Insert grid on tikz picture with standalone

Question

I'd like to insert a grid to fill the whole picture. I'm trying to mimic a blueprint paper.

So, I have two questions:

1. Why the use of colored rectangle change the border around picture?
2. Why the grid is much bigger than the picture size? In some sense, the anchors are not working.

Edit: using the current bounding box as suggested by Phelype Oleinik, the grid is over the draw. But the space around produced by the background rectangle is out of the grid.

MWE

% !TeX program = pdflatex
\documentclass[border=0]{standalone}
\usepackage{tikz}
\usetikzlibrary{backgrounds}
\begin{document}
\begin{tikzpicture}[
background rectangle/.style={fill=green},
show background rectangle, %% <-- insert space around
]
\draw (0,0) -- (3,4) -- (0,3) -- cycle;    

\draw[white,step=.5cm]   (current bounding box.south west) grid (current bounding box.north east);
\end{tikzpicture}
\end{document}

Answer 1

backgrounds library offers two option show background rectangle and show background grid (or gridded) which can be combined to obtain the desired result.

Initially separation between figure and background rectangle is .5ex, but tight background forces it to 0pt.

If background rectangle is filled, background grid should be drawn after it.

% !TeX program = pdflatex
\documentclass[border=0]{standalone}
\usepackage{tikz}
\usetikzlibrary{backgrounds}
\begin{document}
\tikzset{%
  mybackground/.style={%
    tight background, % 0pt margins around figure
    background rectangle/.style={fill=green},
    background grid/.style={draw=white, step=2mm, ultra thin},
    show background rectangle,
    show background grid % after a filled background rectangle
  }%
}%

\begin{tikzpicture}[mybackground]
\draw (0,0) -- (3,4) -- (0,3) -- cycle;
\end{tikzpicture}
\end{document}

Answer 2

The standalone class, by default, puts everything inside \begin{document}...\end{document} in an \hbox, then crops the page to the size of this \hbox. When you use the current page hook, the page is not yet cropped, so the full size is used.

Then, as I said in the comment, you can switch to the current bounding box hook, so the grid is drawn around the picture only, and the boxing of standalone is correct.

But then the grid does not span the whole page, just the picture because you used the show background rectangle option, which does:

\tikzstyle{show background rectangle}=[execute at end picture=\tikz@background@framed]

after the picture is created and the bounding box is set, so the current bounding box looks smaller than the "actual bounding box".

You can, however, tell TikZ to execute some piece of code after the picture is created. You just have to assure that the grid is drawn after the show background rectangle is executed:

% !TeX program = pdflatex
\documentclass[border=0]{standalone}
\usepackage{tikz}
\usetikzlibrary{backgrounds,calc}
\begin{document}
\tikzset{%
  blueprint/.style={%
    execute at end picture={%
      \begin{scope}[on background layer]
        \draw[white,step=.5cm] (current bounding box.south west) grid (current bounding box.north east);
      \end{scope}
    }%
  }%
}%
\begin{tikzpicture}[%
  inner frame sep = 0.5cm, % to make the grid match the border
  show background rectangle,%% <-- insert space around
  blueprint,% This MUST be after "show background rectangle"
  background rectangle/.style={fill=green},
  ]
\draw (0,0) -- (3,4) -- (0,3) -- cycle;
\end{tikzpicture}
\end{document}

Answer 3

Here is one solution.

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{backgrounds}
\begin{document}
\begin{tikzpicture}
\draw (0,0) -- (3,4) -- (0,3) -- cycle;    

\begin{scope}[on background layer]
\fill[green]   (current bounding box.south west) rectangle (current bounding box.north east);
\draw[white,step=.5cm]   (current bounding box.south west) grid (current bounding box.north east);
\end{scope}
\end{tikzpicture}
\end{document}