Issue 5806: Tweak mf files to avoid FontForge internal overlap error
When compiling LilyPond, there were 352 error messages caused by
FontForge trying to resolve overlapping path problems:
>>> Internal Error (overlap) in [...]
Fortunately, the resulting glyphs had been OK, though.
FontForge should be able to cope with this, but, alas, it isn't.
I've now tweaked all the mf files causing these problems so that the
annoying error messages can be avoided without while keeping the
original resulting glyph outlines.
modified: mf/feta-arrowheads.mf
- former def_set_arrow_paths (returning both open_path and close_path)
has been replaced by def_set_arrow_path returning one path arrow_path
depending on additional boolean parameter CLOSED
- No need to draw two overlapping mirrored half-paths anymore.
- Char definitions adapted accordingly
FIXES arrowheads.open.01
arrowheads.open.0M1
arrowheads.open.11
arrowheads.open.1M1
modified: mf/feta-braces.mf
- now draw one single cyclic path rather than overlaying two
separate, mirrored half-paths
- using intersection and subpaths to exaclty retain the original
slopes.
FIXES brace4 - brace507
modified: mf/feta-clefs.mf
- draw_gclef: just one control point changed (hidden in overlapping area)
FIXES clefs.G
clefs.GG
clefs.tenorG
- draw_tab_B: lower arc of the B in "TAB", angle slighty changed by 1°
FIXES clefs.tab
modified: mf/feta-numbers.mf
- original paths in char definition re-arranged, intersected, joined,
in order to create one single outline (two glyphs concerned):
- two char definitions affected:
FIXES two
FIXES seven
modified: mf/feta-scripts.mf
- draw_turn: "ploop" overlay completely removed, using joined sub-
paths instead
FIXES scripts.reverseturn
scripts.turn
scripts.slashturn
- "Segno" char definition: similar to draw_turn change
FIXES scripts.segno
modified: mf/feta-timesignatures.mf
- draw_C: .. instead of -- (hidden in overlapping area)
FIXES timesig.C44
timesig.C22
modified: mf/parmesan-clefs.mf
- draw_neomensural_c_clef: .. instead of -- (hidden in overlap area)
FIXES clefs.neomensural.c
clefs.neomensural.c_change
- draw_petrucci_c_clef: .. instead of .. (hidden in overlap area)
FIXES clefs.petrucci.c1
clefs.petrucci.c2
clefs.petrucci.c2_change
clefs.petrucci.c3
clefs.petrucci.c3_change
clefs.petrucci.c4
clefs.petrucci.c5
clefs.petrucci.c5_change
modified: mf/parmesan-rests.mf
- "2neomensural" char definition: one additional auxiliary point
inserted in overlap area
FIXES rests.2neomensural
>>> RESULT: same glyphs, no FontForge errors anymore
https://codereview.appspot.com/571780043
---
** [issues:#5806] Tweak mf files to avoid FontForge internal overlap error**
**Status:** Started
**Created:** Fri Feb 28, 2020 07:57 PM UTC by Torsten Hämmerle
**Last Updated:** Sat Feb 29, 2020 09:01 AM UTC
**Owner:** Torsten Hämmerle
**Attachments:**
-
[feta-braces-a.pfb](https://sourceforge.net/p/testlilyissues/issues/5806/attachment/feta-braces-a.pfb)
(24.8 kB; application/x-font-type1)
-
[internal-error-overlap-log.txt](https://sourceforge.net/p/testlilyissues/issues/5806/attachment/internal-error-overlap-log.txt)
(15.9 kB; text/plain)
#Overlapping mf paths
In some cases, overlapping mf paths will cause errors in FontForge processing,
even if the resulting glyphs seem to be OK.
Currently, we have **142 error messages** being produced during make, which is
quite annoying..
Please find the corresponding log extract attached.
**Remedy:** Slightly adapt mf code (where needed), keeping the resulting glyph
outline unchanged, but avoid problematic crossing angles for FontForge.
* slight path adaptions inside overlapping areas (not affecting the resulting
glyph outline at all!)
* In some cases (braces, arowheads, segno/turns) now using one single outline
rather than combinng two overlapping ones (with the exact same result).
##FontForge issue
This has been a pain in the neck for many years now, but it doesn't seem to be
easy to fix in FontForge, though. Werner has created a (FontForge) issue:
[https://github.com/fontforge/fontforge/issues/4184](https://github.com/fontforge/fontforge/issues/4184).
Nevertheless, it'd probably be a good idea to make our mf files a bit easier to
handle.
##Changes to mf files
The mf files have only been changed where needed, using all the original mf
control points and directions, keeping the *resulting* character outline
unaltered.
**I'll attach PFB files of feta11.pfb and feta.braces-a.pfb** so that Werner
(and others, of course) can have a look at the final FontForge output.
#### Overview: Internal Error (overlap) in [...]
The errors are being caused by just a few glyphs in just a couple of mf files.
Most of the time, there fixing one macro will fix all the glyphs using that
macro.
#####feta-arrowheads.mf -> Internal Error (overlap) in arrowheads.*
* macro **set_arrow_path**: now one single outline. Fixes glyphs **open.01,
open.0M1, open.11, open.1M1**
##### feta-scripts.mf -> Internal Error (overlap) in scripts.*
* macro **draw_turn**: "ploops" removed, now one single outline. Fixes glyphs
**reverseturn, turn, slashturn**
* char def **"segno"**: similar case as in draw_turn. Fixes glyph **segno**
##### feta-timesignatures.mf -> Internal Error (overlap) in timesig.*
* macro **draw_C**: smooth .. instead of straight -- within overlapping area.
Fixes glyphs **C44, C22**
##### feta-clefs.mf -> Internal Error (overlap) in clefs.*
* macro **draw_gclef**: Fixes glyphs **G, GG, tenorG**
* macro **draw_tab_B**: Starting angle of one stroke in lower handwriting
style "B" of "TAB" slightly changed (invisible difference). Fixes glyph **tab**
##### feta-braces.mf -> Internal Error (overlap) in brace*
* macro **draw_brace**: Even simplified a bit and now drawing one single
outline without any overlaps.
#### Examle: two overlaping outline -> single outline
In many symmetric cases, such as arrowheads braces, the glyphs had been
constructed by separately drawing half and a mirrored version of itself, thus
creating an overlap that *might* be problematic for FontForge.
**Original mf code (with overlap)**
~~~~
fill path;
fill path yscaled -1;
~~~~
**New mf code (one single outline)**
After determining the intersection point and using the appropriate subpath
only, we are able to draw one single cyclic outine by joining one half part and
its reversed/mirrored counterpart:
Using subpaths helps keeping the exact original control points and slopes, thus
keeping the resulting glyph exactly identical to the original glyph..
~~~~
fill path
.. reverse path yscaled -1
.. cycle;
~~~~
---
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