[API] Make get_glyph() callback return a boolean

We need to know whether the glyph exists, so we can fallback to
composing / decomposing.  Assuming that glyph==0 means "doesn't exist"
wouldn't work for applications like Pango that want to use different
"doesn't exist" glyph codes for different characters.  An explicit
return value fixes that.

src/hb-font.cc

@@ -99,17 +99,19 @@ hb_font_get_glyph_extents_nil (hb_font_t *font HB_UNUSED,
   extents->width = extents->height = 0;
 }
 
-static hb_codepoint_t
+static hb_bool_t
 hb_font_get_glyph_nil (hb_font_t *font HB_UNUSED,
 		       void *font_data HB_UNUSED,
 		       hb_codepoint_t unicode,
 		       hb_codepoint_t variation_selector,
+		       hb_codepoint_t *glyph,
 		       void *user_data HB_UNUSED)
 {
   if (font->parent)
-    return hb_font_get_glyph (font->parent, unicode, variation_selector);
+    return hb_font_get_glyph (font->parent, unicode, variation_selector, glyph);
 
-  return 0;
+  *glyph = 0;
+  return FALSE;
 }
 
 static void
@@ -287,12 +289,13 @@ hb_font_get_glyph_extents (hb_font_t *font,
 					 font->klass->user_data.glyph_extents);
 }
 
-hb_codepoint_t
+hb_bool_t
 hb_font_get_glyph (hb_font_t *font,
-		   hb_codepoint_t unicode, hb_codepoint_t variation_selector)
+		   hb_codepoint_t unicode, hb_codepoint_t variation_selector,
+		   hb_codepoint_t *glyph)
 {
   return font->klass->get.glyph (font, font->user_data,
-				 unicode, variation_selector,
+				 unicode, variation_selector, glyph,
 				 font->klass->user_data.glyph);
 }
 

src/hb-font.h

@@ -140,8 +140,9 @@ typedef void (*hb_font_get_glyph_extents_func_t) (hb_font_t *font, void *font_da
 						  hb_codepoint_t glyph,
 						  hb_glyph_extents_t *extents,
 						  void *user_data);
-typedef hb_codepoint_t (*hb_font_get_glyph_func_t) (hb_font_t *font, void *font_data,
+typedef hb_bool_t (*hb_font_get_glyph_func_t) (hb_font_t *font, void *font_data,
 					       hb_codepoint_t unicode, hb_codepoint_t variation_selector,
+					       hb_codepoint_t *glyph,
 					       void *user_data);
 typedef void (*hb_font_get_kerning_func_t) (hb_font_t *font, void *font_data,
 					    hb_codepoint_t left_glyph, hb_codepoint_t right_glyph,
@@ -190,9 +191,10 @@ hb_font_get_glyph_extents (hb_font_t *font,
 			   hb_codepoint_t glyph,
 			   hb_glyph_extents_t *extents);
 
-hb_codepoint_t
+hb_bool_t
 hb_font_get_glyph (hb_font_t *font,
-		   hb_codepoint_t unicode, hb_codepoint_t variation_selector);
+		   hb_codepoint_t unicode, hb_codepoint_t variation_selector,
+		   hb_codepoint_t *glyph);
 
 void
 hb_font_get_kerning (hb_font_t *font,

src/hb-ft.cc

@@ -107,11 +107,12 @@ hb_ft_get_glyph_extents (hb_font_t *font HB_UNUSED,
   }
 }
 
-static hb_codepoint_t
+static hb_bool_t
 hb_ft_get_glyph (hb_font_t *font HB_UNUSED,
 		 void *font_data,
 		 hb_codepoint_t unicode,
 		 hb_codepoint_t variation_selector,
+		 hb_codepoint_t *glyph,
 		 void *user_data HB_UNUSED)
 
 {
@@ -119,13 +120,14 @@ hb_ft_get_glyph (hb_font_t *font HB_UNUSED,
 
 #ifdef HAVE_FT_FACE_GETCHARVARIANTINDEX
   if (unlikely (variation_selector)) {
-    hb_codepoint_t glyph = FT_Face_GetCharVariantIndex (ft_face, unicode, variation_selector);
-    if (glyph)
-      return glyph;
+    *glyph = FT_Face_GetCharVariantIndex (ft_face, unicode, variation_selector);
+    if (*glyph)
+      return TRUE;
   }
 #endif
 
-  return FT_Get_Char_Index (ft_face, unicode);
+  *glyph = FT_Get_Char_Index (ft_face, unicode);
+  return *glyph != 0;
 }
 
 static void

src/hb-ot-shape.cc

@@ -216,18 +216,23 @@ hb_map_glyphs (hb_font_t    *font,
   if (unlikely (!buffer->len))
     return;
 
+  hb_codepoint_t glyph;
   buffer->clear_output ();
   unsigned int count = buffer->len - 1;
   for (buffer->i = 0; buffer->i < count;) {
     if (unlikely (is_variation_selector (buffer->info[buffer->i + 1].codepoint))) {
-      buffer->replace_glyph (hb_font_get_glyph (font, buffer->info[buffer->i].codepoint, buffer->info[buffer->i + 1].codepoint));
+      hb_font_get_glyph (font, buffer->info[buffer->i].codepoint, buffer->info[buffer->i + 1].codepoint, &glyph);
+      buffer->replace_glyph (glyph);
       buffer->i++;
     } else {
-      buffer->replace_glyph (hb_font_get_glyph (font, buffer->info[buffer->i].codepoint, 0));
+      hb_font_get_glyph (font, buffer->info[buffer->i].codepoint, 0, &glyph);
+      buffer->replace_glyph (glyph);
     }
   }
-  if (likely (buffer->i < buffer->len))
-    buffer->replace_glyph (hb_font_get_glyph (font, buffer->info[buffer->i].codepoint, 0));
+  if (likely (buffer->i < buffer->len)) {
+    hb_font_get_glyph (font, buffer->info[buffer->i].codepoint, 0, &glyph);
+    buffer->replace_glyph (glyph);
+  }
   buffer->swap ();
 }
 

test/test-font.c

@@ -112,6 +112,7 @@ test_face_createfortables (void)
 static void
 _test_font_nil_funcs (hb_font_t *font)
 {
+  hb_codepoint_t glyph;
   hb_position_t x, y;
   hb_glyph_extents_t extents;
 
@@ -133,7 +134,9 @@ _test_font_nil_funcs (hb_font_t *font)
   g_assert_cmpint (extents.width, ==, 0);
   g_assert_cmpint (extents.height, ==, 0);
 
-  g_assert (0 == hb_font_get_glyph (font, 17, 2));
+  glyph = 3;
+  g_assert (!hb_font_get_glyph (font, 17, 2, &glyph));
+  g_assert_cmpint (glyph, ==, 0);
 
   x = y = 13;
   hb_font_get_kerning (font, 17, 19, &x, &y);

test/test-shape.c

@@ -44,17 +44,19 @@ glyph_advance_func (hb_font_t *font, void *font_data,
   }
 }
 
-static hb_codepoint_t
+static hb_bool_t
 glyph_func (hb_font_t *font, void *font_data,
 	    hb_codepoint_t unicode, hb_codepoint_t variant_selector,
+	    hb_codepoint_t *glyph,
 	    void *user_data)
 {
   switch (unicode) {
-  case 'T': return 1;
-  case 'e': return 2;
-  case 's': return 3;
-  default:  return 0;
+  case 'T': *glyph = 1; return TRUE;
+  case 'e': *glyph = 2; return TRUE;
+  case 's': *glyph = 3; return TRUE;
   }
+
+  return FALSE;
 }
 
 static void