Bicolor text: height of expressions

Question

I'd like to put bicolored text. This is what I did

\newlength\myl
\newlength\myh
\newcommand{\bicolor}[1]{
\setlength{\myl}{0pt-\widthof{#1}}%
\setlength{\myh}{\heightof{#1}}%
\raisebox{0.5\myh}{\color{red}\clipbox{0pt  {0.5\myh} 0pt 0pt}{\mbox{#1}}}%
\hspace{\myl}%
{\color{blue}\clipbox{0pt  0pt 0pt {0.5\myh}}{\mbox{#1}}}%
}

and the \bicolor{BiKolor stuff}

kind of works... (some problems cutting at the end)

However, this does not work \bicolor{BiKolor$_2$}

What is a better way to proceed?

Answer 1

As already pointed out in this answer, the problem is that the depth is not taken into account. This answer also fixes the problem, but in a slightly different way than Steven: the height of the dividing line does not depend on the depth. Whether or not this is a good thing I do not know. Another difference is that spurious spaces get avoided (but this is not really essential).

\documentclass{article}
\usepackage{trimclip}
\usepackage{xcolor}
\newlength\myl
\newlength\myh
\newcommand{\bicolor}[1]{%
\setbox0\hbox{#1}%
\makebox[\wd0][c]{\raisebox{\dimexpr0.5\ht0-0.5\dp0}{\textcolor{red}{\clipbox{-1pt {\dimexpr0.5\ht0+0.5\dp0} -1pt -1pt}{\copy0}}}%
\hspace{\dimexpr-\wd0-2pt}%
{\textcolor{blue}{\clipbox{-1pt -1pt -1pt {0.5\ht0}}{\copy0}}}}%
}
\begin{document}
B\bicolor{BiKolor$_2$}B\bicolor{BiKolor stuff}\par
B{BiKolor$_2$}B{BiKolor stuff}
\end{document}

Answer 2

You need to account for the depth of the text below the baseline.

\documentclass{article}
\usepackage{xcolor,calc,trimclip}
\begin{document}
\newlength\myl
\newlength\myh
\newlength\myd
\newcommand{\bicolor}[1]{
\setlength{\myl}{0pt-\widthof{#1}}%
\setlength{\myh}{\heightof{#1}}%
\setlength{\myd}{\depthof{#1}}%
\raisebox{0.5\myh}{\color{red}\clipbox{0pt  {0.5\myh+\myd} 0pt 0pt}{\mbox{#1}}}%
\hspace{\myl}%
{\color{blue}\clipbox{0pt  0pt 0pt {0.5\myh}}{\mbox{#1}}}%
}

\bicolor{BiKolor stuff}

\bicolor{BiKolor$_2$}
\end{document}

Note that you lose a little bit of the "ff" font glyphs from clipping, because of font protrusion or "overshoot" (see What is the local height of a capital letter?). You can clip to -1pt on those boundaries to compensate, if desired.

However, if you clip -1pt on the left and right borders, it will make the result 2pt wider, so you need to \hspace leftwards 1pt at the start and end of the process. In the MWE, I show with and without bi-color to compare results.

\documentclass{article}
\usepackage{xcolor,calc,trimclip}
\newlength\myl
\newlength\myh
\newlength\myd
\newcommand{\bicolor}[1]{\hspace{-1pt}%
\setlength{\myl}{0pt-\widthof{#1}}%
\setlength{\myh}{\heightof{#1}}%
\setlength{\myd}{\depthof{#1}}%
\raisebox{0.5\myh}{\color{red}\clipbox{-1pt  {0.5\myh+\myd} -1pt -1pt}%
  {\mbox{#1}}}%
\hspace{\myl-2pt}%
{\color{blue}\clipbox{-1pt  -1pt -1pt {0.5\myh}}{\mbox{#1}}}%
\hspace{-1pt}}

\begin{document}
BiKolor stuff

\bicolor{BiKolor stuff}

\bicolor{BiKolor$_2$ Xg jRETY}

BiKolor$_2$ Xg jRETY
\end{document}