-This is a font of music symbols. All MF sources are original. Most
-of the documentation is in comments in the MF code.
+LilyPond's Feta and Parmesan fonts
+==================================
-Currently, outline fonts are created by using `autotrace', but we are
-already in the process to convert the MF code directly to PostScript code
-with a tool called `mf2pt1', which in turn calls `FontForge' to postprocess
-the output (mainly to remove outline overlaps and to add hints).
+[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'.]
+
+This is a font of music symbols. All MetaFont sources are original. Most
+of the documentation is in comments in the MetaFont code.
+
+Non-square pixels are not supported; with other words, the horizontal and
+vertical resolution of the output device must be the same.
+
+
+Conversion from MetaFont to PostScript
+--------------------------------------
+
+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
- mf2pt1 --rounding=0.001 <font>
+ mf2pt1 --rounding=0.0001 <other options> <font>
You need mf2pt1 version 2.1 or newer.
. Never use `---'. Replace it with `--' together with explicit path
directions (if necessary).
-. Don't use self-intersecting outlines in general since it can confuse
+. 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 and not
- fixed yet at the time of writing (November 2005), thus some hand-made code
- in mf2pt1.mp is used to work around this bug.
+ 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 into both
+ 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
. Don't apply transformations after calling `fill' -- for example, don't
mirror `currentpicture'. Instead, transform the path and call `fill'
- afterwards. This insures that mf2pt1 gets the correct outline directions
+ afterwards. This ensures that mf2pt1 gets the correct outline directions,
which is a necessary prerequisite for FontForge's algorithm to remove
overlaps.
-Some design rules:
+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
. Use rounded corners.
-Finally, some rules to assure that rasterization at low resolutions give
-good results. Today, this is a minor issue, but in some cases it might show
-design flaws.
+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.