X-Git-Url: https://git.donarmstrong.com/?a=blobdiff_plain;f=mf%2FREADME;h=adf02251458d7da4fc5a1de0a8a63c14a2cc4bae;hb=039992242fc9a9c004329b786c08f66e6a0600e1;hp=8f78c89183e523b500196a05107e538c8fe8a906;hpb=95de6911a5cd1f90dfcd72ec798f089f6522f50f;p=lilypond.git diff --git a/mf/README b/mf/README index 8f78c89183..adf0225145 100644 --- a/mf/README +++ b/mf/README @@ -1,5 +1,125 @@ -This is a font of music symbols. All MF sources are original. Most -of the doco is in comments in the MF code, and in -Documentation/tex/fonts.doc +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 + +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 ., where is defined + with the `fet_begingroup' command, and 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 + 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-noteheads.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.