From ca23567f41a2d6389f6fd2483a994cf5aa6aeaf8 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Wed, 7 Nov 2018 16:19:51 -0500
Subject: [PATCH] Disable fallback mark positioning if kern table has
 cross-stream kerning

Happens even if the cross-stream kerning is for cursive attachment only.  Oh well..
---
 src/hb-ot-layout.cc |  6 ++++++
 src/hb-ot-layout.hh |  3 +++
 src/hb-ot-shape.cc  | 14 ++++++--------
 src/hb-ot-shape.hh  |  2 +-
 4 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index 9b93bb085..cdc7755ad 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -63,6 +63,12 @@ hb_ot_layout_has_kerning (hb_face_t *face)
   return face->table.kern->has_data ();
 }
 
+hb_bool_t
+hb_ot_layout_has_cross_kerning (hb_face_t *face)
+{
+  return face->table.kern->has_cross_stream ();
+}
+
 void
 hb_ot_layout_kern (hb_ot_shape_plan_t *plan,
 		   hb_font_t *font,
diff --git a/src/hb-ot-layout.hh b/src/hb-ot-layout.hh
index 437ae4776..ee6e0d254 100644
--- a/src/hb-ot-layout.hh
+++ b/src/hb-ot-layout.hh
@@ -48,6 +48,9 @@ struct hb_ot_shape_plan_t;
 HB_INTERNAL hb_bool_t
 hb_ot_layout_has_kerning (hb_face_t *face);
 
+HB_INTERNAL hb_bool_t
+hb_ot_layout_has_cross_kerning (hb_face_t *face);
+
 HB_INTERNAL void
 hb_ot_layout_kern (hb_ot_shape_plan_t *plan,
 		   hb_font_t *font,
diff --git a/src/hb-ot-shape.cc b/src/hb-ot-shape.cc
index 455c8d689..9b6d47089 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -131,13 +131,12 @@ hb_ot_shape_planner_t::compile (hb_ot_shape_plan_t &plan,
       plan.apply_kerx = true;
     else if (hb_ot_layout_has_kerning (face))
       plan.apply_kern = true;
-    else
-      plan.fallback_kerning = true;
   }
 
+  bool has_kern_mark = plan.apply_kern && hb_ot_layout_has_cross_kerning (face);
+  plan.zero_marks = !plan.apply_kerx && !has_kern_mark;
   plan.has_gpos_mark = !!plan.map.get_1_mask (HB_TAG ('m','a','r','k'));
-  if (!plan.apply_gpos && !plan.apply_kerx)
-    plan.fallback_mark_positioning = true;
+  plan.fallback_mark_positioning = !plan.apply_gpos && !plan.apply_kerx && !has_kern_mark;
 
   /* Currently we always apply trak. */
   plan.apply_trak = plan.requested_tracking && hb_aat_layout_has_tracking (face);
@@ -853,7 +852,7 @@ hb_ot_position_complex (const hb_ot_shape_context_t *c)
 
   hb_ot_layout_position_start (c->font, c->buffer);
 
-  if (!c->plan->apply_kerx)
+  if (c->plan->zero_marks)
     switch (c->plan->shaper->zero_width_marks)
     {
       case HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_EARLY:
@@ -866,20 +865,19 @@ hb_ot_position_complex (const hb_ot_shape_context_t *c)
 	break;
     }
 
-  /* XXX Clean up relationship between these. */
   if (c->plan->apply_gpos)
     c->plan->position (c->font, c->buffer);
   else if (c->plan->apply_kerx)
     hb_aat_layout_position (c->plan, c->font, c->buffer);
   else if (c->plan->apply_kern)
     hb_ot_layout_kern (c->plan, c->font, c->buffer);
-  else if (c->plan->fallback_kerning)
+  else
     _hb_ot_shape_fallback_kern (c->plan, c->font, c->buffer);
 
   if (c->plan->apply_trak)
     hb_aat_layout_track (c->plan, c->font, c->buffer);
 
-  if (!c->plan->apply_kerx)
+  if (c->plan->zero_marks)
     switch (c->plan->shaper->zero_width_marks)
     {
       case HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE:
diff --git a/src/hb-ot-shape.hh b/src/hb-ot-shape.hh
index 1cb9e24d7..655e28d6d 100644
--- a/src/hb-ot-shape.hh
+++ b/src/hb-ot-shape.hh
@@ -51,8 +51,8 @@ struct hb_ot_shape_plan_t
   bool requested_tracking : 1;
   bool has_frac : 1;
   bool has_gpos_mark : 1;
+  bool zero_marks : 1;
   bool fallback_glyph_classes : 1;
-  bool fallback_kerning : 1;
   bool fallback_mark_positioning : 1;
 
   bool apply_gpos : 1;