Perfect alignment, LuaTex and sidebearings. Part II

Question

I want to achieve a perfect alignment of the right (and/or left) margins of all the lines of paragraph (to the ink), among the lines themselves and eventually with other geometric elements of a page.

It can be done in xetex provided that you know the text in advance, and then to use the information provided by the bounding box of the last (or the first) glyph to offset the gap, using the proper sidebearing. Precision copyfitting in xcoffin

But the solution is unsuitable with unknown material that might appear in templates or to implement in chapter’s styles, where you need to let the TeX linebreaking finish its job before being able to see the final layout.

A general approach is to use the post_linebreak_filter in LuaTex. It was provided by Marcel Krüger in sidebearings and precision left/right alignment

“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.”

Unfortunately Marcel's solution used xadvance, an undocumented "field", which was dropped in Luatex 1.08.0.

I must say that the effect (or defect) it is only noticeable in long lines with large fonts, or when you want to align text with geometric elements present in the page. See the MWE that follows.

You should notice that even in “normal”, justified text, the uneven gap is not suppressed.

Is there an alternative solution?

% !TeX TS-program = lualatex

%%% IT DOES NOT WORK WITH LUATEX 1.08 or LATER !!!
%%% IT FAILS WITH LUATEX 1.08 or LATER !!!
%%% >>  warning (node filter): error: [\directlua]:11: attempt to perform 
%%%     arithmetic on field 'xadvance' (a nil value) 

\documentclass[12pt]{article}    
\RequirePackage{xcolor}
\RequirePackage{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 6\baselineskip depth 5pt width 0.1pt}%
  \kern-0.1pt
}

\begin{document}  
\pagestyle{empty}  

\newcommand{\longtitles}{Long titles must be exactly aligned with the vertical green bar.}% the main title

Note the {\bfseries uneven} gap between the text and the green line.
\vspace{3\baselineskip}

\begin{minipage}{5in}
    \dropsidebearings=0  %correction OFF    
    \raggedleft\sffamily\fontsize{60}{72}\selectfont\bfseries \longtitles\hairlineiv
\end{minipage}

\newpage

Perfect aligment! Each whole line was right shifted by a different amount.
\vspace{3\baselineskip}

\begin{minipage}{5in}
  \dropsidebearings=1  %correction ON     
 \raggedleft\sffamily\fontsize{60}{72}\selectfont\bfseries \longtitles\hairlineiv
\end{minipage}

\end{document} 

Answer 1

You can just insert kerns instead of using the xadvance and xoffset fields.

\documentclass[12pt]{article}    
\RequirePackage{xcolor}
\RequirePackage{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 kern = node.new(node.id'kern')
                kern.kern = - f.shared.rawdata.descriptions[char.char].boundingbox[1]*f.size/1000
                n.head = node.insert_before(n.head, char, kern)
            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]
                local kern = node.new(node.id'kern')
                kern.kern = - (desc.width-desc.boundingbox[3])*f.size/1000
                node.insert_after(n.head, char, kern)
            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 6\baselineskip depth 5pt width 0.1pt}%
  \kern-0.1pt
}

\newcommand{\hairlinevi}[1][green]{% 
  \leavevmode%
  \kern-0.1pt %
  \smash{\color{#1}\vrule depth 6\baselineskip height 2ex width 0.1pt}%
  \kern-0.1pt
}
\begin{document}  
\pagestyle{empty}  

\newcommand{\longtitles}{Long titles must be exactly aligned with the vertical green bar.}% the main title

Note the {\bfseries uneven} gap between the text and the green line.
\vspace{3\baselineskip}

\begin{minipage}{5in}
    \dropsidebearings=0  %correction OFF    
    \raggedleft\sffamily\fontsize{60}{72}\selectfont\bfseries \longtitles\hairlineiv
\end{minipage}

\newpage

Perfect aligment! Each whole line was right shifted by a different amount.
\vspace{3\baselineskip}

\begin{minipage}{5in}
  \dropsidebearings=1  %correction ON     
 \raggedleft\sffamily\fontsize{60}{72}\selectfont\bfseries \longtitles\hairlineiv
\end{minipage}

\begin{minipage}{5in}
  \dropsidebearings=1  %correction ON     
 \raggedright\sffamily\fontsize{60}{72}\selectfont\bfseries \hairlinevi\longtitles
\end{minipage}

\end{document}

Answer 2

You can achieve the effect you are after by setting suitable protrusion values. The values can be adjusted quite finely by font and font family (the example doesn't try this). It is probably possible to create the values with some lua code. (I moved the hairline, so that it doesn't disturb the protrusion of the period)

\documentclass[12pt]{article}
\RequirePackage{xcolor}
\RequirePackage{microtype}
\SetProtrusion
{encoding= *}
{l = { ,178},
 h = { ,120},
 . = { ,270}}

\newcommand{\hairlineiv}[1][green]{%
  \leavevmode%
  \kern-0.1pt %
  \smash{\color{#1}\vrule height 6\baselineskip depth 5pt width 0.1pt}%
  \kern-0.1pt
}

\begin{document}
\pagestyle{empty}

\newcommand{\longtitles}{Long titles must be exactly aligned with the vertical green bar.}% the main title

\begin{minipage}{5in}    
    \raggedleft\sffamily\fontsize{60}{72}\selectfont\bfseries \longtitles

    x\hairlineiv
\end{minipage}

\end{document}