Fix issue 4355 -- broken beam subdivision

[lilypond.git] / Documentation / contributor / feta-font.itexi

diff --git a/Documentation/contributor/feta-font.itexi b/Documentation/contributor/feta-font.itexi
index 57a740bcc1867dc09fbac77b87173c7f69e3e2c3..002aa895a43167a4fc9eac319d2925e6de207b9e 100644 (file)
--- a/Documentation/contributor/feta-font.itexi
+++ b/Documentation/contributor/feta-font.itexi
@@ -5,7 +5,10 @@
 @menu
 * Overview of the feta font::
 * Font creation tools::
+* Adding a new font section::
+* Adding a new glyph::
 * Building the changed font::
+* METAFONT formatting rules::
 @end menu
 
 @node Overview of the feta font
@@ -15,7 +18,10 @@ The feta font is a font that was created specifically for use in
 LilyPond.  The sources for the font are found in mf/*.mf.
 
 The feta font is merged from a number of subfonts.  Each subfont
-can contain at most 223 glyphs.
+can contain at most 224 glyphs.  This is because each subfont is
+limited to a one-byte address space (256 glyphs maximum) and we
+avoid the first 32 points in that address space, since they are
+non-printing control characters in ASCII.
 
 In LilyPond, glyphs are accessed by glyph name, rather than by code point.
 Therefore, the naming of glyphs is significant.
@@ -36,7 +42,64 @@ available at CTAN.
 
 mf2pt1 is used to create type 1 fonts from the metafont sources.
 
-FontForge is used to display the resulting glyph shapes.
+FontForge is used to postprocess the output of mf2pt1 and clean up
+details of the font.  It can also be used by a developer to
+display the resulting glyph shapes.
+
+@node Adding a new font section
+@section Adding a new font section
+
+The font is divided into sections, each of which contains less
+than 224 glyphs.  If more than 224 glyphs are included in a section,
+an error will be generated.
+
+Each of the sections is contained in a separate @code{.mf} file.  The
+files are named according to the type of glyphs in that section.
+
+When adding a new section, it will be necessary to add the following:
+
+@itemize
+@item
+The code for the glyphs, in a file @code{<section-name>.mf}
+@item
+Driver files used to create the font in different sizes
+@item
+An entry in the generic file used to create the font, or a new
+generic file
+@item
+If necessary, new entries in the GNUmakefile
+@item
+An entry in @file{scripts/build/gen-emmentaler-scripts.py}
+@end itemize
+
+See the examples in @code{mf/} for more information.
+
+@node Adding a new glyph
+@section Adding a new glyph
+
+Adding a new glyph is done by modifying the .mf file to which the
+glyph will be added.
+
+Necessary functions to draw the glyph can be added anywhere in the file,
+but it is standard to put them immediately before the glyph definition.
+
+The glyph definition begins with:
+
+@example
+fet_beginchar ("glyph description", "glyphname");
+@end example
+
+@noindent
+with @code{glyph description} replaced with a short description of the
+glyph, and @code{glyphname} replaced with the glyphname, which is chosen
+to comply with the naming rules in @file{mf/README}.
+
+The metafont code used to draw the glyph follows the @code{fet_beginchar}
+entry.  The glyph is finished with:
+
+@example
+fet_endchar;
+@end example
 
 @node Building the changed font
 @section Building the changed font
@@ -50,3 +113,28 @@ rm mf/out/*
 make
 @end example
 
+@node METAFONT formatting rules
+@section METAFONT formatting rules
+
+There are special formatting rules for METAFONT files.
+
+Tabs are used for the indentation of commands.
+
+When a path contains more than two points, put each point on a
+separate line, with the operator at the beginning of the line.
+The operators are indented to the same depth as the initial point
+on the path using spaces.  The indentation mechanism is illustrated
+below, with @samp{------->} indicating a tab character and any other
+indentation created using spaces.
+
+@example
+def draw_something (test) =
+------->if test:
+------->------->fill z1
+------->------->     -- z2
+------->------->     -- z3
+------->------->     .. cycle;
+------->fi;
+enddef;
+@end example
+