Distinguish forward cross-references from backward cross-references

Question

Andrew gave an answer to the question in How to refer to indexed words (which is working very, very nicely). As it happens, it allows referring forward to where the word will be defined as well as the usual backward. This is actually very helpful as when explaining at the beginning of a chapter what will be done, but would be even more helpful if one could differentiate forward from backward, say with a different hyperref color. Here is the MWF that Andrew answered modified to use hyperref color instead of boxes and with a reference forward.

    \documentclass[11pt]{book}
    \usepackage{makeidx}
    \makeindex
    \usepackage{tcolorbox}
%==================Begin HYPERREF
    \usepackage[hyperfootnotes=false]{hyperref}%[pdfborder={0 0 0}]

%Begin the ``quick and dirty hack'' due to Heiko Oberdiek which loads showidx
\makeatletter
\ifHy@hyperindex
  \def\HyInd@ParenLeft{(}%
% Hook in \HyInd@@wrindex
  \let\HyInd@showidx\@empty
% Hook in \HyInd@@wrindex for package showidx
  \def\HyInd@showidx#1{%
    \@showidx{#1}%
    \if@nobreak
      \ifvmode
        \nobrak
      \fi
    \fi
  }%
% Load package showidx
  \let\siOrg@makeindex\makeindex
  \let\siOrg@@index\@index
  \let\siOrg@@wrindex\@wrindex
  \let\siOrg@index\index
  \RequirePackage{showidx}
  \let\makeindex\siOrg@makeindex
  \let\@index\siOrg@@index
  \let\@wrindex\siOrg@@wrindex
  \let\index\siOrg@index
% rest of hyperref part
  \@ifpackageloaded{multind}{%
    \let\HyInd@org@wrindex\@wrindex
    \def\@wrindex#1#2{\HyInd@@wrindex{#1}#2||\\}%
    \def\HyInd@@wrindex#1#2|#3|#4\\{%
      \ifx\\#3\\%
        \HyInd@org@wrindex{#1}{#2|hyperpage}%
      \else
        \def\Hy@temp@A{#3}%
        \ifx\Hy@temp@A\HyInd@ParenLeft
          HyInd@org@wrindex{#1}{#2|#3hyperpage}%
        \else
          \HyInd@org@wrindex{#1}{#2|#3}%
        \fi
      \fi
    }%
  }{%
    \def\@wrindex#1{\@@wrindex#1||\\}
    \def\@@wrindex#1|#2|#3\\{%
      \ifx\\#2\\%
        \protected@write\@indexfile{}{%
          \string\indexentry{#1|hyperpage}{\thepage}%
        }%
      \else
        \def\Hy@temp@A{#2}%
        \ifx\Hy@temp@A\HyInd@ParenLeft
          \protected@write\@indexfile{}{%
             \string\indexentry{#1|#2hyperpage}{\thepage}%
          }%
        \else
          \protected@write\@indexfile{}{%
            \string\indexentry{#1|#2}{\thepage}%
          }%
        \fi
      \fi
      \endgroup
      \HyInd@showidx{#1}%
      \@esphack
    }%
  }%
\fi
\makeatother
%End the ``quick and dirty hack'' due to Heiko Oberdiek which loads showidx
    \hypersetup{%begin colors
                   colorlinks,
                   linkcolor={red!50!black},
                   citecolor={blue!50!black},
                  urlcolor={blue!80!black}
                }%end colors

    \usepackage{cleveref}
%Begin the Sharpe code as modified by Schulz (2016-02-1)
\let\oldopenparen\(
\let\oldcloseparen\)
\def\({\protect\oldopenparen}
\def\){\protect\oldcloseparen}
%End the Sharpe code as modified by Schulz (2016-02-1)

\newcommand{\INDEX}[2][]{%
\if\relax\detokenize{#1}\relax\index{#2}\label{ind:#2}%
   \else\index{#2}\label{ind:#1}\fi%
}
\newcommand{\DEX}[2][]{%
   \if\relax\detokenize{#1}\relax\hyperref[ind:#2]{#2} (\Cpageref{ind:#2})%
   \else\hyperref[ind:#1]{#2} (\Cpageref{ind:#1})\fi%
}%

\newcounter{abc}%
\newtcolorbox%
[%beginForReferences
use counter= abc,
number within=chapter,
number freestyle={\noexpand\thechapter.\noexpand\arabic{\tcbcounter}~\noexpand\mytitleagree},%Used to make for LONG titles in the references.
crefname={definition}{definitions},
Crefname={Definition}{Definitions},
]%endForReferences
{greement}
[2][]%
{%
detach title,
coltitle=black,
nameref={#2},%
before upper={\tcbtitle\quad},
code={\gdef\mytitleagree{#2}},%Used to make for LONG titles in the references.
title=DEFINITION \thetcbcounter,%
#1,%Required for references.
}%



    \begin{document}

A \textbf{minimum}\INDEX{minimum} of a function is blah blah.

And here is a reference ahead: \DEX[]{Carla}

\begin{greement}[label={abc:3-1}]{Maximum}
  An input whose output is larger than the outputs of nearby inputs
\end{greement}

\INDEX[pm]{$\pm$}
\newpage

A function can have more than one \DEX{minimum}.

A function can have more than one \DEX{minimum}.

\chapter{one} \textbf{Andy}\INDEX[]{Andy} \chapter{two} \textbf{Beth}\INDEX[]{Beth} \chapter{three} \textbf{Carla}\INDEX[]{Carla} \chapter`{four}` \DEX[]{Andy} \DEX[]{Beth} .

\printindex


    \end{document}

So, my question is: how can forward cross-references be made made to look different from backward cross-references?

Answer 1

As long as only the \DEX macro is used in order to generate references to the linked words, there is a quite simple way to distinguish between forward and backward links:

Check for the current page number and compare with the page reference of the linked word with \ifnum\value{page} > \getpagerefnumber{ind:#2}...\else...\fi.

In the first case we have a back reference, in the second case we have a forward reference, for references on the same page this will not work (yet), I will try to update later on (i.e. tomorrow) with a better version)

I've provided two new colors: forwardlinkcolor and backwardlinkcolor, change their definitions at will.

\newcommand{\DEX}[2][]{%
  \begingroup
  \ifnum\value{page} > \getpagerefnumber{ind:#2}%
  \hypersetup{%
    linkcolor=backwardlinkcolor
  }%
  \else
  \hypersetup{%
    linkcolor=forwardlinkcolor
  }%
  \fi
  \if\relax\detokenize{#1}\relax\hyperref[ind:#2]{#2} (\Cpageref{ind:#2})%
  \else\hyperref[ind:#1]{#2} (\Cpageref{ind:#1})\fi%
  \endgroup
}%

The full code:

\documentclass[11pt]{book}
\usepackage{makeidx}
\makeindex
\usepackage{tcolorbox}
% ==================Begin HYPERREF
\usepackage[hyperfootnotes=false]{hyperref}%[pdfborder={0 0 0}]

%Begin the ``quick and dirty hack'' due to Heiko Oberdiek which loads showidx
\makeatletter
\ifHy@hyperindex
  \def\HyInd@ParenLeft{(}%
% Hook in \HyInd@@wrindex
  \let\HyInd@showidx\@empty
% Hook in \HyInd@@wrindex for package showidx
  \def\HyInd@showidx#1{%
    \@showidx{#1}%
    \if@nobreak
      \ifvmode
        \nobrak
      \fi
    \fi
  }%
% Load package showidx
  \let\siOrg@makeindex\makeindex
  \let\siOrg@@index\@index
  \let\siOrg@@wrindex\@wrindex
  \let\siOrg@index\index
  \RequirePackage{showidx}
  \let\makeindex\siOrg@makeindex
  \let\@index\siOrg@@index
  \let\@wrindex\siOrg@@wrindex
  \let\index\siOrg@index
% rest of hyperref part
  \@ifpackageloaded{multind}{%
    \let\HyInd@org@wrindex\@wrindex
    \def\@wrindex#1#2{\HyInd@@wrindex{#1}#2||\\}%
    \def\HyInd@@wrindex#1#2|#3|#4\\{%
      \ifx\\#3\\%
        \HyInd@org@wrindex{#1}{#2|hyperpage}%
      \else
        \def\Hy@temp@A{#3}%
        \ifx\Hy@temp@A\HyInd@ParenLeft
          HyInd@org@wrindex{#1}{#2|#3hyperpage}%
        \else
          \HyInd@org@wrindex{#1}{#2|#3}%
        \fi
      \fi
    }%
  }{%
    \def\@wrindex#1{\@@wrindex#1||\\}
    \def\@@wrindex#1|#2|#3\\{%
      \ifx\\#2\\%
        \protected@write\@indexfile{}{%
          \string\indexentry{#1|hyperpage}{\thepage}%
        }%
      \else
        \def\Hy@temp@A{#2}%
        \ifx\Hy@temp@A\HyInd@ParenLeft
          \protected@write\@indexfile{}{%
             \string\indexentry{#1|#2hyperpage}{\thepage}%
          }%
        \else
          \protected@write\@indexfile{}{%
            \string\indexentry{#1|#2}{\thepage}%
          }%
        \fi
      \fi
      \endgroup
      \HyInd@showidx{#1}%
      \@esphack
    }%
  }%
\fi
\makeatother
%End the ``quick and dirty hack'' due to Heiko Oberdiek which loads showidx
\hypersetup{%begin colors
  colorlinks,
  linkcolor={red!50!black},
  citecolor={blue!50!black},
  urlcolor={blue!80!black}
}%end colors

\usepackage{cleveref}
%Begin the Sharpe code as modified by Schulz (2016-02-1)
\let\oldopenparen\(
\let\oldcloseparen\)
\def\({\protect\oldopenparen}
\def\){\protect\oldcloseparen}
%End the Sharpe code as modified by Schulz (2016-02-1)

\newcommand{\INDEX}[2][]{%
\if\relax\detokenize{#1}\relax\index{#2}\label{ind:#2}%
   \else\index{#2}\label{ind:#1}\fi%
}

\colorlet{forwardlinkcolor}{red!50!black}
\colorlet{backwardlinkcolor}{green!40!blue}

\newcommand{\DEX}[2][]{%
  \begingroup
  \ifnum\value{page} > \getpagerefnumber{ind:#2}%
  \hypersetup{%
    linkcolor=backwardlinkcolor
  }%
  \else
  \hypersetup{%
    linkcolor=forwardlinkcolor
  }%
  \fi
  \if\relax\detokenize{#1}\relax\hyperref[ind:#2]{#2} (\Cpageref{ind:#2})%
  \else\hyperref[ind:#1]{#2} (\Cpageref{ind:#1})\fi%
  \endgroup
}

\newcounter{abc}%
\newtcolorbox%
[%beginForReferences
use counter= abc,
number within=chapter,
number freestyle={\noexpand\thechapter.\noexpand\arabic{\tcbcounter}~\noexpand\mytitleagree},%Used to make for LONG titles in the references.
crefname={definition}{definitions},
Crefname={Definition}{Definitions},
]%endForReferences
{greement}
[2][]%
{%
detach title,
coltitle=black,
nameref={#2},%
before upper={\tcbtitle\quad},
code={\gdef\mytitleagree{#2}},%Used to make for LONG titles in the references.
title=DEFINITION \thetcbcounter,%
#1,%Required for references.
}%



\begin{document}

A \textbf{minimum}\INDEX{minimum} of a function is blah blah.

And here is a reference ahead: \DEX[]{Carla}

\begin{greement}[label={abc:3-1}]{Maximum}
  An input whose output is larger than the outputs of nearby inputs
\end{greement}

\INDEX[pm]{$\pm$}
\newpage

A function can have more than one \DEX{minimum}.

A function can have more than one \DEX{minimum}.

\chapter{one} \textbf{Andy}\INDEX[]{Andy} \chapter{two} \textbf{Beth}\INDEX[]{Beth} \chapter{three} \textbf{Carla}\INDEX[]{Carla} \chapter`{four}` \DEX[]{Andy} \DEX[]{Beth} .


\clearpage
\hypersetup{%
  linkcolor=backwardlinkcolor
}
\printindex


\end{document}