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** [issues:#5806] Tweak mf files to avoid FontForge internal overlap error**
**Status:** New
**Created:** Fri Feb 28, 2020 07:57 PM UTC by Torsten Hämmerle
**Last Updated:** Fri Feb 28, 2020 07:57 PM UTC
**Owner:** Torsten Hämmerle
**Attachments:**
-
[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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