@Section
   @Title { Overhead transparencies }
   @Tag { overheads }
@Begin
@PP
To produce overhead transparencies (hereafter called overheads), start off
overheads. @Index { overhead transparencies }
slides. @RawIndex { slides @I see overhead transparencies }
with the @Code slides setup file and the @Code "@OverheadTransparencies"
overhead.transparencies. @Index @Code "@OverheadTransparencies"
symbol:
@ID @OneRow @Code {
"@SysInclude { slides }"
"@OverheadTransparencies"
"    @Title {}"
"    @RunningTitle {}"
"    @Author {}"
"    @Institution {}"
"    @DateLine { No }"
"    @InitialFont { Times Base 20p }"
"    @InitialBreak { ragged 1.2fx nohyphen }"
"    @InitialSpace { lout }"
"    @InitialLanguage { English }"
"    @PageOrientation { Portrait }"
"    @PageHeaders { Titles }"
"    @FirstPageNumber { 1 }"
"    @FirstOverheadNumber { 1 }"
"    @FirstLectureNumber { 1 }"
"    @OptimizePages { No }"
"//"
}
This shows all the options of @Code "@OverheadTransparencies" with their
default values.  As usual with options, they may be given in any order, and
only the ones whose values need to be changed need be given at all.  The
meaning of the @Code "//" symbol after the last option is beyond our
scope, but disaster will ensue if it is forgotten.
@PP
If @Code "@Title" is not empty, an initial overhead will be produced
containing the {@Code "@Title"}, {@Code "@Author"}, {@Code "@Institution"},
and {@Code "@DateLine"} options.  @Code "@DateLine" may be set to
{@Code "No"}, meaning no dateline, {@Code "Yes"}, meaning print the current
date, or anything else, which is taken to be a date and printed.
@PP
Each overhead has a running header printed in small type at the top
left.  The @Code "@RunningTitle" option goes into this header, or, if
there is no @Code "@RunningTitle" option, @Code "@Title" is used instead.
@PP
The remaining options are a selection of setup file options (Section
{@NumberOf setup}) that frequently need to be changed.  If your changes
to the overall formatting are confined to these options, you can change
them here and avoid having your own setup file.  If you already have
your own setup file, change them in either place and omit them in
the other.
@PP
@Code "@InitialFont" is the font in which the overheads will be set, and
should contain a family, a face, and a size.  Experience shows that 20
points is a good font size for overheads, so that is the default size.
@PP
@Code "@InitialBreak" controls the behaviour of paragraph breaking in
the overheads.  It should have three parts:  a paragraph
breaking style ({@Code adjust}, {@Code ragged}, etc.), an inter-line
spacing ({@Code "1.2fx"} for single spacing, {@Code "2.4fx"} for
double spacing, and so on), and either @Code "hyphen" or @Code "nohyphen"
for turning hyphenation on or off.  Adjusted lines and hyphenated words
are difficult to read from overheads, so the default is not to have them.
@PP
@Code "@InitialSpace" determines how Lout treats white space between
two objects, as described in Section
{@NumberOf white}.  @Code "@InitialLanguage" determines the language
of the overheads.
@PP
@Code "@PageOrientation" determines the orientation of the page.  Its
value may be {@Code Portrait} (the default), {@Code Landscape},
{@Code ReversePortrait}, or {@Code ReverseLandscape}.  See
Section {@NumberOf pagesize} for further details.
@PP
@Code "@PageHeaders" determines the appearance of page headers and
footers.  Its value may be {@Code None}, {@Code Simple}, {@Code Titles},
or {@Code NoTitles}.  Section {@NumberOf headers} has the details, but
just briefly, {@Code None} produces no page headers, {@Code Simple} produces
page numbers only, @Code Titles produces full running titles, and
@Code "NoTitles" is similar to @Code "Simple" in this context.
@PP
@Code "@FirstPageNumber" is the number given to the first page,
@Code "@FirstOverheadNumber" is the number given to the first overhead,
and @Code "@FirstLectureNumber" is the number given to the first lecture,
of which more below.
@PP
Lout ordinarily places lines onto a page until space runs out, then moves
to the next page and so on.  This often produces ugly empty spaces at
the bottoms of pages preceding large unbreakable displays.  Setting the
@Code "@OptimizePages" option to {@Code "Yes"} causes Lout to examine the
overall situation and try to minimize the ugliness, using the @TeX
optimal paragraph breaking algorithm.  It takes two runs to do this,
with intermediate results stored in Lout's cross reference database
(Section {@NumberOf cross}); so deleting file {@Code lout.li} will reset
it, which might be wise after major changes.  It is possible for this
page layout optimizer to cycle, never settling on a single final best
version; this is usually caused by footnotes or floating figures inserted
at points which end up near page boundaries.
@PP
After the compulsory {@Code "//"} come the overheads themselves.  There
are two alternatives here:  you may either choose to make a simple
series of overheads, corresponding to a single lecture, or you may
choose to make a series of series of overheads, corresponding to a
series of lectures.  To make a simple series of overheads, use this
overhead. @Index @Code "@Overhead"
arrangement:
@ID @OneRow @Code {
"@SysInclude { slides }"
"@OverheadTransparencies"
"    ..."
"//"
"@Overhead ... @End @Overhead"
"@Overhead ... @End @Overhead"
"..."
"@Overhead ... @End @Overhead"
}
@Code "@Overhead" is a large-scale structure symbol, similar to
{@Code "@Section"}, with the usual options:
@ID @OneRow @Code {
"@Overhead"
"    @Title { Trends in investment since 1980 }"
"    @RunningTitle { Investment }"
"    @Tag { investment }"
"    @InitialLanguage { English }"
"@Begin"
"..."
"@End @Overhead"
}
If @Code "@Title" is given it will appear as a centred, bold display
at the beginning of the overhead.  As usual, these options may be given
in any order or omitted altogether.
@PP
The body of the overhead is quite arbitrary.  Typically one tends to
use lists and displays more than paragraphs, but all the usual features
are available.  Each overhead begins on a fresh page, but it may occupy
more than one page.
@PP
Lout does not provide any special support for overlays.  A good way to
make them is to first produce one overhead containing all the layers
simultaneously.  Once this is correct, enclose the entire body of the
overhead in {@Code "white @Colour"}, make one copy of the text of the
overhead for each layer, separating the copies with @Code "@NP"
(new page) symbols, and, in each copy, enclose the parts that are
to appear in that layer in {@Code "black @Colour"} (or any other
colour).  This works because @Code "white @Colour" makes an object
invisible without altering its size.
@PP
We turn now to the second major alternative, which is to make a series
of lectures, each of which is a series of overheads.  Use this arrangement:
lecture. @Index @Code "@Lecture"
@ID @OneRow @Code {
"@SysInclude { slides }"
"@OverheadTransparencies"
"    ..."
"//"
"@Lecture ... @End @Lecture"
"@Lecture ... @End @Lecture"
"..."
"@Lecture ... @End @Lecture"
}
@Code "@Lecture" is a large-scale structure symbol, again with
the usual options:
@ID @OneRow @Code {
"@Lecture"
"    @Title { Macro-Economic Policies for the Nineties }"
"    @RunningTitle { Macro-economic policies }"
"    @Tag { macro-economics }"
"    @InitialLanguage { English }"
"@Begin"
"..."
"@End @Lecture"
}
If @Code "@Title" is non-empty the series of overheads will begin with
an overhead containing the title alone, centred on the page using the
@Code "clines" paragraph breaking style.  This means that it makes
sense to have a multi-line title.
@PP
Within the body of {@Code "@Lecture"}, place a series of overheads
bracketed by @Code "@BeginOverheads" and {@Code "@EndOverheads"}:
beginoverheads. @Index @Code "@BeginOverheads"
endoverheads. @Index @Code "@EndOverheads"
@ID @OneRow @Code {
"@BeginOverheads"
"@Overhead ... @End @Overhead"
"@Overhead ... @End @Overhead"
"..."
"@Overhead ... @End @Overhead"
"@EndOverheads"
}
The @Code "@Overhead" symbol is exactly as described earlier.
@PP
The features described in other chapters are available with
overheads.  Endnotes and references appear automatically at the
end of the overheads.  You can have a table of contents, by setting
the @Code "@MakeContents" option of the setup file to {@Code Yes}.  It
will appear automatically after any title overhead.  However, it is not
possible to have an index, and it is not possible to have multiple columns.
@PP
Within the @Code slides setup file there is an @Code "@OverheadLayout"
symbol whose options control the appearance of features specific to
overhead.layout. @Index @Code "@OverheadLayout"
overheads (in other words, the features described in this section).  Here
are all these options and their default values:
@ID @OneRow @Code {
"@Use { @OverheadLayout"
"  # @DateLine { No }"
"  # @FirstOverheadNumber { 1 }"
"  # @FirstLectureNumber { 1 }"
"  # @ContentsWord { contents }"
"  # @LectureNumbers { Arabic }"
"  # @OverheadNumbers { Arabic }"
"  # @TitlePageFont { Helvetica Base }"
"  # @LectureHeadingFont { Bold 1.20f }"
"  # @OverheadHeadingFont { Bold }"
"  # @LectureInContents { Yes }"
"  # @OverheadInContents { No }"
"  # @ReferencesInContents { Yes }"
"}"
}
For general information about setup files and their options, consult
Section {@NumberOf setup}.  The first four options are as for
@Code "@OverheadTransparencies" as described above.  @Code "ContentsWord"
determines table of contents heading; its default value, {@Code contents},
produces `Contents' in the current language.  @Code "@LectureNumbers"
and @Code "@OverheadNumbers" determine the style of numbering of lectures
and overheads, and may be {@Code None}, {@Code Arabic}, {@Code Roman},
{@Code UCRoman}, {@Code Alpha}, or {@Code UCAlpha} as usual.  Next come
options for controlling the font used for the overall title page, the
title page of each lecture, and the heading of one overhead, and finally
three options which determine which entries are made in the table of
contents, if there is one.
@PP
Other setup file options exist which permit you to have a box drawn
around each overhead, and to change the page size, margins, and
orientation.  These are described in Chapter {@NumberOf changes}.
@PP
Section {@NumberOf headers} describes the setup file options that
control the appearance of page headers and footers.  With overheads,
the values given to the {@Code "@MajorTitle"}, {@Code "@MinorTitle"},
{@Code "@MajorNum"}, and {@Code "@MinorNum"} symbols within those
options are as follows.  If @Code "@Lecture" is being used:
@ID @Tab
    @Fmta { @Col A ! @Col B }
{
@Rowa
    A { @Code "@MajorTitle" }
    B { The @Code "@RunningTitle" option of
{@Code "@OverheadTransparencies"}, or its @Code "@Title" option
if @Code "@RunningTitle" is absent; }
@Rowa
    A { @Code "@MinorTitle" }
    B { The @Code "@RunningTitle" option of the current
{@Code "@Lecture"}, or else its @Code "@Title" option if
@Code "@RunningTitle" is absent; }
@Rowa
    A { @Code "@MajorNum" }
    B { The number of the current {@Code "@Lecture"}; }
@Rowa
    A { @Code "@MinorNum" }
    B { A two-part number, for example 5.2, containing the number of
the current @Code "@Lecture" and the number within that lecture
of the current overhead. }
}
If @Code "@Lecture" is not being used:
@ID @Tab
    @Fmta { @Col A ! @Col B }
{
@Rowa
    A { @Code "@MajorTitle" }
    B { The @Code "@RunningTitle" option of
{@Code "@OverheadTransparencies"}, or its @Code "@Title" option
if @Code "@RunningTitle" is absent; }
@Rowa
    A { @Code "@MinorTitle" }
    B { Empty; }
@Rowa
    A { @Code "@MajorNum" }
    B { Empty; }
@Rowa
    A { @Code "@MinorNum" }
    B { The number of the current overhead. }
}
The first page occupied by any overhead is a @Code Start page; subsequent
pages are @Code NonStart pages.  There are no @Code Intro pages.
@End @Section
