sidebearings and precision left/right alignment

Question

As was suggested, I will rephrase my previous question, which is not confined in a coffin.

As @MartinScharrer rightly points out, I am asking how to optically align text at the margins after linebreaking, more specifically when you do not know in advance the content.

This is the case in templates, where the text is provided by a user.

Since TeX compose with boxes, the sidebearings are always there, but they become more noticeable when using large size fonts in title pages or posters.

Working with xelatex I solved this problem for single line sentences, but failed to do so with multiline paragraphs. (Again, text unknown in advance.)

Perfect alignment, single sentence, text unknown in advance.

Variable right gaps in a multiple line title.

The way I would like, (done by hand, known text)

    \documentclass{article}

    \RequirePackage{xcolor}
    \RequirePackage{xstring}

    %% scrapping sidebearing both L & R

    \newcommand\shaveLR[1]{% 
        \if\relax\detokenize{#1}\relax\else% check  empty
        \StrLeft{#1}{1}[\tempi]%    the first char
        \StrRight{#1}{1}[\tempii]%  the last char
        \kern-\XeTeXglyphbounds1 \the\XeTeXcharglyph\expandafter`\tempi% first char L un-kernig
        #1%  input string
        \kern-\XeTeXglyphbounds3 \the\XeTeXcharglyph\expandafter`\tempii% last char R un-kernig
        \fi}

        \newcommand{\hairlineiv}[1][green]{% 
        \leavevmode%
        \kern-0.1pt %
        \smash{\color{#1}\vrule height 4\baselineskip depth 5pt width 0.1pt}%
        \kern-0.1pt}

        \newcommand{\hairlinei}[1][red]{% 
        \leavevmode\kern-0.1pt %
        \smash{\color{#1}\vrule height 35pt depth 15pt width 0.1pt}%
        \kern-0.1pt}

    \newcommand{\byauthor}{}
    \newcommand{\longtitles}{}

    \begin{document}  
    \pagestyle{empty}   

    \renewcommand{\byauthor}{Your Name} % put your name here
    \renewcommand{\longtitles}{Long titles must be exactly align with the vertical green bar.}% the main title

    %%%% examples
    \newcommand{\thislongtitleR}{%
    \shaveLR{Long titles must be}\\%
    \shaveLR{exactly align with}\\%
    \shaveLR{the vertical green}\\%
    \shaveLR{bar.}}


    \Large \flushright
    Note the gap between\\ the red line and the 'e'.

    \vspace{\baselineskip}
    {\sffamily\fontsize{60}{60}\selectfont
     by \byauthor\hairlinei}
    \vspace{\baselineskip}

    No gap here after\\ zeroing the kern.

    \vspace{1\baselineskip}
    {\sffamily\fontsize{60}{60}\selectfont
        by \shaveLR{\byauthor}\hairlinei}
    \vspace{2\baselineskip}


    \newpage
    \Large \flushright The way it is:
    \vspace{1\baselineskip}
    \begin{minipage}{1.3\textwidth}
    \raggedleft\sffamily\fontsize{50}{60}\selectfont\bfseries \longtitles\hairlineiv\par
    \end{minipage}

    \vspace{2\baselineskip}
    \Large \flushright The way it should be:
    \vspace{1\baselineskip}

    \begin{minipage}{1.3\textwidth}
        \raggedleft\sffamily\fontsize{50}{60}\selectfont\bfseries \thislongtitleR\hairlineiv
    \end{minipage}

    \end{document}

Answer 1

A LuaTeX solution:

In LuaTeX, you can use the post_linebreak_filter to intercept the broken lines and add some offsets. The sidebearings can be extracted from rawdata saved by luaotfload. After adding the offsets, the hboxes have to be repacked to determine the new glue settings.

To apply this to every vertical box in your document, add in your preamble

\usepackage{luacode}
\begin{luacode*}
  local function drop_sidebearing(head, groupcode)
    for n in node.traverse_id(node.id'hlist', head) do
      local char = node.has_glyph(n.head)
      if char then
        local f = font.getfont(char.font)
        if f.shared then
          local off = f.shared.rawdata.descriptions[char.char].boundingbox[1]*f.size/1000
          char.xadvance = char.xadvance - off
          char.xoffset = char.xoffset - off
        end
      end
      for ch in node.traverse_id(node.id'glyph', n.head) do
        char = ch
      end
      if char then
        local f = font.getfont(char.font)
        if f.shared then
          local desc = f.shared.rawdata.descriptions[char.char]
          char.xadvance = char.xadvance - (desc.width-desc.boundingbox[3])*f.size/1000
        end
      end
      local new_list = node.hpack(n.head, n.width, 'exactly')
      new_list.head = nil
      n.glue_order = new_list.glue_order 
      n.glue_set = new_list.glue_set
      n.glue_sign = new_list.glue_sign 
      node.free(new_list)
    end
    return true
  end
  luatexbase.add_to_callback('post_linebreak_filter', drop_sidebearing, 'Drop sidebearings after linebreaking')
\end{luacode*}

EDIT: The same code integrated into the original example with an added parameter \dropsidebearings. The code will only have an effect if \dropsidebearings is not 0 at the end of the paragraph.

\documentclass{article}

\RequirePackage{xcolor}
\RequirePackage{xstring}

\usepackage{luacode}
\newcount\dropsidebearings
\begin{luacode*}
  local function drop_sidebearing(head, groupcode)
    if tex.count['dropsidebearings'] == 0 then
      return true
    end
    for n in node.traverse_id(node.id'hlist', head) do
      local char = node.has_glyph(n.head)
      if char then
        local f = font.getfont(char.font)
        if f.shared then
          local off = f.shared.rawdata.descriptions[char.char].boundingbox[1]*f.size/1000
          char.xadvance = char.xadvance - off
          char.xoffset = char.xoffset - off
        end
      end
      for ch in node.traverse_id(node.id'glyph', n.head) do
        char = ch
      end
      if char then
        local f = font.getfont(char.font)
        if f.shared then
          local desc = f.shared.rawdata.descriptions[char.char]
          char.xadvance = char.xadvance - (desc.width-desc.boundingbox[3])*f.size/1000
        end
      end
      local new_list = node.hpack(n.head, n.width, 'exactly')
      new_list.head = nil
      n.glue_order = new_list.glue_order 
      n.glue_set = new_list.glue_set
      n.glue_sign = new_list.glue_sign 
      node.free(new_list)
    end
    return true
  end
  luatexbase.add_to_callback('post_linebreak_filter', drop_sidebearing, 'Drop sidebearings after linebreaking')
\end{luacode*}

\newcommand{\hairlineiv}[1][green]{% 
  \leavevmode%
  \kern-0.1pt %
  \smash{\color{#1}\vrule height 4\baselineskip depth 5pt width 0.1pt}%
  \kern-0.1pt
}

\newcommand{\hairlinei}[1][red]{% 
  \leavevmode\kern-0.1pt %
  \smash{\color{#1}\vrule height 35pt depth 15pt width 0.1pt}%
  \kern-0.1pt
}

\begin{document}  
\pagestyle{empty}   

\newcommand{\byauthor}{Your Name} % put your name here
\newcommand{\longtitles}{Long titles must be exactly align with the vertical green bar.}% the main title

\Large \flushright
Note the gap between\\ the red line and the 'e'.
\protrudechars=1

\vspace{\baselineskip}
{\sffamily\fontsize{60}{60}\selectfont
 by \byauthor\hairlinei}
\vspace{\baselineskip}

No gap here after\\ zeroing the kern.

\vspace{1\baselineskip}
{\sffamily\fontsize{60}{60}\selectfont
    \dropsidebearings=1
    by \byauthor\hairlinei\par}
\vspace{2\baselineskip}


\newpage
\Large \flushright The way it is:
\vspace{1\baselineskip}
\begin{minipage}{1.3\textwidth}
  \raggedleft\sffamily\fontsize{50}{60}\selectfont\bfseries \longtitles\hairlineiv\par
\end{minipage}

\vspace{2\baselineskip}
\Large \flushright The way it should be:
\vspace{1\baselineskip}

\begin{minipage}{1.3\textwidth}
  \dropsidebearings=1
  \raggedleft\sffamily\fontsize{50}{60}\selectfont\bfseries \longtitles\hairlineiv
\end{minipage}

\end{document}