Add FcPatternFilter() (#13016)

doc/fcpattern.fncs

@@ -77,6 +77,18 @@ Returns whether <parameter>pa</parameter> and <parameter>pb</parameter> have exa
 objects in <parameter>os</parameter>.
 @@
 
+@RET@		FcPattern *
+@FUNC@		FcPatternFilter
+@TYPE1@		FcPattern * 			@ARG1@		 p
+@TYPE2@		const FcObjectSet * 		@ARG1@		 os
+@PURPOSE@	Filter the objects of pattern
+@DESC@
+Returns a new pattern that only has those objects from
+<parameter>p</parameter> that are in <parameter>os</parameter>.
+If <parameter>os</parameter> is NULL, a duplicate of
+<parameter>p</parameter> is returned.
+@@
+
 @RET@		FcChar32
 @FUNC@		FcPatternHash
 @TYPE1@		const FcPattern *		@ARG1@		p

fontconfig/fontconfig.h

@@ -740,6 +740,9 @@ FcPatternDuplicate (const FcPattern *p);
 FcPublic void
 FcPatternReference (FcPattern *p);
 
+FcPublic FcPattern *
+FcPatternFilter (FcPattern *p, const FcObjectSet *os);
+
 FcPublic void
 FcValueDestroy (FcValue v);
 

src/fcpat.c

@@ -997,6 +997,43 @@ FcPatternAppend (FcPattern *p, FcPattern *s)
     return FcTrue;
 }
 
+FcPattern *
+FcPatternFilter (FcPattern *p, const FcObjectSet *os)
+{
+    int		    i;
+    FcPattern	    *ret;
+    FcPatternElt    *e;
+    FcValueListPtr  v;
+
+    if (!os)
+	return FcPatternDuplicate (p);
+
+    ret = FcPatternCreate ();
+    if (!ret)
+	return NULL;
+
+    for (i = 0; i < os->nobject; i++)
+    {
+	FcObject object = FcObjectFromName (os->objects[i]);
+	e = FcPatternObjectFindElt (p, object);
+	if (e)
+	{
+	    for (v = FcPatternEltValues(e); v; v = FcValueListNext(v))
+	    {
+		if (!FcPatternObjectAddWithBinding (ret, e->object,
+						    FcValueCanonicalize(&v->value),
+						    v->binding, FcTrue))
+		    goto bail0;
+	    }
+	}
+    }
+    return p;
+
+bail0:
+    FcPatternDestroy (ret);
+    return NULL;
+}
+
 #define OBJECT_HASH_SIZE    31
 static struct objectBucket {
     struct objectBucket	*next;