Can someone explain what TikZ Calendar code is doing step by step?

Question

I am baffled by some Jedi Master code. This impressive calendar code would be nice to grasp. I can manipulate it by trial and error, but I would like to move to the next level and understand it. Obviously, the LaTeX3 / expl3 code is lengthy and probably too much for an answer to handle, but an explanation of the following questions and the pgf code used in alignment would be an acceptable answer.

• Calendar in LaTeX

What are the following:

• \pgfmathsetlength{\pgf@ya}{\tikz@lib@cal@yshift}

• \pgfmathsetlength\pgf@xa{\tikz@lib@cal@xshift}

Why is this code used instead of minimum height and minimum width of nodes:

• \pgfkeys{/tikz/day xshift=\cellwidth+2mm+2mm} % Set width of days
• \pgfkeys{/tikz/day yshift=\cellheight+2mm+2mm} % Set height of days

Why is there:

• \pgfkeys{/tikz/inner sep = 0pt}

yet day code node contains inner sep=1mm and adding \pgfkeys{/tikz/outer sep = 0pt} has no affect.

What defines the vertical spacing above the calendar? What if I have multiple rows for the day labels (multiple languages for the day names)? How do I ensure no overlap with the month name and calendar?

Confusing Code

I added the comments, so if they are incorrect, you will know why. These two code blocks seem to make the magic happen:

%% Adapted from https://tex.stackexchange.com/a/10199/4771
\makeatletter%
\tikzoption{day headings}{\tikzstyle{day heading}=[#1]}
\tikzstyle{day heading}=[]
\tikzstyle{day letter headings}=[
    execute before day scope={ \ifdate{day of month=1}{%
      \pgfmathsetlength{\pgf@ya}{\tikz@lib@cal@yshift}% 
      \pgfmathsetlength\pgf@xa{\tikz@lib@cal@xshift}%tikz@lib@cal@width effectively a multiple of day xshift
      \pgftransformyshift{-\pgf@ya}
      \foreach \d/\l in {0/Mantig,1/Dienstig,2/Mittwoch,3/Pfingstig,% Translate weekday names (start of week: Monday)
                         4/Freitig,5/Samstig,6/Sunntig} {
        \pgf@xa=\d\pgf@xa%
        \pgftransformxshift{\pgf@xa-\cellwidth/2}% Spread weekdays horizontally across calendar
        \pgftransformyshift{\pgf@ya}% Drop other weeks vertically so that first week is on first line.
        \node[above=-0.5ex,day heading]{\l};%
      }
    }{}%
  }%
]
\makeatother%

Or

\makeatletter
\tikzstyle{month label above centered}=[% Formatting of Month Name Location on Page
  execute before day scope={%
    \ifdate{day of month=1}{% Alignment of first day
      {
        \pgfmathsetlength{\pgf@xa}{\tikz@lib@cal@xshift}% Grab total width
        \pgf@xb=\tikz@lib@cal@width\pgf@xa% Set @xb to total width 
        \advance\pgf@xb by-\pgf@xa% Subtract full width from xb?
        \pgf@xb=.5\pgf@xb% Get half of xb?
        \pgftransformxshift{\pgf@xb}% 
        \pgftransformxshift{-\cellwidth/2}%
        \pgfmathsetlength{\pgf@y}{\tikz@lib@cal@yshift}%
        \pgftransformyshift{0.333\pgf@y}
        \tikzmonthcode%
      }
    }{}},
  every month/.append style={anchor=base}
]
\makeatother

/tikz/day code (slightly more understandable)

This fit business does not seem so elegant.

\pgfkeys{/tikz/day code =
  {
    \node (lower right) at (0,0) [above left,font=\Huge] {\tikzdaytext}; % Date label on each day
    \node (upper left) at (-\cellwidth,\cellheight) [below right,align=left,text width=\cellwidth-\pgflinewidth,font=\tiny,black] {\showtext}; % Adds week numbers
    \node (lower left) at (-\cellwidth,0) {};
    \node[draw, % day node
          fit=(lower right) (upper left) (lower left),
          inner sep=1mm,outer sep=0pt] {};
  }
}

If I replace all the day code nodes with just this node:

\node[draw,minimum width=\cellwidth,minimum height=\cellheight,outer sep=0pt,inner sep=0pt] {}; % Day Box

the boxes seem to be shifted horizontally by some space. Why is that? How can I make the distance between nodes 0pt such that the calendar looks like:

Full Code

See https://tex.stackexchange.com/a/170474/13552

Additional Relevant Links

• https://tex.stackexchange.com/a/10199/13552
• Weekday captions with the TikZ library "calendar"

Answer 1

Add Day Labels (day letter headings)

To do this, we need

• width of day (day xshift)
• height of day (day yshift)

A loop makes sense for this

\foreach \d/\l in {0/Monday,1/Tuesday,2/Wednesday,3/Thursday,
                4/Friday,5/Saturday,6/Sunday} {---Create node---}
                

The node could look like this:

    \node[above=-0.5ex,day heading,text width=\cellwidth,align=center]{\l};
    

(I swapped out above=-0.5ex with anchor=south)

The \d stores 0 thru 6. We use this to multiple times width of each day. e.g. 0 multiplied by a width of a day would equal zero, so in other words don't shift that day. The next day of the week (Tuesday in this example) should not overlap Monday, so it is shifted by 1 length (width of day). The third day (Wednesday) is shifted by 2 * "width of day" and so forth.

Prevent Day Lables from Overlapping Horizontally

We adjust each node's location using PGF Relative Coordinate Transformations (p. 1046).

What are \pgf@ya and \pgf@xa?

These are temporary TeX-dimensions (p. 751). They can be used to store numbers used in calculations for node placement. We can use these variables to store the global "width of day" and "height of day" variables for our equation that implements the aforementioned day alignment calculations.

You can set \pgf@ya and \pgf@xa using the syntax: \pgfmathsetlength{\pgf@ya}{---DIMENSION---} (dimension is a value + unit e.g. 3ex)

Behind the scenes: The TikZ calendar library (tikzlibrarycalendar.code.tex) sets these dimensions:

\def\tikz@lib@cal@yshift{3ex}
\def\tikz@lib@cal@xshift{3.5ex}

xshift extends the node to the left of the origin.

The keys day xshift and day yshift redefine these values, respectively. (\tikzoption{day xshift}{\def\tikz@lib@cal@xshift{#1}} & \tikzoption{day yshift}{\def\tikz@lib@cal@yshift{#1}})

Shift the days

To move the day label nodes in the loop, we need to first grab the "width of height" and "width of day" variables and assign them to \pgf@ya and \pgf@xa so that we can do some arithmetic with them.

\pgfmathsetlength{\pgf@ya}{\tikz@lib@cal@yshift}
\pgfmathsetlength{\pgf@xa}{\tikz@lib@cal@xshift}

The following is just multiplying the \d value in our loop above times the "width of day" variable to implement everthing explained in Section "Apply Day Labels".

\pgf@xa=\d\pgf@xa

The next step is to shift the nodes to the right for each day of the week in the loop. At first, you might think to use the following code:

\pgftransformxshift{\pgf@xa}

Remember that the width of each day was extended left from the day's origin. This means that the nodes will be aligned at the origins of each day (misaligned at the right-hand side) and not in the middle of the days.

%\pgftransformxshift{originshift - width of the day/2}
\pgftransformxshift{\pgf@xa-\tikz@lib@cal@xshift/2}

Except for some reason, TikZ cannot do arithmetic with \tikz@lib@cal@xshift, so the author decided to do this:

• initialize a length (\newlength{\cellwidth} and set it \setlength{\cellwidth}{\dimexpr\textwidth/7})
• assign \tikz@lib@cal@xshift to that length \pgfkeys{/tikz/day xshift=\cellwidth} % Set width of days
• use that length for this calculation

Like so:

\pgftransformxshift{\pgf@xa-\cellwidth/2}

The value of \cellwidth is also used to set the text width of each node.

Prevent Days from Overlapping Vertically

The corresponding vertical shifts are set like this:

\pgfkeys{/tikz/day yshift=\cellheight} % Set height of days
\newlength{\cellheight}
\setlength{\cellheight}{26mm}

Each node will be vertically aligned with the origin of the day where it was called (should be called once per month—first day of month)

One solution is to just move the labels one "height of day" above the origin of the day (day 1).

\pgftransformyshift{\pgf@ya}

You might be like me and wonder why you can't just use the calc library and do a anchor=south like this: \node[anchor=south] at (\pgf@xa-\cellwidth/2,0) + (0,1cm) {\l};. The truth is, I haven't tried this. I am just trying to understand the code that has been given before I explore this possibility.

Finish Things Up

The day labels should only be triggered once per month, so it can be hooked to day 1 with an if/then statement.

\ifdate{day of month=1}{---AFOREMENTIONED STUFF---}

We want this to be executed within the scope of the whole calendar (I think), so you need to wrap all of that with:

execute before day scope={---AFOREMENTIONED STUFF---}

Then we have to make this a style that we can call within the \calendar command, so we wrap EVERYTHING in a tikz style:

\tikzstyle{day letter headings}=[---AFOREMENTIONED STUFF---]

Finally, all of these needs to be wrapped with the following because TikZ uses the @ sign for it's macros.

\makeatletter
\makeatother

Typeset Calendar (\calendar[])

To use the calendar command using day letter headings:

The day code key can customize how days are drawn and needs to be used to ensure alignment. I am still learning about this.

Behind the scenes: The TikZ calendar library (tikzlibrarycalendar.code.tex) sets this:

\tikzoption{day code}{\def\tikzdaycode{#1}}


\calendar[
    dates=2016-01-01 to 2016-01-last,
    week list,
    day headings={font=\footnotesize},
    day letter headings,
    day code={
        \node [anchor=base east,draw,minimum width=\cellwidth,minimum height=\cellheight] (daybox) {}; % Draw the Day Boxes Using anchor=base east (causes the xshift to move left)
        \node[name=\pgfcalendarsuggestedname,every day,anchor=north east,font=\huge] at (daybox.north east) {\tikzdaytext}; % Date Number
        \node (upper left) at (-\cellwidth,\cellheight) [anchor=north west,align=left,text width=\cellwidth-\pgflinewidth,font=\tiny,black]  at (daybox.north west){\showtext}; % Week Day
        },
]

The parameters of day headings will be passed to the day heading style, which is used by the day label nodes.

Other Stuff

What is the every day key in the date number node?

Behind the scenes: The TikZ calendar library (tikzlibrarycalendar.code.tex) sets this:

\tikzoption{days}{\tikzstyle{every day}+=[#1]}
\tikzstyle{every day}=[anchor=base east]

What is the key name=\pgfcalendarsuggestedname?

---

Add Month Label (month label above centered)

---Answer unfinished--- more to come…