[ui] Use fontconfig to find system fonts

I'm not sure I like fontconfig (docs are...), but it is pretty standard,
and I was able to find some reasonable examples on stackexchange
(https://stackoverflow.com/questions/10542832/how-to-use-fontconfig-to-get-font-list-c-c).
Currently, only the one font is handled, no font sets for fall backs
etc. It's meant for the debug UI I'm working on, so that shouldn't be a
big deal.

config.d/freetype.m4

@@ -30,3 +30,19 @@ AC_SUBST(HARFBUZZ_LIBS)
 if test "x$HAVE_HARFBUZZ" == "xyes"; then
 	AC_DEFINE(HAVE_HARFBUZZ, 1, [Define if you have the HarfBuzz library])
 fi
+
+AC_ARG_ENABLE(fontconfig,
+	AS_HELP_STRING([--disable-fontconfig], [disable fontconfig support]))
+if test "x$enable_fontconfig" != "xno"; then
+  if test "x$PKG_CONFIG" != "x"; then
+    PKG_CHECK_MODULES([FONTCONFIG], [fontconfig], HAVE_FONTCONFIG=yes, HAVE_FONTCONFIG=no)
+  fi
+else
+	HAVE_FONTCONFIG=no
+	FONTCONFIG_LIBS=
+fi
+AC_SUBST(FONTCONFIG_LIBS)
+
+if test "x$HAVE_FONTCONFIG" == "xyes"; then
+	AC_DEFINE(HAVE_FONTCONFIG, 1, [Define if you have the fontconfig library])
+fi

include/QF/ui/font.h

@@ -57,5 +57,7 @@ typedef struct font_s {
 void Font_Init (void);
 void Font_Free (font_t *font);
 font_t *Font_Load (QFile *font_file, int size);
+// free the returned string
+char *Font_SystemFont (const char *font_pattern);
 
 #endif//__QF_ui_font_h

libs/ui/Makemodule.am

@@ -8,6 +8,7 @@ gui_deps = \
 	libs/ui/libQFui.la
 
 gui_libadd = \
+	$(FONTCONFIG_LIBS) \
 	$(FREETYPE_LIBS) \
 	$(HARFBUZZ_LIBS)
 

libs/ui/font.c

@@ -32,6 +32,8 @@
 #endif
 #include <math.h>
 
+#include <fontconfig/fontconfig.h>
+
 #include "QF/quakefs.h"
 #include "QF/sys.h"
 #include "QF/math/bitop.h"
@@ -144,3 +146,25 @@ Font_Load (QFile *font_file, int size)
 
 	return font;
 }
+
+char *
+Font_SystemFont (const char *font_pattern)
+{
+	auto config = FcInitLoadConfigAndFonts ();
+	auto pattern = FcNameParse ((const FcChar8 *) font_pattern);
+	FcConfigSubstitute (config, pattern, FcMatchPattern);
+	FcDefaultSubstitute (pattern);
+
+	FcResult result;
+	auto font = FcFontMatch (config, pattern, &result);
+	char *filename = 0;
+	if (font) {
+		FcChar8 *str;
+		if (FcPatternGetString (font, FC_FILE, 0, &str) == FcResultMatch) {
+			filename = strdup ((char *) str);
+		}
+		FcPatternDestroy (font);
+	}
+	FcPatternDestroy (pattern);
+	return filename;
+}

libs/video/renderer/Makemodule.am

@@ -39,6 +39,7 @@ renderer_libs= \
 	libs/util/libQFutil.la
 
 renderer_libadd= \
+	$(FONTCONFIG_LIBS) \
 	$(FREETYPE_LIBS) \
 	$(HARFBUZZ_LIBS)