@Section
   @Title { Precise object placement }
   @Tag { precise }
@Begin
@PP
This section offers some tips on placing objects precisely where you want
them relative to each other.  If your problem is to place objects precisely
at some unusual point on the page, you probably need a margin note or the
@Code "@Place" symbol, for which see Section {@NumberOf marginnotes}.
@PP
Precise object placement is not a subject with clear boundaries, so
this section is mainly a list of examples, covering the
@Code {"@OneCol"}, @Code {"@OneRow"}, @Code {"@Wide"}, @Code {"@High"},
@Code {"@HExpand"}, @Code {"@VExpand"}, @Code {"@HShift"}, @Code {"@VShift"},
@Code {"@VStrut"}, @Code {"@OverStrike"}, @Code {"@ZeroHeight"},
and @Code {"@ZeroWidth"} symbols.
@PP
The @Code "@OneCol" symbol causes the following object to be kept
onecol. @Index @Code "@OneCol"
on one line.  (The name stands for `one column', which is a bit
confusing unless you are an expert.)  For example, you could use
it to prevent hyphenation in a particular word, or to keep someone's
name together on one line:
@ID @Code "@OneCol { Mr. Jones }"
although there is also the @Code "~" symbol for that.  Similarly,
@Code "@OneRow" causes the following object to be kept in one
onerow. @Index @Code "@OneRow"
column.  It is commonly used to keep displays and list items
together:
@ID @Code "@IndentedDisplay @OneRow ..."
and 
@ID @Code "@ListItem @OneRow ..."
are the usual uses.
@PP
Loosely speaking, the @Code {"@Wide"} symbol causes the object following
wide. @Index @Code "@Wide"
it to have a particular width.  It also has a @Code "@OneCol" effect.
Paragraphs within the object will be broken if necessary in order to
satisfy the width restriction.  More precisely, the result of the
@Code {"@Wide"} symbol is an object with the given width, with the
following object fitting inside it, so having at most that width.  Compare
@ID @Code "5c @Wide @Box { A box }"
which produces
@ID 5c @Wide @Box { A box }
with
@ID @Code "@Box 5c @Wide { A box }"
which produces
@ID @Box 5c @Wide { A box }
In the first example, the only obligation on the box is to be
at most five centimetres wide, so that it fits into the space
allowed it.  In the second example, the box is drawn around
an object guaranteed to be exactly five centimetres wide.
The width of the box itself will be five centimetres plus twice the
box margin width.  Any length (Section {@NumberOf objects}) is allowed,
and the object following @Code "@Wide" may be arbitrary as usual.
@PP
The @Code "@High" symbol is like @Code {"@Wide"}, only vertical.  The two
high. @Index @Code "@High"
may be used together:
@ID @Code "@Box 5c @Wide 5c @High { A box }"
produces
@ID @Box 5c @Wide 5c @High { A box }
Be careful when using @Code "@High" to allow enough space for
whatever is inside.  An error message will be printed if you
don't, and the @Code "@High" symbol will be ignored.
@PP
Instead of a particular width, it is quite common to want something
to be as wide as possible.  For this there is the @Code "@HExpand"
hexpand. @Index @Code "@HExpand"
symbol:
@ID @Code "@IndentedDisplay @Box @HExpand { A box }"
produces
@IndentedDisplay @Box @HExpand { A box }
Notice how @Code "@HExpand" is placed after the @Code "@Box" symbol,
to ensure that the box is drawn around something as wide as possible,
analogously to the second @Code "@Wide" example above.  Lout has
carefully worked out that `as wide as possible' means the column width
minus the indent width and box margins.
@PP
Here is an example of @Code "@Wide" and @Code "@HExpand" working
together:
@ID @Box margin { 0.3c } 8c @Wide {
Name: @Underline @HExpand
@LP
Address: @Underline @HExpand
}
The problem is to get the underlines to be as wide as possible.
The solution is
@ID @Code @Verbatim {
@Box margin { 0.3c } 8c @Wide {
Name: @Underline @HExpand
@LP
Address: @Underline @HExpand
}
}
Each @Code "@HExpand" symbol produces for its result an object
which is as wide as possible, in this example containing nothing.
When that object is underlined, the underline is as wide as possible.
@PP
Although there is a corresponding @Code "@VExpand" symbol, it is not very
vexpand. @Index @Code "@VExpand"
useful alone because `as high as possible' does not mean `down to the foot
of the page' as you would expect.  It is mainly useful within
{@Code "@High"}.
@PP
The @Code {"@HShift"} and @Code {"@VShift"} symbols control the alignment
hshift. @Index @Code "@HShift"
vshift. @Index @Code "@VShift"
of objects with neighbouring objects.  There are not many places in document
formatting where alignment actually matters.  Ordinary lines of text are
one of them:
@ID @Code "faults such as {-0.3f @VShift s}lipped letters"
produces
@ID { faults such as {-0.3f @VShift s}lipped letters }
with the object following @Code "@VShift" aligned with neighbouring
objects such that it appears 0.3 times the current font size lower
than it normally would.  The object following @Code {"@VShift"} may
be arbitrary as usual.  Examples requiring @Code "@HShift" are very
rare; one appears below.
@PP
The @Code "@VStrut" symbol is used to compensate for missing
vstrut. @Index @Code "@VStrut"
letter ascenders and descenders.  For example, the three
boxes @Box { e }, @Box { f }, and @Box { g } look ragged
because their contents differ in their ascenders and descenders.
The solution is to insert a @I strut into each box:  an invisible
object of zero width whose height is that of a letter with both
an ascender and a descender.  This is done with the
@Code "@VStrut" symbol, which attaches such a strut to the
following object:
@ID @Code "@Box { @VStrut e }, @Box { @VStrut f }, and @Box { @VStrut g }"
produces
@ID { @Box { @VStrut e }, @Box { @VStrut f }, and @Box { @VStrut g } }
The @Code "@VStrut" symbol has @Code "above" and @Code "below" options
which determine how high and low (relative to the middle of the letter
`x') the strut is to go.  Their default values are both @Code { "0.5f" }.
@PP
Missing descenders can cause list items to appear unequally spaced,
because the space between list items is ordinarily measured from
the bottom edge of the higher list item to the top edge of the lower
one, rather than from baseline to baseline.  Enclosing the last word
of the troublesome items in @Code "@VStrut" will fix this problem.
@PP
Alternatively, and possibly more conveniently, Version 3.33 of Lout
has added a @Code "strut" option to the @Code "@Font" symbol, used
alone like this:
@ID @Code "strut @Font ..."
or in combination with other values suited to go to the left of
{@Code "@Font"}, like this:
@ID @Code "{ strut +2p } @Font ..."
This causes a vertical strut to be added to every word under the
influence of the {@Code "@Font"} symbol.  The height of this
kind of strut is fixed at the height of the highest character in
the font, and its depth at the depth of the deepest character,
as recorded by the `font bounding box' stored with the description
of the font.  For example,
@ID @Code "strut @Font { @Box { e }, @Box { @f }, and @Box { g } }"
produces
@ID strut @Font { @Box { e }, @Box { f }, and @Box { g } }
If you need many struts, it might pay to include @Code "strut"
in the @Code "@InitialFont" option of your document, so that it
applies everywhere.
@PP
The @Code "@OverStrike" symbol causes the objects on
overstrike. @Index @Code "@OverStrike"
each side of it to be overstruck:
@ID @Code "= @OverStrike \"/\""
produces
@ID { = @OverStrike "/" }
The objects to be overstruck may be arbitrary as usual.  For example,
Section {@NumberOf overall} recommends this symbol for overstriking
two graphs, to get what appears to be one graph with two coordinate
systems superimposed.  The second object is printed after the first
and will paint over it.
@PP
Sometimes the best way to get Lout to do what you want is to make it
pretend that some object has zero width or height, using the
zerowidth. @Index @Code "@ZeroWidth"
zeroheight. @Index @Code "@ZeroHeight"
@Code "@ZeroWidth" and @Code "@ZeroHeight" symbols.  Lout will
format the overall document as though the object in question had
zero width or height, but it will still print the entire object.
@PP
For example, you might have an inline equation that causes the
line spacing to increase to accommodate it -- @M { 2 sup 2 sup N } say --
but you would rather it didn't.  Writing
@ID @Code "@ZeroHeight @M { 2 sup 2 sup N }"
causes Lout to pretend that the object has zero height, and so
it will not increase the line spacing around this version of
{@ZeroHeight @M { 2 sup 2 sup N }}, as you can see.
@PP
The @Code "@HShift" and @Code "@VShift" symbols provide a way to move
the printed object with respect to the zero-width one:
@ID @Code @Verbatim {
{@ZeroWidth 1w @HShift ``}My dear Sir Thomas!'' cried
Mrs. Norris, red with anger, ``Fanny can walk.''
}
This example produces `hanging punctuation':
@ID 5c @Wide ragged @Break {
{@ZeroWidth 1w @HShift ``}My dear Sir Thomas!'' cried
Mrs. Norris, red with anger, ``Fanny can walk.''
}
The double quotes are printed at zero width, and @Code "1w @HShift"
ensures that they appear just to the left of the empty object that
Lout thinks it is placing, so that they protrude into the margin
rather than overstriking the next word (the Expert's Guide
@Cite { $kingston1995lout.expert } explains the @Code "w" unit of
measurement).
@PP
Some of the symbols described in this section are Lout primitives, described
in full detail in the Expert's Guide @Cite { $kingston1995lout.expert };
and that is also the place to look for more information about precise
object placement.  In particular, the Lout primitives described there
for horizontal and vertical concatenation, @Code "/" and {@Code "|"},
offer possibilities beyond what has been described here.
@End @Section