@Section
   @Title { Overhead transparencies }
   @Tag { overheads }
@Begin
@PP
To produce overhead transparencies
@FootNote {
In Version 3.15 overhead transparencies were updated and brought into line
with the other document types.  Although existing source files do not need
to be modified, their printed appearance may change (spacing, running
headers).  There are some new setup file options, and some changes to
existing setup file options.
}
(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.  A good font size for
overheads is 20 points, 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.
@Code "@InitialSpace" determines how Lout treats white space between
objects (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.  See preceding sections for {@Code "@OptimizePages"}.
@PP
After the compulsory {@Code "//"} come the overheads themselves.  There
are two alternatives:  a series of overheads, corresponding to a single
lecture, or a series of series of overheads, corresponding to a series
of lectures.  If the first is wanted, use this arrangement:
overhead. @Index @Code "@Overhead"
@ID @OneRow @Code {
"@SysInclude { slides }"
"@OverheadTransparencies"
"    @Title { ... }"
"    @Author { ... }"
"    @DateLine { ... }"
"    ..."
"//"
"@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
@Code "@Overhead" also has a @Code "@Format" option which allows you to
specify an arbitrary format for the body of the overhead (that is,
everything except its title).  For example,
@ID @Code "@Format { @CurveBox @HExpand @VExpand @Body }"
encloses the body in a curvebox, with the box expanded to the full
available width and height.  Unlike the similar option for figures
and tables, however, this @Code "@Format" option unfortunately has
not been set up to work with multi-page overheads, so if you use the
format just given you have to make sure your overheads all fit on one
page.  To draw boxes around the @I entire page, use the @Code "@PageBox"
setup file options.
@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 a series
of lectures, like this:
lecture. @Index @Code "@Lecture"
@ID @OneRow @Code {
"@SysInclude { slides }"
"@OverheadTransparencies"
"    @Title { ... }"
"    @Author { ... }"
"    @DateLine { ... }"
"    ..."
"//"
"@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.  Any text following the @Code "@Begin"
will appear under the lecture title as you would expect.  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"
"..."
"@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.  The setup file
options have been set on the assumption that you want your lectures
to appear in the table of contents, but not individual overheads.  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 "@OverheadSetup"
symbol whose options control the appearance of features specific to
overhead.setup. @Index @Code "@OverheadSetup"
overheads (in other words, the features described in this section).  Here
are some of these options and their default values:
@ID @OneRow @Code {
"@Use { @OverheadSetup"
"  # @DateLine { No }"
"  # @FirstOverheadNumber { 1 }"
"  # @FirstLectureNumber { 1 }"
"  # @ContentsWord { contents }"
"  # @LectureNumbers { Arabic }"
"  # @OverheadNumbers { Arabic }"
"  # @TitlePageFont { Helvetica Base }"
"  # @LectureHeadingFont { Bold 1.20f }"
"  # @LectureHeadingFormat { @Centre number @DP @Centre title @DP }"
"  # @OverheadHeadingFormat { @Centre title @DP }"
"  # @OverheadHeadingFont { Bold }"
"  # @LectureInContents { Yes }"
"  # @OverheadInContents { No }"
"  # @ReferencesInContents { Yes }"
"}"
}
For an introduction to setup files and their options, consult
Section {@NumberOf setup}.  The first four options are as for
@Code "@OverheadTransparencies" as described above.  @Code "@ContentsWord"
determines the 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 setting the font of the overall title page, the
title page of each lecture, and so on, and finally options which
determine which entries are made in any table of contents.
@PP
The @Code "@LectureHeadingFormat" option determines the
format of the heading of each lecture.  Within it, the symbol @Code "number" 
stands for the number of the lecture, including the `Lecture' word if
there is one, and @Code "title" stands for the title of the lecture.  The
default value centres the number and title, with display gaps below
each one.  @Code "@OverheadHeadingFormat" is similar; it has the same
symbols but the default value chooses not to use {@Code "number"}.
@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