Don't create hb_apply_context_t per glyph!

I couldn't measure significant performance gains out of this; maybe
about 5% (with one million Malayalam strings).  Still, not bad.
But reminds me that optimizing this codebase without profiling first
is simply not going to work.  Oh well...

src/hb-ot-layout-gpos-table.hh

@@ -1404,23 +1404,9 @@ struct PosLookup : Lookup
   inline const PosLookupSubTable& get_subtable (unsigned int i) const
   { return this+CastR<OffsetArrayOf<PosLookupSubTable> > (subTable)[i]; }
 
-  inline bool apply_once (hb_font_t *font,
+  inline bool apply_once (hb_apply_context_t *c) const
-			  hb_buffer_t *buffer,
-			  hb_mask_t lookup_mask,
-			  unsigned int context_length,
-			  unsigned int nesting_level_left) const
   {
     unsigned int lookup_type = get_type ();
-    hb_apply_context_t c[1] = {{0}};
-
-    c->font = font;
-    c->face = font->face;
-    c->buffer = buffer;
-    c->direction = buffer->props.direction;
-    c->lookup_mask = lookup_mask;
-    c->context_length = context_length;
-    c->nesting_level_left = nesting_level_left;
-    c->lookup_props = get_props ();
 
     if (!_hb_ot_layout_check_glyph_property (c->face, &c->buffer->info[c->buffer->idx], c->lookup_props, &c->property))
       return false;
@@ -1441,11 +1427,12 @@ struct PosLookup : Lookup
     if (unlikely (!buffer->len))
       return false;
 
+    hb_apply_context_t c (font, font->face, buffer, mask, *this);
+
     buffer->idx = 0;
     while (buffer->idx < buffer->len)
     {
-      if ((buffer->info[buffer->idx].mask & mask) &&
+      if ((buffer->info[buffer->idx].mask & mask) && apply_once (&c))
-	  apply_once (font, buffer, mask, NO_CONTEXT, MAX_NESTING_LEVEL))
 	ret = true;
       else
 	buffer->idx++;
@@ -1598,7 +1585,8 @@ static inline bool position_lookup (hb_apply_context_t *c, unsigned int lookup_i
   if (unlikely (c->context_length < 1))
     return false;
 
-  return l.apply_once (c->font, c->buffer, c->lookup_mask, c->context_length, c->nesting_level_left - 1);
+  hb_apply_context_t new_c (*c, l);
+  return l.apply_once (&new_c);
 }
 
 

src/hb-ot-layout-gsub-table.hh

@@ -754,22 +754,9 @@ struct SubstLookup : Lookup
   }
 
 
-  inline bool apply_once (hb_face_t *face,
+  inline bool apply_once (hb_apply_context_t *c) const
-			  hb_buffer_t *buffer,
-			  hb_mask_t lookup_mask,
-			  unsigned int context_length,
-			  unsigned int nesting_level_left) const
   {
     unsigned int lookup_type = get_type ();
-    hb_apply_context_t c[1] = {{0}};
-
-    c->face = face;
-    c->buffer = buffer;
-    c->direction = buffer->props.direction;
-    c->lookup_mask = lookup_mask;
-    c->context_length = context_length;
-    c->nesting_level_left = nesting_level_left;
-    c->lookup_props = get_props ();
 
     if (!_hb_ot_layout_check_glyph_property (c->face, &c->buffer->info[c->buffer->idx], c->lookup_props, &c->property))
       return false;
@@ -805,6 +792,8 @@ struct SubstLookup : Lookup
     if (unlikely (!buffer->len))
       return false;
 
+    hb_apply_context_t c (NULL, face, buffer, mask, *this);
+
     if (likely (!is_reverse ()))
     {
 	/* in/out forward substitution */
@@ -812,8 +801,7 @@ struct SubstLookup : Lookup
 	buffer->idx = 0;
 	while (buffer->idx < buffer->len)
 	{
-	  if ((buffer->info[buffer->idx].mask & mask) &&
+	  if ((buffer->info[buffer->idx].mask & mask) && apply_once (&c))
-	      apply_once (face, buffer, mask, NO_CONTEXT, MAX_NESTING_LEVEL))
 	    ret = true;
 	  else
 	    buffer->next_glyph ();
@@ -828,8 +816,7 @@ struct SubstLookup : Lookup
 	buffer->idx = buffer->len - 1;
 	do
 	{
-	  if ((buffer->info[buffer->idx].mask & mask) &&
+	  if ((buffer->info[buffer->idx].mask & mask) && apply_once (&c))
-	      apply_once (face, buffer, mask, NO_CONTEXT, MAX_NESTING_LEVEL))
 	    ret = true;
 	  else
 	    buffer->idx--;
@@ -936,7 +923,8 @@ static inline bool substitute_lookup (hb_apply_context_t *c, unsigned int lookup
   if (unlikely (c->context_length < 1))
     return false;
 
-  return l.apply_once (c->face, c->buffer, c->lookup_mask, c->context_length, c->nesting_level_left - 1);
+  hb_apply_context_t new_c (*c, l);
+  return l.apply_once (&new_c);
 }
 
 

src/hb-ot-layout-gsubgpos-private.hh

@@ -67,6 +67,28 @@ struct hb_apply_context_t
   unsigned int lookup_props;
   unsigned int property; /* propety of first glyph */
 
+
+  hb_apply_context_t (hb_font_t *font_,
+		      hb_face_t *face_,
+		      hb_buffer_t *buffer_,
+		      hb_mask_t lookup_mask_,
+		      const Lookup &l,
+		      unsigned int context_length_ = NO_CONTEXT,
+		      unsigned int nesting_level_left_ = MAX_NESTING_LEVEL) :
+			font (font_), face (face_), buffer (buffer_),
+			direction (buffer_->props.direction),
+			lookup_mask (lookup_mask_),
+			context_length (context_length_),
+			nesting_level_left (nesting_level_left_),
+			lookup_props (l.get_props ()),
+			property (0) {}
+
+  hb_apply_context_t (const hb_apply_context_t &c, const Lookup &l) {
+    *this = c;
+    nesting_level_left--;
+    lookup_props = l.get_props ();
+  }
+
   struct mark_skipping_forward_iterator_t
   {
     inline mark_skipping_forward_iterator_t (hb_apply_context_t *c_,