A LuaTeX solution. Should work in all situations that I am aware of:
\documentclass{article}
\usepackage{luacode,luatexbase}
\begin{document}
\begin{luacode*}
local GLYPH_ID = node.id("glyph")
local number_sp_in_a_pdf_point = 65782
function math.round(num)
return math.floor(num * 1000 + 0.5) / 1000
end
-- width/height/depth of a glyph and the whatsit node
local wd,ht,dp,w
-- head is a linked list (next/prev entries pointing to the next node)
function showcharbox(head)
while head do
if head.id == 0 or head.id == 1 then
-- a hbox/vbox
showcharbox(head.list)
elseif head.id == GLYPH_ID then
-- Create a pdf_literal node to draw a box with the dimensions
-- of the glyph
w = node.new("whatsit","pdf_literal")
wd = math.round(head.width / number_sp_in_a_pdf_point)
ht = math.round(head.height / number_sp_in_a_pdf_point)
dp = math.round(head.depth / number_sp_in_a_pdf_point)
-- draw a dashed line if depth not zero
if dp ~= 0 then
w.data = string.format("q 0.2 G 0.1 w 0 %g %g %g re S f [0.2] 0 d 0 0 m %g 0 l S Q",-dp,-wd,dp + ht,-wd)
else
w.data = string.format("q 0.2 G 0.1 w 0 %g %g %g re S f Q",-dp,-wd,dp + ht,-wd)
end
-- insert this new node after the current glyph and move pointer (head) to
-- the new whatsit node
w.next = head.next
w.prev = head
head.next = w
head = w
end
head = head.next
end
return true
end
luatexbase.add_to_callback("post_linebreak_filter",showcharbox,"showcharbox")
\end{luacode*}
A \emph{wonderful} serenity has taken {\large possession} of my entire soul, like these
\textsl{sweet}
\textbf{mornings} of spring which I enjoy with my whole heart. I am alone, and feel the
charm of existence in this spot, \textbf{which} was created for the bliss of souls like
mine. I am so happy, my dear friend, so absorbed in the exquisite sense of
mere tranquil existence, that I neglect my talents. I should be incapable of
drawing a single stroke at the present moment; and yet I feel that I never was
a greater artist than now.
\end{document}
which yields:
(detail)
Bonus: it draws the base line if the depth of the glyph is not 0.
Here is a solution that replaces the glyphs by black rectangles (rules):
\documentclass{article}
\usepackage{luacode,luatexbase,microtype}
\begin{document}
\begin{luacode*}
local GLYPH_ID = node.id("glyph")
-- head is a linked list (next/prev entries pointing to the next node)
-- parent it the surrounding h/vbox
function showcharbox(head,parent)
while head do
if head.id == 0 or head.id == 1 then
-- a hbox/vbox
showcharbox(head.list,head)
elseif head.id == GLYPH_ID then
r = node.new("rule")
r.width = head.width
r.height = head.height
r.depth = head.depth
-- replace the glyph by
-- the rule by changing the
-- pointers of the next/prev
-- entries of the rule node
if not head.prev then
-- first glyph in a list
parent.list = r
else
head.prev.next = r
end
if head.next then
head.next.prev = r
end
r.prev = head.prev
r.next = head.next
-- now the glyph points to
-- nowhere and we should remove
-- it from the memory
node.free(head)
head = r
end
head = head.next
end
return true
end
luatexbase.add_to_callback("post_linebreak_filter",showcharbox,"showcharbox")
\end{luacode*}
\hsize6cm
A wonderful serenity has taken possession of my entire soul, like these sweet
mornings of spring which I enjoy with my whole heart. I am alone, and feel the
charm of existence in this spot, which was created for the bliss of souls like
mine. I am so happy, my dear friend, so absorbed in the exquisite sense of
mere tranquil existence, that I neglect my talents. I should be incapable of
drawing a single stroke at the present moment; and yet I feel that I never was
a greater artist than now.
\end{document}
