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=0.001 <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.


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.