understand}{
go to next section\;
current section becomes this one\;
}{
go back to the beginning of current section\;
}
}
\caption{How to write algorithms and some additional text just for the exmaple}
\end{algorithm}

\end{document}