[MATH] Clean up get_top_accent_attachment()

Note, the function now returns "half of horizontal advance width"
if top accent attachment for glyph is not explicitly defined.
This is what the spec requires.  Updated tests.

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

@@ -178,7 +178,6 @@ struct MathItalicsCorrectionInfo
   {
     unsigned int index = (this+coverage).get_coverage (glyph);
     return italicsCorrection[index].get_x_value (font, this);
-    return true;
   }
 
 protected:
@@ -205,14 +204,13 @@ struct MathTopAccentAttachment
 		  topAccentAttachment.sanitize (c, this));
   }
 
-  inline bool get_value (hb_font_t *font, hb_codepoint_t glyph,
-			 hb_position_t &value) const
+  inline hb_position_t get_value (hb_codepoint_t glyph,
+				  hb_font_t *font) const
   {
     unsigned int index = (this+topAccentCoverage).get_coverage (glyph);
-    if (likely (index == NOT_COVERED)) return false;
-    if (unlikely (index >= topAccentAttachment.len)) return false;
-    value = topAccentAttachment[index].get_x_value(font, this);
-    return true;
+    if (index == NOT_COVERED)
+      return font->get_glyph_h_advance (glyph) / 2;
+    return topAccentAttachment[index].get_x_value(font, this);
   }
 
 protected:
@@ -366,22 +364,15 @@ struct MathGlyphInfo
   }
 
   inline hb_position_t
-  get_italics_correction (hb_codepoint_t glyph,
-			  hb_font_t *font) const
-  {
-    return (this+mathItalicsCorrectionInfo).get_value (glyph, font);
-  }
+  get_italics_correction (hb_codepoint_t  glyph, hb_font_t *font) const
+  { return (this+mathItalicsCorrectionInfo).get_value (glyph, font); }
 
-  inline const MathTopAccentAttachment&
-  get_math_top_accent_attachment (void) const {
-    return this+mathTopAccentAttachment;
-  }
+  inline hb_position_t
+  get_top_accent_attachment (hb_codepoint_t  glyph, hb_font_t *font) const
+  { return (this+mathTopAccentAttachment).get_value (glyph, font); }
 
   inline bool is_extended_shape (hb_codepoint_t glyph) const
-  {
-    unsigned int index = (this+extendedShapeCoverage).get_coverage (glyph);
-    return index != NOT_COVERED;
-  }
+  { return (this+extendedShapeCoverage).get_coverage (glyph) != NOT_COVERED; }
 
   inline const MathKernInfo &get_math_kern_info (void) const {
     return this+mathKernInfo;

src/hb-ot-layout.cc

@@ -1302,12 +1302,7 @@ hb_ot_layout_get_math_top_accent_attachment (hb_font_t *font,
 					     hb_codepoint_t glyph)
 {
   const OT::MATH &math = _get_math (font->face);
-  const OT::MathGlyphInfo &glyphInfo = math.get_math_glyph_info();
-  hb_position_t value;
-  if (glyphInfo.get_math_top_accent_attachment().get_value(font, glyph, value))
-    return value;
-  else
-    return 0; // XXX font->get_glyph_h_advance (glyph) / 2;
+  return math.get_math_glyph_info().get_top_accent_attachment (glyph, font);
 }
 
 /**

test/api/test-ot-layout-math.c

@@ -204,22 +204,22 @@ test_get_math_top_accent_attachment (void)
 
   openFont("fonts/MathTestFontEmpty.otf");
   g_assert(hb_font_get_glyph_from_name (hb_font, "space", -1, &glyph));
-  g_assert_cmpint(hb_ot_layout_get_math_top_accent_attachment (hb_font, glyph), ==, 0); // MathGlyphInfo not available
+  g_assert_cmpint(hb_ot_layout_get_math_top_accent_attachment (hb_font, glyph), ==, 500); // MathGlyphInfo not available
   closeFont();
 
   openFont("fonts/MathTestFontPartial1.otf");
   g_assert(hb_font_get_glyph_from_name (hb_font, "space", -1, &glyph));
-  g_assert_cmpint(hb_ot_layout_get_math_top_accent_attachment (hb_font, glyph), ==, 0); // MathGlyphInfo empty
+  g_assert_cmpint(hb_ot_layout_get_math_top_accent_attachment (hb_font, glyph), ==, 500); // MathGlyphInfo empty
   closeFont();
 
   openFont("fonts/MathTestFontPartial2.otf");
   g_assert(hb_font_get_glyph_from_name (hb_font, "space", -1, &glyph));
-  g_assert_cmpint(hb_ot_layout_get_math_top_accent_attachment (hb_font, glyph), ==, 0); // MathTopAccentAttachment empty
+  g_assert_cmpint(hb_ot_layout_get_math_top_accent_attachment (hb_font, glyph), ==, 500); // MathTopAccentAttachment empty
   closeFont();
 
   openFont("fonts/MathTestFontFull.otf");
   g_assert(hb_font_get_glyph_from_name (hb_font, "space", -1, &glyph));
-  g_assert_cmpint(hb_ot_layout_get_math_top_accent_attachment (hb_font, glyph), ==, 0); // Glyph without top accent attachment.
+  g_assert_cmpint(hb_ot_layout_get_math_top_accent_attachment (hb_font, glyph), ==, 500); // Glyph without top accent attachment.
   g_assert(hb_font_get_glyph_from_name (hb_font, "D", -1, &glyph));
   g_assert_cmpint(hb_ot_layout_get_math_top_accent_attachment (hb_font, glyph), ==, 374);
   g_assert(hb_font_get_glyph_from_name (hb_font, "E", -1, &glyph));