[why]
Some glyphs are just used as overlays for 'real' glyphs. These can be
for example U+0300 .. U+036F (the 'COMBINING ...' diactritics) like
U+0300, gravecomb, COMBINING GRAVE ACCENT
U+0301, acutecomb, COMBINING ACUTE ACCENT
U+0308, uni0308, COMBINING DIAERESIS
They are never used on their own, at least they are overlayed over a
blanc (U+0020, space).
For the font rendering engine they need to have the correct negative
bearings, so they are shifted to take no space by themselves.
The font-patcher script does not allow negative bearings in monospaced
fonts. This makes sense if every glyph is in itself a 'letter' that
should not reach beyond it's allotted (monospaced) space.
[how]
In the font-patcher script we do not touch the bearings of such overlay
glyphs. They can be identified by their width of zero.
For Windows to detect this font as 'monospaced' we need to change the
width to the standard width, though.
Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>
[why]
For some reason reading a font into fontforge looses data on glyphs. As
a workaround the `font-patcher` script has the switch `--mono` to
ascertain an equal width of all glyphs. We want to (and sometimes need to)
use that mode of the script to get a new font that is detected as monospaced
by Windows.
Sometimes that workaround fails. For example it breaks ligature glyphs
in some circumstances; they seem to be moved sideways.
[how]
The workaround is done in two steps: First each glyph is checked for
negative bearings. If these are found they are set to fixed zero.
Afterwards the glyph width is set to the font global width.
The ligature glyphs have already the correct width, they just have
negative bearings that they indeed need. There is no reason to change
the (correct) bearings to get a monospaced font. In strict monospaced
fonts that would be impossible, but the ligatures are only used in
applications that could work with negative bearings and so they should
be there. Strict monospaced usage does ignore the bearings anyhow.
Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>
