This is a font of music symbols.  All MF sources are original.  Most of the
documentation is in comments in the MF code.

Non-square pixels are not supported; with other words, the horizontal and
vertical resolution of the output device must be the same.

Currently, outline fonts are created by using `autotrace', but we are
already in the process of converting 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 recommended calling sequence of mf2pt1 is

  mf2pt1 --rounding=0.0001 <other options> <font>

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.


Some 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 which 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 which are neutral w.r.t. the direction, and where
  members of the glyph group exist which have `up' and `down' versions,
  should start with an `s'.  Example: `noteheads.s0re'.


Some 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-bolletjes.mf defines the notehead for a
  whole cross-shaped note (similarly, `s1cross' and `s2cross' are for half
  and quarter notes, respectively).


Finally, some rules to assure that rasterization at low resolutions 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.