From 683c3a95330928129cfbb1488650f708414d68ba Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 8 Oct 2018 23:09:48 -0400
Subject: [PATCH] [kern] Abstract away kerning machine

---
 src/hb-font.hh              |  2 +-
 src/hb-ot-kern-table.hh     | 71 +++++++++++++++++++++++++++++++++++++
 src/hb-ot-shape-fallback.cc | 69 ++++++++++-------------------------
 3 files changed, 90 insertions(+), 52 deletions(-)

diff --git a/src/hb-font.hh b/src/hb-font.hh
index 4c8d0aeec..8b19dd715 100644
--- a/src/hb-font.hh
+++ b/src/hb-font.hh
@@ -502,8 +502,8 @@ struct hb_font_t
 					       hb_position_t *x, hb_position_t *y)
   {
     if (likely (HB_DIRECTION_IS_HORIZONTAL (direction))) {
-      *x = get_glyph_h_kerning (first_glyph, second_glyph);
       *y = 0;
+      *x = get_glyph_h_kerning (first_glyph, second_glyph);
     } else {
       *x = 0;
       *y = get_glyph_v_kerning (first_glyph, second_glyph);
diff --git a/src/hb-ot-kern-table.hh b/src/hb-ot-kern-table.hh
index e33b17396..f7c2ed380 100644
--- a/src/hb-ot-kern-table.hh
+++ b/src/hb-ot-kern-table.hh
@@ -28,6 +28,77 @@
 #define HB_OT_KERN_TABLE_HH
 
 #include "hb-open-type.hh"
+#include "hb-ot-shape.hh"
+#include "hb-ot-layout-gsubgpos.hh"
+
+
+template <typename Driver>
+struct hb_kern_machine_t
+{
+  hb_kern_machine_t (Driver &driver_) : driver (driver_) {}
+
+  inline void kern (const hb_ot_shape_plan_t *plan,
+		    hb_font_t *font,
+		    hb_buffer_t  *buffer) 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;
+    skippy_iter.init (&c);
+
+    bool horizontal = HB_DIRECTION_IS_HORIZONTAL (buffer->props.direction);
+    unsigned int count = buffer->len;
+    hb_glyph_info_t *info = buffer->info;
+    hb_glyph_position_t *pos = buffer->pos;
+    for (unsigned int idx = 0; idx < count;)
+    {
+      if (!(info[idx].mask & kern_mask))
+      {
+	idx++;
+	continue;
+      }
+
+      skippy_iter.reset (idx, 1);
+      if (!skippy_iter.next ())
+      {
+	idx++;
+	continue;
+      }
+
+      unsigned int i = idx;
+      unsigned int j = skippy_iter.idx;
+      hb_position_t kern = driver.get_kerning (info[i].codepoint,
+					       info[j].codepoint);
+
+      hb_position_t kern1 = kern >> 1;
+      hb_position_t kern2 = kern - kern1;
+
+      if (horizontal)
+      {
+	pos[i].x_advance += kern1;
+	pos[j].x_advance += kern2;
+	pos[j].x_offset += kern2;
+      }
+      else
+      {
+	pos[i].y_advance += kern1;
+	pos[j].y_advance += kern2;
+	pos[j].y_offset += kern2;
+      }
+
+      buffer->unsafe_to_break (i, j + 1);
+
+      idx = skippy_iter.idx;
+    }
+  }
+
+  Driver &driver;
+};
+
 
 /*
  * kern -- Kerning
diff --git a/src/hb-ot-shape-fallback.cc b/src/hb-ot-shape-fallback.cc
index 6673abd14..920ef22c6 100644
--- a/src/hb-ot-shape-fallback.cc
+++ b/src/hb-ot-shape-fallback.cc
@@ -25,7 +25,7 @@
  */
 
 #include "hb-ot-shape-fallback.hh"
-#include "hb-ot-layout-gsubgpos.hh"
+#include "hb-ot-kern-table.hh"
 
 static unsigned int
 recategorize_combining_class (hb_codepoint_t u,
@@ -435,67 +435,34 @@ _hb_ot_shape_fallback_position (const hb_ot_shape_plan_t *plan,
 }
 
 
-/* Performs old-style TrueType kerning. */
+/* Performs font-assisted kerning. */
 void
 _hb_ot_shape_fallback_kern (const hb_ot_shape_plan_t *plan,
 			    hb_font_t *font,
 			    hb_buffer_t  *buffer)
 {
-  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;
-  skippy_iter.init (&c);
-
-  unsigned int count = buffer->len;
-  hb_glyph_info_t *info = buffer->info;
-  hb_glyph_position_t *pos = buffer->pos;
-  for (unsigned int idx = 0; idx < count;)
+  struct driver_t
   {
-    if (!(info[idx].mask & kern_mask))
+    driver_t (hb_font_t   *font_,
+	      hb_buffer_t *buffer) :
+      font (font_), direction (buffer->props.direction) {}
+
+    hb_position_t get_kerning (hb_codepoint_t first, hb_codepoint_t second)
     {
-      idx++;
-      continue;
+      hb_position_t kern = 0;
+      font->get_glyph_kerning_for_direction (first, second,
+					     direction,
+					     &kern, &kern);
+      return kern;
     }
 
-    skippy_iter.reset (idx, 1);
-    if (!skippy_iter.next ())
-    {
-      idx++;
-      continue;
-    }
+    hb_font_t *font;
+    hb_direction_t direction;
+  } driver (font, buffer);
 
-    hb_position_t x_kern, y_kern;
-    font->get_glyph_kerning_for_direction (info[idx].codepoint,
-					   info[skippy_iter.idx].codepoint,
-					   buffer->props.direction,
-					   &x_kern, &y_kern);
+  hb_kern_machine_t<driver_t> machine (driver);
 
-    if (x_kern)
-    {
-      hb_position_t kern1 = x_kern >> 1;
-      hb_position_t kern2 = x_kern - kern1;
-      pos[idx].x_advance += kern1;
-      pos[skippy_iter.idx].x_advance += kern2;
-      pos[skippy_iter.idx].x_offset += kern2;
-      buffer->unsafe_to_break (idx, skippy_iter.idx + 1);
-    }
-
-    if (y_kern)
-    {
-      hb_position_t kern1 = y_kern >> 1;
-      hb_position_t kern2 = y_kern - kern1;
-      pos[idx].y_advance += kern1;
-      pos[skippy_iter.idx].y_advance += kern2;
-      pos[skippy_iter.idx].y_offset += kern2;
-      buffer->unsafe_to_break (idx, skippy_iter.idx + 1);
-    }
-
-    idx = skippy_iter.idx;
-  }
+  machine.kern (plan, font, buffer);
 }