font.eclass: introduce FONT_OPENTYPE_COMPAT for converting old bitmap fonts

>=x11-libs/pango-1.44 dropped support for old bitmap fonts. We can convert
(or really, wrap/embed) fonts from the legacy .bdf and .pcf formats into the OTB
wrapper format using x11-apps/fonttosfnt.

This commit adds FONT_OPENTYPE_COMPAT to font.eclass which packages installing
bitmap fonts can set to opt-in to conversion/wrapping.

Note that the font conversion isn't perfect -- it's good enough
in many cases, but in some cases they may require tweaking
via fontconfig to get pixel size right, antialiasing settings, ...

Adds IUSE=+opentype-compat to any ebuilds which set FONT_OPENTYPE_COMPAT;
enabled by default given discoverability of this issue may be difficult
and presumably any font package enabling FONT_OPENTYPE_COMPAT will be
useless without it anyway.

See also https://fedoraproject.org/wiki/BitmapFontConversion.

Bug: https://bugs.gentoo.org/698922
Thanks-to: Kerin Millar <kfm@plushkava.net>
Signed-off-by: Sam James <sam@gentoo.org>

eclass/font.eclass

@@ -46,6 +46,12 @@ FONTDIR=${FONTDIR:-/usr/share/fonts/${FONT_PN}}
 # Array containing fontconfig conf files to install.
 FONT_CONF=( "" )
 
+# @ECLASS_VARIABLE: FONT_OPENTYPE_COMPAT
+# @DEFAULT_UNSET
+# @DESCRIPTION:
+# Determines whether detected BDF and PCF font files should be converted
+# to an SFNT wrapper, for use with newer Pango.
+
 if [[ ${CATEGORY}/${PN} != media-fonts/encodings ]]; then
 	IUSE="X"
 	BDEPEND="X? (
@@ -54,6 +60,31 @@ if [[ ${CATEGORY}/${PN} != media-fonts/encodings ]]; then
 	)"
 fi
 
+if [[ -n ${FONT_OPENTYPE_COMPAT} ]] ; then
+	IUSE+=" +opentype-compat"
+	BDEPEND+=" opentype-compat? ( x11-apps/fonttosfnt )"
+fi
+
+# @FUNCTION: font_wrap_opentype_compat
+# @DESCRIPTION:
+# Converts .bdf and .pcf fonts detected within ${ED} to the OTB wrapper format
+# using x11-apps/fonttosfnt.  Handles optional .gz extension.
+font_wrap_opentype_compat() {
+	local file tmpfile
+
+	while IFS= read -rd '' file; do
+		if [[ ${file} == *.gz ]] ; then
+			tmpfile=${file%.*}
+
+			gzip -cd -- "${file}" > "${tmpfile}" \
+			&& fonttosfnt -v -o "${file%.*}.otb" -- "${tmpfile}" \
+			&& rm -- "${tmpfile}"
+		else
+			fonttosfnt -v -o "${file%.*}.otb" -- "${file}"
+		fi || ! break
+	done < <(find "${ED}" \( -name '*.bdf' -o -name '*.bdf.gz' -o -name '*.pcf' -o -name '*.pcf.gz' \) -type f ! -type l -print0) || die
+}
+
 # @FUNCTION: font_xfont_config
 # @DESCRIPTION:
 # Generate Xorg font files (mkfontscale/mkfontdir).
@@ -150,6 +181,10 @@ font_pkg_setup() {
 font_src_install() {
 	local dir suffix commondoc
 
+	if [[ -n ${FONT_OPENTYPE_COMPAT} ]] && in_iuse opentype-compat && use opentype-compat ; then
+		font_wrap_opentype_compat
+	fi
+
 	if [[ $(declare -p FONT_S 2>/dev/null) == "declare -a"* ]]; then
 		# recreate the directory structure if FONT_S is an array
 		for dir in "${FONT_S[@]}"; do