Filling of diagrams using tikzcd

Question

I have the following diagram:

\begin{tikzcd}[ampersand replacement=\&]
   x \arrow[rr] \arrow[dr] \&  \& y \arrow[dl]  \\ 
    \& z \&   \\
\end{tikzcd}

and I would like to use:

\fill[pattern=north east lines, pattern color=blue],

to fill it with that pattern. What is the correct way to do this? I am just getting errors every time I try this.

Answer 1

I think it's ugly-looking, however, if this is what you want...

You can use the fit library and execute at end picture option:

\documentclass{article}
\usepackage{tikz-cd}
\usetikzlibrary{fit, patterns}

\begin{document}
    \[
    \begin{tikzcd}[ampersand replacement=\&, execute at end picture={ 
      \node[rectangle, draw, blue,
                pattern=north east lines, pattern color=blue,
                fit={(tikz@f@1-1-1) (tikz@f@1-1-3)  (tikz@f@1-2-2)}
            ] 
        {};
        }  
      ]
    x \arrow[rr] \arrow[dr] \&  \& y \arrow[dl]  \\ 
    \& z \&   \\
    \end{tikzcd}
    \]
\end{document}

And if someone would like the pattern in the background:

\documentclass{article}
\usepackage{tikz-cd}
\usetikzlibrary{fit, patterns, backgrounds}

\begin{document}
    \[
    \begin{tikzcd}[ampersand replacement=\&, execute at end picture={ 
      \begin{scope}[on background layer] 
      \node[rectangle, draw, blue,
                pattern=north east lines, pattern color=blue,
                fit={(tikz@f@1-1-1) (tikz@f@1-1-3)  (tikz@f@1-2-2)}
            ] 
        {};  
      \end{scope}}]
    x \arrow[rr] \arrow[dr] \&  \& y \arrow[dl]  \\ 
    \& z \&   \\
    \end{tikzcd}
    \]
\end{document}

Note: The original version of this answer used overlay but it is not needed and caused vartical overlay with the text:

\documentclass{article}
\usepackage{tikz-cd}
\usetikzlibrary{fit, patterns}
\usepackage{mwe}
\begin{document}
\blindtext
    \[
    \begin{tikzcd}[remember picture, overlay, ampersand replacement=\&]
    x \arrow[rr] \arrow[dr] \&  \& y \arrow[dl]  \\ 
    \& z \&   \\
    \end{tikzcd}
    \tikz[remember picture, overlay]{
        \node[rectangle, draw, blue,
                pattern=north east lines, pattern color=blue,
                fit={(tikz@f@1-1-1) (tikz@f@1-1-3)  (tikz@f@1-2-2)}
            ] 
        {};
    }
    \]
\blindtext
\end{document}

Answer 2

I could be tempted to close as duplicate of the question you referred to in the first question you posted about this: tikz-cd: Shade faces of commutative cube

This is basically the same as what is described in the last part of Gonzalo's answer, but using your \fill command instead.

\documentclass[border=5mm]{standalone}
\usepackage{tikz-cd}
\usetikzlibrary{patterns,backgrounds}
\begin{document}

\begin{tikzcd}[
  ampersand replacement=\&,
  execute at end picture={
    \scoped[on background layer]
    \fill[pattern=north east lines, pattern color=blue] (a.center) -- (b.center) -- (c.center) -- cycle;
  }]
   |[alias=a]|x \arrow[rr] \arrow[dr] \&  \& |[alias=b]|y \arrow[dl]  \\ 
    \& |[alias=c]|z \&   
\end{tikzcd}
\end{document} 

Answer 3

As suplement to the first solution of the CarLaTeX answer. Small variations are:

• style for node with pattern is defined by the \tikzset
• for pattern is used pattern.meta packages,
• defined is matrix name

\documentclass{article}
\usepackage{tikz-cd}
\usetikzlibrary{fit,
                patterns.meta,
                shapes.geometric}
\tikzset{
F/.style = {draw=blue, inner ysep=0pt, fit=#1,
            postaction={pattern={Lines[angle=45,distance={2pt},
                                       line width=0.25pt]},
                        pattern color=blue!50, semitransparent} }
        }
\usepackage{lipsum}

\begin{document}
\lipsum[65]
\[
    \begin{tikzcd}[
every matrix/.append style = {name=m},
execute at end picture = {
    \node[F = (m-1-1) (m-1-3) (m-2-2) ] {};
                        }% end of execute at end picture
                    ]
x \ar[rr] \ar[dr]   &   & y \ar[dl] \\
                    & z &        
    \end{tikzcd}
\]
\lipsum[66]
\end{document}