-This is a font of music symbols. All MF sources are original. The
-symbols are modelled after various editions of music, notably
+LilyPond's Feta and Parmesan fonts
+==================================
- - Baerenreiter
- - Hofmeister
- - Breitkopf
- - Durand & C'ie
+[The name `feta' is based on a non-translatable Dutch pun (`font-en-tja').
+ Given that it is the name of a cheese type, the font for old music symbols
+ is called `parmesan', and the OpenType font that merges these two fonts is
+ called `emmentaler'.]
-The best references on Music engraving are [Wanske] and [Ross], some
-of their insights have also been used. Although a matter of taste,
-I'd say that Baerenreiter has the finest typography of all.
+This is a font of music symbols. All MetaFont sources are original. Most
+of the documentation is in comments in the MetaFont code.
-Traditional engraving uses a set of 9 standardised sizes for Staffs
-(running from 0 to 8).
+Non-square pixels are not supported; with other words, the horizontal and
+vertical resolution of the output device must be the same.
-I tried measuring those (helped by a magnifying glass), and I get the
-staffsizes in the following table. One should note that these are
-estimates, so I think there could be a measuring error of ~ .5 pt.
-Moreover [Ross] states that not all engravers use exactly those sizes.
-Staffsize Numbers Name
+Conversion from MetaFont to PostScript
+--------------------------------------
-26.2pt No. 0
-22.6pt No. 1 Giant/English
-21.3pt No. 2 Giant/English
-19.9pt No. 3 Regular, Ordinary, Common
-19.1pt No. 4 Peter
-17.1pt No. 5 Large middle
-15.9pt No. 6 Small middle
-13.7pt No. 7 Cadenza
-11.1pt No. 8 Pearl
+The MetaFont code gets directly converted to PostScript Type 1 font with a
+tool called `mf2pt1', which in turn calls `FontForge' to postprocess the
+output (mainly to remove outline overlaps and to add hints).
+The recommended calling sequence of mf2pt1 is
-This table is partially taken from [Ross]. Most music is set in No.3,
-but the papersizes usually are bigger than standard printer paper
-(such as A4). If you plot these, you'll notice that the sizes (With
-exception of 26) almost (but not quite) form a arithmetic progression.
+ mf2pt1 --rounding=0.0001 <other options> <font>
-[Ross] states that the dies (the stamps to make the symbols) come in
-12 different sizes.
+You need mf2pt1 version 2.1 or newer.
+Here some guidelines to assure a clean conversion.
+. Never use `---'. Replace it with `--' together with explicit path
+ directions (if necessary).
+
+. Don't use self-intersecting outlines in general since they can confuse
+ mf2pt1's algorithm to get the orientation of a closed path. Note that
+ MetaPost's implementation of the `turningnumber' primitive (which would
+ immediately give the orientation of a path) is severely broken before
+ version 1.0 of MetaPost, thus some hand-made code in mf2pt1.mp is used
+ to work around this bug.
+
+. If outlines intersect, avoid grazing intersections. In case two outlines
+ intersect in an explicitly defined point, include this point in both
+ intersecting paths to avoid problems due to rounding errors.
+
+. Don't use `draw' with a polygonal pen but for straight lines (consisting
+ of exactly two points). In most cases it is quite easy to emulate `draw'
+ with an explicit definition of the outline or with `penstroke'.
+
+. Don't apply transformations after calling `fill' -- for example, don't
+ mirror `currentpicture'. Instead, transform the path and call `fill'
+ afterwards. This ensures that mf2pt1 gets the correct outline directions,
+ which is a necessary prerequisite for FontForge's algorithm to remove
+ overlaps.
+
+
+Glyph name rules
+----------------
+
+. Most glyph names have the form <group>.<name>, where <group> is defined
+ with the `fet_begingroup' command, and <name> is given with
+ `fet_beginchar' (within a `fet_begingroup' block). Example:
+ `clefs.vaticana.fa'.
+
+. Sometimes it would be sensible to use negative numbers in glyph names.
+ However, the `-' character shouldn't be used in a glyph name. Replace it
+ with `M'. For example, write `rests.M3mensural' instead of
+ `rests.-3mensural'.
+
+. Glyphs that exist in both an `up' and `down' version should start the
+ <name> part with either `u' or `d', respectively. Example: `flags.d3',
+ `flags.u3'. Glyphs that are neutral w.r.t. the direction, and where
+ members of the glyph group exist that have `up' and `down' versions,
+ should start with an `s'. Example: `noteheads.s0re'.
+
+
+Design rules
+------------
+
+. Always use smooth curve transitions. Since this is difficult to see in
+ MetaFont proof sheets (which don't show the tangents) I recommend to call
+ mf2pt1 like this
+
+ FONTFORGE=foo mf2pt1 ...
+
+ (`foo' should be a non-existent program; this avoids the default
+ postprocessing). Then call FontForge to inspect the outlines.
+
+. Use rounded corners.
+
+
+Hints for stem attachment
+-------------------------
+
+. Stem attachment of glyphs is controlled by two special variables called
+ `charwx' and `charwy'. Stems can be regarded as (very oblonged)
+ rectangles with slightly rounded corners. For stems pointing upwards the
+ lower right corner of this rectangle is attached to the glyph at position
+ (charwx, charwy). For stems pointing downwards it works analogously but
+ with the upper left corner, where the position of the attachment point is
+ additionally reflected horizontally about the center of the glyph -- this
+ ensures that in most cases `charwx' and `charwy' can be set to the same
+ values for up and down stems even though these are attached at the
+ right/left end of the note, respectively. To make this more precise, the
+ upper left corner of a down stem is attached at position
+
+ (charwd/2 - charwx, charwy) ,
+
+ where `charwd' is an internal MetaFont variable representing the glyph
+ width as specified by the `set_char_box' command.
+
+. In case different stem attachments for upward and downward pointing stems
+ are needed, two separate glyphs must be defined in the MetaFont file; of
+ course, this also applies if two entirely different shapes are needed.
+ These have the same name but are prefixed by `u' and `d', respectively
+ (for `up' and `down', obviously). In each of these glyphs the variables
+ `charwx' and `charwy' must be set accordingly. If, on the other hand, the
+ attachment point is the `same' for both directions (with the
+ abovementioned horizontal reflection taken into account), then the prefix
+ `s' (for `symmetric') should be used. See the existing files for
+ examples. The numbers in the glyph names refer to the duration of the
+ note; e.g., `s0cross' in feta-noteheads.mf defines the notehead for a
+ whole cross-shaped note (similarly, `s1cross' and `s2cross' are for half
+ and quarter notes, respectively).
+
+
+Proofing
+--------
+
+The proofing tool for MetaFont to inspect its output is `gftodvi',
+converting a font in MetaFont's native GF font format to a DVI document,
+which can then be viewed with DVI viewers like `xdvi'. The `gftodvi'
+program needs two special fonts, `gray' and `black'. Assuming that you are
+using TeXLive, say
+
+ mktextfm gray
+ mktextfm black
+
+on the command line to generate the needed metric files (from its source
+files), which are then stored within your local TEXMF tree.
+
+Here is a shell script that you can use to produce two DVI files,
+`foo.proof.dvi' and `foo.ljfour.dvi', showing the glyphs of font `foo.mf' in
+proofing mode and a 600dpi rasterization for a LaserJet IV printer.
+
+ #!/bin/sh
+ mf "\mode:=proof; input $1"
+ gftodvi $1.2602gf && mv $1.dvi $1.proof.dvi
+
+ mf "\mode:=ljfour; input $1"
+ echo "grayfont black
+ " | gftodvi $1.600gf/ \
+ && mv $1.dvi $1.ljfour.dvi
+
+Assuming that you name this script `makefeta.sh', you can call it with e.g.
+
+ sh makefeta.sh feta23
+
+The main importance of the proofing DVI output is to show points marked in
+the MetaFont source code with the macros `penlabels' and `labels'. In most
+cases, those points are used for constructing the shapes only and are thus
+not present in the output after the conversion with mf2pt1.
+
+
+Rasterization
+-------------
+
+Finally, some rules to assure that rasterization at low resolutions
+(produced directly with MetaFont) gives good results. Today, this is a
+minor issue, but in some cases it might show design flaws.
+
+. Use `define_whole_pixels' and friends where appropriate.
+
+. Use `hround' and `vround' consistently. A lot of auxiliary macros are
+ defined in feta-macros.mf.
+
+. If a path element is duplicated or shifted, use an integer value for the
+ offset.
+
+. Add `eps' for mirrored paths to assure correct MetaFont rasterization.
+ See the comment and the variables at the end of `feta-params.mf' for
+ details how vertical symmetry should be achieved.
projects / lilypond.git / blobdiff