l3draw diagram as a background

Question

Consider the MWE below:

\documentclass{article}
\usepackage[vmargin=3cm]{geometry}
\usepackage{l3draw}
\usepackage{lipsum}
\ExplSyntaxOn

% Define color for notepad rules
\color_set:nnn {notepadrulecolor} { RGB } { 217, 244, 244 }

% Command to draw the notepad background
\cs_new_protected:Nn \draw_notepad_background:
{
  \draw_begin:
    \draw_linewidth:n { 1pt }
    \color_select:n { notepadrulecolor }
    \draw_path_moveto:n { 2cm, 2cm }
    \draw_path_lineto:n { 2cm , 27cm } 
    \draw_path_use_clear:n { stroke }
    
  \draw_end:
}

% Hook to draw background on every page
\AddToHook{shipout/background}
{
  \draw_notepad_background:
}

\ExplSyntaxOff

\begin{document}

\lipsum[1-14]

\end{document}

What I am currently trying to achieve is to draw a vertical line that spans the height of the page and is on the left margin of the text area. I know this can be done via TikZ but am trying to recreate it with l3draw. Any assistance would be appreciated.

Answer 1

You need to set the bounding box of the drawing to zero and then either shift it to the right position on the page or change the y values to negative (because positive values depict upwards and the drawing box will sit in the upper left corner of the page).

I changed the color to enhance the visibility of the line, feel free to revert:

\documentclass{article}
\usepackage[vmargin=3cm]{geometry}
\usepackage{l3draw}
\usepackage{lipsum}

\ExplSyntaxOn

% Define color for notepad rules
\color_set:nnn { notepadrulecolor } { RGB } { 0, 244, 244 }

% Command to draw the notepad background
\cs_new_protected:Nn \azetina_notepad_draw_background:
{
  \draw_begin:
    \bool_set_false:N \l_draw_bb_update_bool
    \draw_linewidth:n { 1pt }
    \color_select:n { notepadrulecolor }
    \draw_path_moveto:n { 2cm, -2cm }
    \draw_path_lineto:n { 2cm , -27cm } 
    \draw_path_use_clear:n { stroke }
  \draw_end:
}

% Hook to draw background on every page
\AddToHook{shipout/background}
{
  \azetina_notepad_draw_background:
}

\ExplSyntaxOff

\begin{document}

\lipsum[1-14]

\end{document}

Alternatively, use \draw_transform_shift:n { 0pt , -\paperheight } and keep the positive y values.

Answer 2

Since Jasper Habicht already provided an l3draw answer, here's a simpler approach which avoids the need for any additional package.

The shipout/background hook puts the specified code into a picture environment. Hence, for simple drawings, there is no need to use either tikz or l3draw. Instead, we can just use picture mode itself.

\put (2cm,\dimexpr 2cm-\paperheight) 
  {\color_select:n {notepadrulecolor} \line(0,1){27cm}}

• \put(<x>,<y>){<stuff>} is a picture-mode macro which typesets <stuff> at <x>,<y> relative to the lower-left corner of the page. So \put (2cm, \dimexpr 2cm-\paperheight) {...} puts {...} 2cm to the right and 2cm above the lower-left corner of the page.
• \line(<x>,<y>){<dim>} draws a line of <dim> length in the direction of the vector specified by <x>,<y>. So \line(0,1){27cm} draws a vertical line from the current point of 27cm.

I couldn't see the line clearly, so I changed the colour for purposes of testing and demonstration.

\documentclass{article}
\usepackage[vmargin=3cm]{geometry}
\usepackage{lipsum}
\ExplSyntaxOn

% Define color for notepad rules
% \color_set:nnn {notepadrulecolor} { RGB } { 217, 244, 244 }
\color_set:nnn {notepadrulecolor} { RGB } { 150, 200, 200 }

% Hook to draw background on every page
\AddToHook{shipout/background}
{
  \put (2cm,\dimexpr 2cm-\paperheight) 
  {\color_select:n {notepadrulecolor} \line(0,1){27cm}}
}

\ExplSyntaxOff

\begin{document}
\lipsum[1-14]
\end{document}