custom header text and headrule

Question

Using mweclass LaTeX class (report based) is writing a document as follows:

\documentclass{mweclass}
\title{MWE}
\author{J. Doe}
\begin{document}
  \thispagestyle{mwetest}
  \maketitle
  \pagestyle{mwetest}
  \chapter{One}
  \section{First}
  % LaTeX code ...
\end{document}

In the header there must be a headrule on each page at a fixed offset in height.

But... when there are any g, q, p etc. letters in the text above (chapter or section names) the headrule is distanced correctly. Otherwise, the headrule is "attaching" to the text.

In a mweclass.cls I have this code for the mwetest pagestyle:

\newcommand{\ps@mwetest}{%
  \setlength\fancy@headwidth       {\mwe@textwidth}%
  \fancy@setoffs%
  \renewcommand\headrulewidth      {\mwe@headrulewidth}%
  \renewcommand\footrulewidth      {0pt}%
  \renewcommand\footruleskip       {0pt}%
  \def\headrule{\hrule\@height\headrulewidth\@width\headwidth\vskip-\headrulewidth}%
  \def\footrule{}%
  \def\f@ncyorh{\rightmark~\ \ \ \ \ ~\thepage}%
  \def\f@ncyelh{\thepage~\ \ \ \ \ ~\leftmark}%
  \def\@oddhead{\@fancyhead\fancy@Oolh\@empty\hfil\f@ncyorh\fancy@Oorh}%
  \def\@evenhead{\@fancyhead\fancy@Oelh\f@ncyelh\hfil\@empty\fancy@Oerh}%
  \def\@oddfoot{}\def\@evenfoot{}%
  \def\chaptermark##1{\markboth{##1\ -- \ \thechapter}{}}%
  \def\sectionmark##1{\markright{\thechapter.\arabic{section}\ --\ ##1}}%
}

Some code is taken from distributed fancyhdr.sty, version 3.2, lines 432-435. The \mwe@textwidth and \mwe@headrulewidth are calculated OK by the mweclass class before.

The problem is probably something to do with the baseline in letters. The headrule keeps attaching/detaching from the chapter / section names above, whether the text contains letters whose shape in the font prolongs below the baseline; or not.

1. Is there a way to insert invisible (that are not typeset) letters in a text? If there were, an easy workaround is to put a q in chapter and section names.
2. What is wrong? Except this mobile headrule, the header is but OK.

I appreciate any reply or suggestions.

Answer 1

You can put \strut command: it inserts a piece of nothing of the \height and \depth as large as the largest letters in current font, but having no \width.

Answer 2

Invisible characters are made with \phantom{txt}, \hphantom{txt} or \vphantom{txt}. The first takes width and height, the second width only and the third height only into account.