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mkfn: add -O parameter to order otf lookups

In some languages like Arabic, some features should be applied first.
The -O argument of mkfn allows specifying the features to output
before any other feature.  For instance for Arabic, one should pass
"-O ccmp,rlig,calt,liga,dlig,cswh,mset" to mkfn.  Thanks to Behdad
Esfahbod <behdad@behdad.org> for the explanation.

--- a/README

+++ b/README

@@ -2,11 +2,16 @@

 ======

 The mktrfn program creates troff font description files for neatroff

-from AFM (Adobe Font Metrics) files.  TrueType and OpenType fonts can

-be first converted to AFM using programs like fontforge or

-lcdf-typetools (see ./gen.sh, for instance).  See the output of

-"mktrfn -h" for the available options.

+from AFM (Adobe Font Metrics) and TTF (TrueType Font) files.  OpenType

+fonts can be first converted to TTF (see ./gen.sh, for instance).  See

+the output of "mktrfn -h" for the available options.

 The included ./gen.sh script invokes mktrfn to create a complete

 output device for neatroff.  Change the variables in that file before

 running it.

+

+By default, font features are ordered as specified in the font.

+However, in some languages like Arabic, some features should be

+applied first.  The -O argument of mkfn allows specifying the features

+to output before any other feature.  For instance for Arabic, one

+should pass "-O ccmp,rlig,calt,liga,dlig,cswh,mset" to mkfn.

--- a/mkfn.c

+++ b/mkfn.c

@@ -17,6 +17,7 @@

 static char *trfn_scripts;	/* filtered scripts */

 static char *trfn_langs;	/* filtered languages */

+static char *trfn_featranks;	/* manual feature ordering */

 static char *afm_charfield(char *s, char *d)

 {

@@ -130,6 +131,12 @@

 	return !!strstr(trfn_langs, lang);

 }

+int trfn_featrank(char *feat)

+{

+	char *s = trfn_featranks ? strstr(trfn_featranks, feat) : NULL;

+	return s ? s - trfn_featranks : 1000;

+}

+

 int otf_read(void);

 void otf_feat(int res, int kmin, int warn);

@@ -146,6 +153,7 @@

 	"  -b      \tinclude glyph bounding boxes\n"

 	"  -S scrs \tcomma-separated list of scripts to include (help to list)\n"

 	"  -L langs\tcomma-separated list of languages to include (help to list)\n"

+	"  -O order\tfeatures to apply first (required only for some languages)\n"

 	"  -w      \twarn about unsupported font features\n";

 int main(int argc, char *argv[])

@@ -173,6 +181,9 @@

 			break;

 		case 'o':

 			afm = 0;

+			break;

+		case 'O':

+			trfn_featranks = argv[i][2] ? argv[i] + 2 : argv[++i];

 			break;

 		case 'p':

 			trfn_psfont(argv[i][2] ? argv[i] + 2 : argv[++i]);

--- a/otf.c

+++ b/otf.c

@@ -689,7 +689,11 @@

 static int lookupcmp(void *v1, void *v2)

 {

-	return ((struct otflookup *) v1)->lookup - ((struct otflookup *) v2)->lookup;

+	struct otflookup *l1 = v1;

+	struct otflookup *l2 = v2;

+	if (trfn_featrank(l1->feat) != trfn_featrank(l2->feat))

+		return trfn_featrank(l1->feat) - trfn_featrank(l2->feat);

+	return l1->lookup - l2->lookup;

 }

 /* extract lookup tables for all features of the given gsub/gpos table */

--- a/trfn.h

+++ b/trfn.h

@@ -7,3 +7,4 @@

 void trfn_kern(char *c1, char *c2, int x);

 int trfn_script(char *script, int nscripts);

 int trfn_lang(char *lang, int nlangs);

+int trfn_featrank(char *feat);