Apply TrueType/OpenType kern table when GPOS kern feature is not available

Fixes https://github.com/harfbuzz/harfbuzz/issues/250

src/hb-ot-kern-table.hh

@@ -37,14 +37,11 @@ struct hb_kern_machine_t
 {
   hb_kern_machine_t (const Driver &driver_) : driver (driver_) {}
 
-  inline void kern (const hb_ot_shape_plan_t *plan,
-		    hb_font_t *font,
-		    hb_buffer_t  *buffer) const
+  inline void kern (hb_font_t *font,
+		    hb_buffer_t  *buffer,
+		    hb_mask_t kern_mask) const
   {
-    if (!plan->kerning_requested) return;
-
     OT::hb_ot_apply_context_t c (1, font, buffer);
-    hb_mask_t kern_mask = plan->kern_mask;
     c.set_lookup_mask (kern_mask);
     c.set_lookup_props (OT::LookupFlag::IgnoreMarks);
     OT::hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c.iter_input;
@@ -411,6 +408,9 @@ struct kern
 {
   static const hb_tag_t tableTag = HB_OT_TAG_kern;
 
+  inline bool has_data (void) const
+  { return u.version32 != 0; }
+
   inline int get_h_kerning (hb_codepoint_t left, hb_codepoint_t right, unsigned int table_length) const
   {
     switch (u.major) {
@@ -444,22 +444,25 @@ struct kern
       hb_blob_destroy (blob);
     }
 
+    inline bool has_data (void) const
+    { return table->has_data (); }
+
     inline int get_h_kerning (hb_codepoint_t left, hb_codepoint_t right) const
     { return table->get_h_kerning (left, right, table_length); }
 
     inline int get_kerning (hb_codepoint_t first, hb_codepoint_t second) const
     { return get_h_kerning (first, second); }
 
-    inline void apply (hb_ot_shape_plan_t *plan,
-		       hb_font_t *font,
-		       hb_buffer_t  *buffer) const
+    inline void apply (hb_font_t *font,
+		       hb_buffer_t  *buffer,
+		       hb_mask_t kern_mask) const
     {
       if (!HB_DIRECTION_IS_HORIZONTAL (buffer->props.direction))
         return;
 
       hb_kern_machine_t<accelerator_t> machine (*this);
 
-      machine.kern (plan, font, buffer);
+      machine.kern (font, buffer, kern_mask);
     }
 
     private:
@@ -471,6 +474,7 @@ struct kern
   protected:
   union {
   HBUINT16		major;
+  HBUINT32		version32;
   KernOT		ot;
   KernAAT		aat;
   } u;

src/hb-ot-layout.cc

@@ -45,17 +45,15 @@
 #include "hb-ot-color-cpal-table.hh"
 #include "hb-ot-color-sbix-table.hh"
 #include "hb-ot-color-svg-table.hh"
+#include "hb-ot-kern-table.hh"
 #include "hb-ot-name-table.hh"
 
 
-// static inline const OT::BASE&
-// _get_base (hb_face_t *face)
-// {
-//   if (unlikely (!hb_ot_shaper_face_data_ensure (face))) return Null(OT::BASE);
-//   hb_ot_face_data_t *data = hb_ot_face_data (face);
-//   return *(data->base.get ());
-// }
-
+static const OT::kern::accelerator_t& _get_kern (hb_face_t *face)
+{
+  if (unlikely (!hb_ot_shaper_face_data_ensure (face))) return Null(OT::kern::accelerator_t);
+  return *hb_ot_face_data (face)->kern;
+}
 const OT::GDEF& _get_gdef (hb_face_t *face)
 {
   if (unlikely (!hb_ot_shaper_face_data_ensure (face))) return Null(OT::GDEF);
@@ -91,6 +89,25 @@ const OT::GPOS& _get_gpos_relaxed (hb_face_t *face)
 }
 
 
+/*
+ * kern
+ */
+
+hb_bool_t
+hb_ot_layout_has_kerning (hb_face_t *face)
+{
+  return _get_kern (face).has_data ();
+}
+
+void
+hb_ot_layout_kern (hb_font_t *font,
+		   hb_buffer_t  *buffer,
+		   hb_mask_t kern_mask)
+{
+  _get_kern (font->face).apply (font, buffer, kern_mask);
+}
+
+
 /*
  * GDEF
  */
@@ -1306,27 +1323,3 @@ hb_ot_layout_substitute_lookup (OT::hb_ot_apply_context_t *c,
 {
   apply_string<GSUBProxy> (c, lookup, accel);
 }
-
-
-
-
-/*
- * OT::BASE
- */
-
-// /**
-//  * hb_ot_base_has_data:
-//  * @face: #hb_face_t to test
-//  *
-//  * This function allows to verify the presence of an OpenType BASE table on the
-//  * face.
-//  *
-//  * Return value: true if face has a BASE table, false otherwise
-//  *
-//  * Since: XXX
-//  **/
-// hb_bool_t
-// hb_ot_base_has_data (hb_face_t *face)
-// {
-//   return _get_base (face).has_data ();
-// }

src/hb-ot-layout.hh

@@ -49,6 +49,19 @@ HB_INTERNAL const OT::GSUB& _get_gsub_relaxed (hb_face_t *face);
 HB_INTERNAL const OT::GPOS& _get_gpos_relaxed (hb_face_t *face);
 
 
+/*
+ * kern
+ */
+
+HB_INTERNAL hb_bool_t
+hb_ot_layout_has_kerning (hb_face_t *face);
+
+HB_INTERNAL void
+hb_ot_layout_kern (hb_font_t *font,
+		   hb_buffer_t  *buffer,
+		   hb_mask_t kern_mask);
+
+
 /* Private API corresponding to hb-ot-layout.h: */
 
 HB_INTERNAL hb_bool_t

src/hb-ot-shape-fallback.cc

@@ -439,7 +439,7 @@ _hb_ot_shape_fallback_mark_position (const hb_ot_shape_plan_t *plan,
 void
 _hb_ot_shape_fallback_kern (const hb_ot_shape_plan_t *plan,
 			    hb_font_t *font,
-			    hb_buffer_t  *buffer)
+			    hb_buffer_t *buffer)
 {
   struct driver_t
   {
@@ -462,7 +462,7 @@ _hb_ot_shape_fallback_kern (const hb_ot_shape_plan_t *plan,
 
   hb_kern_machine_t<driver_t> machine (driver);
 
-  machine.kern (plan, font, buffer);
+  machine.kern (font, buffer, plan->kern_mask);
 }
 
 

src/hb-ot-shape.cc

@@ -69,8 +69,8 @@ hb_ot_shape_planner_t::compile (hb_ot_shape_plan_t &plan,
   bool disable_gpos = plan.shaper->gpos_tag &&
 		      plan.shaper->gpos_tag != plan.map.chosen_script[1];
   plan.apply_gpos = !disable_gpos && hb_ot_layout_has_positioning (face);
-
-  plan.fallback_kerning = !plan.apply_gpos;
+  plan.apply_kern = !plan.apply_gpos && hb_ot_layout_has_kerning (face);
+  plan.fallback_kerning = !plan.apply_gpos && !plan.apply_kern;
   plan.fallback_mark_positioning = !plan.apply_gpos;
   plan.fallback_glyph_classes = !hb_ot_layout_has_glyph_classes (face);
 }
@@ -835,7 +835,11 @@ hb_ot_position (const hb_ot_shape_context_t *c)
 
   /* Visual fallback goes here. */
 
-  if (c->plan->fallback_kerning)
+  if (!c->plan->kerning_requested)
+    ;
+  else if (c->plan->apply_kern)
+    hb_ot_layout_kern (c->font, c->buffer, c->plan->kern_mask);
+  else if (c->plan->fallback_kerning)
     _hb_ot_shape_fallback_kern (c->plan, c->font, c->buffer);
 
   _hb_buffer_deallocate_gsubgpos_vars (c->buffer);

src/hb-ot-shape.hh

@@ -51,6 +51,7 @@ struct hb_ot_shape_plan_t
   bool fallback_mark_positioning : 1;
 
   bool apply_morx : 1;
+  bool apply_kern : 1;
   bool apply_gpos : 1;