* Documentation/user/lilypond-book.itely: small cleanups

[lilypond.git] / Documentation / user / introduction.itely

@c -*-texinfo-*-

@node Introduction
@chapter Introduction


LilyPond is a program to print sheet music. If you have used notation
programs before, then the way to use this program might be surprising
at first sight. To print music with lilypond, you have to enter
musical codes in a file. Then you run LilyPond on the file, and the
music is produced without any user intervention. For example,
something like this:

@lilypond[fragment,verbatim, relative 1, intertext="produces this"]
\key c \minor r8 c16 b c8 g as c16 b c8 d | g,4 
@end lilypond

@cindex encoding music

Encoding music using letters and digits may appear strange,
intimidating or even clumsy at first. Nevertheless, when you take the
effort to learn the codes and the program you will find that it is
easier than it seems.  Entering music can be done quickly, and you
never have to remember how you made the program do something
complicated: it's all in the input code, and you only have to read the
file to see how it works. Moreover, when you use LilyPond, you are
rewarded with very nicely looking output.

In this chapter, we will explain the reasoning behind this unusual
design, and how this approach affects you as a user.

@menu
* Batch processing::            
* Music engraving::             
* Music representation::        
* About this manual::           
@end menu

@node Batch processing
@section Batch processing

@cindex GUI
@cindex Batch
@cindex UNIX 

When we started developing LilyPond, we were still studying at the
university.  We were interested in music notation, not as publishers
or musicians, but as students and scientists. We wanted to figure to
what extent formatting sheet music could be automated.  Back then GUIs
were not as ubiquitous as they are today, and we were immersed in the
UNIX operating system, where it is very common to use compilers to
achieve computing tasks, so our computerized music engraving
experiment took on the form of a compiler.

@cindex free software
@cindex sharing software

You can freely use, modify and redistribute LilyPond. This choice was
also motivated by our academic background. In the scientific community
it has always been a tradition to share knowledge, also if that
knowledge was packaged as software. One of the most visible groups
that stimulated this philosophy, was the Free Software Foundation,
whose popular GNU project aimed to replace closed and proprietary
computing solutions with free (as in ``Libre'') variants. We jumped on
that bandwagon, and released LilyPond as free software.  That is the
reason that you can get LilyPond at no cost and without any strings
attached.


@node Music engraving
@section Music engraving



@cindex engraving
@cindex typography

Making sheet music may seem trivial at first (``you print 5 lines, and
then put in the notes at different heights''), @emph{music engraving},
i.e. professional music typography, is in another ballpark.  The term
`music engraving' derives from the traditional process of music
printing.  Only a few decades ago, sheet music was made by cutting and
stamping the music into zinc or pewter plates, mirrored. The plate
would be inked, and the depressions caused by the cutting and stamping
would hold ink.  A positive image was formed by pressing paper to the
plate. Stamping and cutting was completely done by hand. Making
corrections was cumbersome, so engraving had to be done correctly in
one go. As you can imagine this was a highly specialized skill, much
more so than the traditional process of printing books.

@cindex craftsmanship
@cindex master

The following fact illustrates that. In the traditional German
craftsmanship six years of full-time training, more than any other
craft, were required before a student could call himself a master of
the art. After that many more years of practical experience were
needed to become an established music engraver.  Even today, with the
use of high-speed computers and advanced software, music requires lots
of manual fine tuning before it acceptable to be published.

When we wanted to write a computer program to do create music
typography, we encountered the first problem: there were no sets of
musical symbols available: either they were not available freely, or
they didn't look well to our taste. Not let down, we decided to try
font design ourselves. We created a font of musical symbols, relying
on nice printouts of hand-engraved music.  It was a good decision to
design our own font. The experience helped develop a typographical
taste, and it made us appreciate subtle design details. Without that
experience, we would not have realized how ugly the fonts were that we
admired at first.


@lilypond
#(define magfact 3.0)
\score {  \notes { as'2 r4 }
          \paper {
              linewidth = -1. 
              \translator {
                  \ScoreContext
                  AccidentalPlacement \override #'right-padding = #3.0
                  StaffSymbol \override #'transparent =   ##t
                  Clef \override #'transparent = ##t
                  TimeSignature \override #'transparent = ##t             
                  Accidental \override #'font-magnification = #magfact
                  Rest \override #'font-magnification = #magfact
                  NoteHead \override #'font-magnification = #magfact
                  Stem \override #'transparent = ##t
                  } } }
@end lilypond

@cindex musical symbols
@cindex font
@cindex blackness
@cindex balance

The figure above shows a few notable glyphs. For example, the
half-notehead is not elliptic but slightly diamond shaped.  The
vertical stem of a flat symbol should be slightly brushed,
i.e. becoming wider at the top. Fine endings, such as the one on the
bottom of the quarter rest, should not end in sharp points, but rather
in rounded shapes.  Taken together, the blackness of the font must be
carefully tuned together with the thickness of lines, beams and slurs
to give a strong yet balanced overall impression.

Producing a strong and balanced look is the real challenge of music
engraving. It is a recurring theme with many variations.  In spacing,
the balance is in a distribution that reflects the character of the
music. The spacing should not lead to unnatural clusters of black and
big gaps with white space.  The distances between notes should reflect
the durations between notes, but adhering with mathematical precision
to the duration will lead to a poor result. Shown here is an example
of a motive, printed twice. It is printed using both exact,
mathematical spacing, and with some corrections. Can you spot which is
which?

@c I can only see the motive printed two times!!! /Mats

@cindex optical spacing
@lilypond
    \score { \notes {
      \property Staff.NoteSpacing \set #'stem-spacing-correction
        = #0.6
      c'4 e''4 e'4 b'4 |
       \stemDown b'4 e''4 a'4 e''4| \stemBoth
      \property Staff.NoteSpacing \override #'stem-spacing-correction
      = #0.0
      \property Staff.StaffSpacing \override #'stem-spacing-correction
      = #0.0
      c'4 e''4 e'4 b'4 |
      \stemDown b'4 e''4 a'4 e''4|      
    }
    \paper { linewidth = -1. } }
@end lilypond

@cindex regular rhythms
@cindex regular spacing

The fragment that was printed uses only quarter notes: notes that are
played in a constant rhythm. The spacing should reflect
that. Unfortunately, the eye deceives us a little: the eye not only
notices the distance between note heads, but also between consecutive
stems. The notes of a up-stem/down-stem combination should be put
farther apart, and the notes of a down-up combination should be put
closer together, all depending on the combined vertical positions of
the notes. The first two measures are printed with this correction,
the last two measures without. The notes in the last two measures form
downstem/upstems clumps of notes.

We hope that these examples show that music typography is a subtle
business, and that it requires skill and knowledge to produce good
engraving.  It was our challenge to see if we could put such knowledge
into a computer program.


@node Music representation
@section Music representation


One of the big questions when making programs, is what kind of input
the program should expect. Many music notation programs offer a
graphical interface that shows notation, and allow you to enter the
music by placing notes on a staff. Although this is a obvious way to
design a program, from our point of view, it is cheating. After all,
the core message of a piece of music notation simply is the music
itself. If you start by offering notation to the user, you have
already skipped one conversion, even if it is implicit. If we want to
generate music notation from something else, then the obvious
candidate for the source is the music itself.

On paper this theory sounds very good. In practice, it opens a can of
worms. What really @emph{is} music? Many philosophical treatises must
have been written on the subject. Even if you are more practically
inclined, you will notice that there exist an enormous number of ways
to represent music in a computer, and they are much more incompatible
than the formats for word processors and spreadsheets.  Anyone who has
tried to exchange data files from between different notation programs
can attest to this.

@cindex music representation
@cindex music expressions
@cindex input format

This problem is caused by the two-dimensional nature of music: in
polyphonic music, notes have time and pitch as their two coordinates,
and they often are related in both directions. Computer files on the
other hand are essentially one-dimensional: they are a long stream of
characters. When you represent music in a file, then you have to
flatten this two-dimensional information breaking either timing or
pitch relations, and there is no universal agreement on how to do
this.

Fortunately, we have a concrete application, so we don't run the risk
of loosing ourselves in philosophical arguments over the essence of
music.  We want to produce a printed score from a music
representation, so this gives us a nice guide for designing a format:
we need a format containing mainly musical elements, such as pitch and
duration, but also enough information to print a score.  Our users
have to key in the music into the file directly, so the input format
should have a friendly syntax. Finally, we as programmers and
scientists want a clean formal definition. After all, producing music
notation is a difficult problem, and in the scientific world, problems
can only be solved if they are well-specified. Moreover, formally
defined formats are easier to write programs for.

These ideas shaped our music representation: it is a compact format
that can easily be typed by hand. It complex musical constructs from
simple entities like notes and rests, in much the same way that one
builds complex formulas from simple expressions such as numbers and
mathematical operators.  The strict separation between musical
information and typesetting also gives a blueprint of the program:
first it reads the music representation, then it interprets the
music---reading it `left-to-right', and translating the musical
information to a layout specification. When the layout is computed,
the resulting symbols are written to an output file.


@node About this manual
@section About this manual


As you will notice in the coming pages the program makes good
decisions in a lot of cases: what comes out of LilyPond generally
looks good.  The default layout of lilypond even is suitable for
publication for some specific files. However, some aspects of the
formatting are not yet very good. For us programmers, this gives
inspiration for improving the program. However, most users are more
interested in improving their printouts, and then they have to make
manual adjustments to the output.  Another aspect of our system of
encoding through ASCII then shows: it can be complicated to fine tune
the layout of a piece. There is no graphical user interface, where you
can simply click and drag a symbol. On the other hand, if you have
written the code for tuning one specific aspect of the layout, then
you can simply store the file on disk, retrieve it when you need it:
there is no need to remember how you did it, since it is all in the
input file.

@cindex snippets
@cindex adjusting output

Lilypond also comes with a huge collection of snippets that show all
kinds of tricks.  This collection is much needed, because of the way
LilyPond is structured. It is a large program, but almost all of the
internal functionality is exported: that is, the variables that are
internally used for formatting the sheet music are available directly
to the user. These are variables to control thicknesses, distances,
and other formatting options. There are a huge number of them, and it
would be impossible to describe them all in a hand-written
manual. There is no need to despair, there is an `automatic' manual,
that lists all of the variables that are available.  It is directly
generated from the definitions that LilyPond itself uses, so it is
always up to date. If you are reading this from a screen: it is
available from the web, and is included with most binary
distributions.  If you're reading this from paper, then we advise you
to use the digital version anyway: the hyperlinks make finding topics
in the lilypond-internals manual much easier.

@cindex variables
@cindex properties
@cindex lilypond-internals
@cindex internal documentation 

For those who really want to get their hands dirty: it is even
possible to add your own functionality, by extending LilyPond in the
built-in scripting language, a dialect of the powerful programming
language Scheme. There is no real distinction between what a user can
do and what a programmer is allowed to do.

@cindex Scheme
@cindex extending lilypond

In summary, this manual does not pretend to be exhaustive, but it is
merely a guide that tries to explain the most important principles,
and shows popular input idioms.  The rest of the manual is structured
as follows: it starts with a tutorial that explains how to use
lilypond. In the tutorial, a number of fragments of increasing
complexity are shown and explained.  Then comes the reference manual,
which gives more detailed information on all features. If you're new
to lilypond, then you should start reading the tutorial, and
experiment for yourself.  If you already have some experience, then
you can simply use the manual as reference: there is an extensive
index.@footnote{If you are looking for something, and you can't find it
by using the index, that is considered a bug.  In that case, please
file a bug report}

@cindex bugreport
@cindex index
@cindex tutorial
@cindex overview of manual
@cindex idiom