Weird tikz text/inner sep positioning behaviour

Question

I've used the following SE answer to try to center the text in the left half or right half of a node. The left half is placed OK, but the right half is acting weird, and I haven't figured out why.

MWE:

\documentclass[tikz,border=1cm]{standalone}
\usepackage{standalone}
\usepackage{tikz}
\begin{document}
\newcommand{\textlabel}[3]{\node[label, inner xsep=\LabelSize/2, fill=#2] at (0,2*#1) {#3};}

\newcommand{\textlefthalf}[2]         {\textlabel{#1}{#2}{\hspace*{-\LabelSize}1}}
\newcommand{\textrighthalf}[2]        {\textlabel{#1}{#2}{\hspace*{\LabelSize}1}}
\newcommand{\textrighthalfalt}[2]     {\textlabel{#1}{#2}{1\hspace*{-\LabelSize}}}
\newcommand{\textrighthalfaltcolor}[2]{\textlabel{#1}{#2}{\color{white}1\hspace*{-\LabelSize}}}


\newlength\LabelSize
\setlength\LabelSize{1cm}

\tikzset{
    label/.style={fill=black,text width=\LabelSize, align=center,minimum height=\LabelSize,minimum width=\LabelSize*2,inner sep=0em,text=white,font=\sffamily\fontsize{15pt}{0pt}\selectfont},
}    
\begin{tikzpicture}
\textlefthalf{0}{blue}
\textrighthalf{1}{red}
\textrighthalfalt{2}{black}
\textrighthalfaltcolor{3}{gray}
\draw[dashed] (0,-1) -- (0,7);
\draw[green, dashed] (-\LabelSize/2,-1) -- (-\LabelSize/2,7);
\draw[green, dashed] (\LabelSize/2,-1) -- (\LabelSize/2,7);    
\end{tikzpicture}

\end{document}

Blue is okay, right is off-'centre', black is centered to the real center (not the one I intend). The gray one is the one I want to see. But why does adding the \color{white} help to achieve this?

I'd like to understand what's happening so that I can tune my mental model of latex.

Answer 1

If you look carefully, you'll see that the "not working" part is the only one containing a positive \hspace. You have set text width=\LabelSize and put a horizontal space of the same width in it. So, the box is full: everything after that space, runs out of the box. I used a \rule to show that.

Instead, using negative spaces to position boxes can work quite well, as you have seen, but one has to carefully figure out, what you actually are doing. To properly get what you want, you can use another negative space, but in order to show its effect, there has to be any box after it. Else this space is not recognized. So I put a \null there:

\documentclass[tikz,border=1cm]{standalone}
\usepackage{standalone}
\usepackage{tikz}
\begin{document}
\newcommand{\textlabel}[3]{\node[label, inner xsep=\LabelSize/2, fill=#2] at (0,2*#1) {#3};}

\newcommand{\textlefthalf}[2]    {\textlabel{#1}{#2}{\hspace*{-\LabelSize}1}}
\newcommand{\textrighthalf}[2]   {\textlabel{#1}{#2}{\rule{\LabelSize}{1pt}1}}
\newcommand{\textrighthalfalt}[2]{\textlabel{#1}{#2}{1\hspace*{-\LabelSize}\null}}

\newlength\LabelSize
\setlength\LabelSize{1cm}

\tikzset{
    label/.style={fill=black,text width=\LabelSize, align=center,minimum height=\LabelSize,minimum width=\LabelSize*2,inner sep=0em,text=white,font=\sffamily\fontsize{15pt}{0pt}\selectfont},
}    
\begin{tikzpicture}
\textlefthalf{0}{blue}
\textrighthalf{1}{red}
\textrighthalfalt{2}{black}
\draw[dashed] (0,-1) -- (0,5);
\draw[green, dashed] (-\LabelSize/2,-1) -- (-\LabelSize/2,5);
\draw[green, dashed] (\LabelSize/2,-1) -- (\LabelSize/2,5);    
\end{tikzpicture}

\end{document}

Answer 2

This is not an answer to your question but an alternative method to achieve what you seem to want. (The shapes.multiparts is not essential but may be useful in case you want to access the various parts.) Of course, one could write macros for these things.

\documentclass[tikz,border=1cm]{standalone}
\usepackage{tikz}
\usetikzlibrary{shapes.multipart}
\begin{document}
\newlength\LabelSize
\setlength\LabelSize{1cm}

\begin{tikzpicture}[font=\sffamily\fontsize{15pt}{0pt}\selectfont]
\node[rectangle split, rectangle split parts=2,rectangle split
horizontal,fill=blue,text=white,rectangle split part align={center,center},
inner sep=0pt,minimum height=1cm] 
at (0,0) {\makebox[1cm][c]{1}\nodepart{two}\makebox[1cm][c]{}}; 
\node[rectangle split, rectangle split parts=2,rectangle split
horizontal,fill=red,text=white,rectangle split part align={center,center},
inner sep=0pt,minimum height=1cm] 
at (0,2) {\makebox[1cm][c]{}\nodepart{two}\makebox[1cm][c]{1}}; 
\node[fill=black,text=white,minimum width=2*\LabelSize,
inner sep=0pt,minimum height=1cm] 
at (0,4) {1}; 
\draw[dashed] (0,-1) -- (0,5);
\draw[green, dashed] (-\LabelSize/2,-1) -- (-\LabelSize/2,5);
\draw[green, dashed] (\LabelSize/2,-1) -- (\LabelSize/2,5);    
\end{tikzpicture}
\end{document}