Normalize various spaces to space if font doesn't support

This resurrects the space fallback feature, after I disabled
the compatibility decomposition.  Now I can release HarfBuzz
again without breaking Pango!

It also remembers which space character it was, such that later
on we can approximate the width of this particular space
character.  That part is not implemented yet.

We normalize all GC=Zs chars except for U+1680 OGHA SPACE MARK,
which is better left alone.

src/hb-ot-layout-private.hh

@@ -237,23 +237,6 @@ enum {
   UPROPS_MASK_GEN_CAT   = 0x1Fu
 };
 
-enum space_t {
-  SPACE = 0,
-  SPACE_NBSP,
-  SPACE_EN,
-  SPACE_EM,
-  SPACE_EM_3,
-  SPACE_EM_4,
-  SPACE_EM_6,
-  SPACE_FIGURE,
-  SPACE_PUNCTUATION,
-  SPACE_THIN,
-  SPACE_HAIR,
-  SPACE_NARROW,
-  SPACE_MEDIUM,
-  SPACE_IDEOGRAPHIC,
-};
-
 static inline void
 _hb_glyph_info_set_unicode_props (hb_glyph_info_t *info, hb_unicode_funcs_t *unicode)
 {
@@ -331,36 +314,18 @@ _hb_glyph_info_is_unicode_space (const hb_glyph_info_t *info)
 	 HB_UNICODE_GENERAL_CATEGORY_SPACE_SEPARATOR;
 }
 static inline void
-_hb_glyph_info_set_unicode_space_for_char (hb_glyph_info_t *info, hb_codepoint_t u)
+_hb_glyph_info_set_unicode_space_fallback_type (hb_glyph_info_t *info, hb_unicode_funcs_t::space_t s)
 {
   if (unlikely (!_hb_glyph_info_is_unicode_space (info)))
     return;
-
-  space_t s;
-  switch (u)
-  {
-    default:      s = SPACE;		break; /* Shouldn't happen. */
-    case 0x00A0u: s = SPACE_NBSP;	break;
-    case 0x2002u: s = SPACE_EN;		break;
-    case 0x2003u: s = SPACE_EM;		break;
-    case 0x2004u: s = SPACE_EM_3;	break;
-    case 0x2005u: s = SPACE_EM_4;	break;
-    case 0x2006u: s = SPACE_EM_6;	break;
-    case 0x2007u: s = SPACE_FIGURE;	break;
-    case 0x2008u: s = SPACE_PUNCTUATION;break;
-    case 0x2009u: s = SPACE_THIN;	break;
-    case 0x200Au: s = SPACE_HAIR;	break;
-    case 0x202Fu: s = SPACE_NARROW;	break;
-    case 0x205Fu: s = SPACE_MEDIUM;	break;
-    case 0x3000u: s = SPACE_IDEOGRAPHIC;break;
-  }
-
   info->unicode_props() = (((unsigned int) s)<<8) | (info->unicode_props() & 0xFF);
 }
-static inline space_t
-_hb_glyph_info_get_unicode_space (const hb_glyph_info_t *info)
+static inline hb_unicode_funcs_t::space_t
+_hb_glyph_info_get_unicode_space_fallback_type (const hb_glyph_info_t *info)
 {
-  return _hb_glyph_info_is_unicode_space (info) ? (space_t) (info->unicode_props()>>8) : SPACE;
+  return _hb_glyph_info_is_unicode_space (info) ?
+	 (hb_unicode_funcs_t::space_t) (info->unicode_props()>>8) :
+	 hb_unicode_funcs_t::NOT_SPACE;
 }
 
 static inline bool _hb_glyph_info_ligated (const hb_glyph_info_t *info);

src/hb-ot-shape-normalize.cc

@@ -98,7 +98,7 @@ static inline void
 output_char (hb_buffer_t *buffer, hb_codepoint_t unichar, hb_codepoint_t glyph)
 {
   buffer->cur().glyph_index() = glyph;
-  buffer->output_glyph (unichar);
+  buffer->output_glyph (unichar); /* This is very confusing indeed. */
   _hb_glyph_info_set_unicode_props (&buffer->prev(), buffer->unicode);
 }
 
@@ -164,7 +164,8 @@ decompose_current_character (const hb_ot_shape_normalize_context_t *c, bool shor
 {
   hb_buffer_t * const buffer = c->buffer;
   hb_codepoint_t u = buffer->cur().codepoint;
-  hb_codepoint_t glyph;
+  hb_codepoint_t glyph, space_glyph;
+  hb_unicode_funcs_t::space_t space_type;
 
   /* Kind of a cute waterfall here... */
   if (shortest && c->font->get_glyph (u, 0, &glyph))
@@ -173,6 +174,13 @@ decompose_current_character (const hb_ot_shape_normalize_context_t *c, bool shor
     skip_char (buffer);
   else if (!shortest && c->font->get_glyph (u, 0, &glyph))
     next_char (buffer, glyph);
+  else if (_hb_glyph_info_is_unicode_space (&buffer->cur()) &&
+	   (space_type = buffer->unicode->space_fallback_type (u)) != hb_unicode_funcs_t::NOT_SPACE &&
+	   c->font->get_glyph (0x0020u, 0, &space_glyph))
+  {
+    _hb_glyph_info_set_unicode_space_fallback_type (&buffer->cur(), space_type);
+    next_char (buffer, space_glyph);
+  }
   else
     next_char (buffer, glyph); /* glyph is initialized in earlier branches. */
 }

src/hb-unicode-private.hh

@@ -199,6 +199,46 @@ HB_UNICODE_FUNCS_IMPLEMENT_CALLBACKS_SIMPLE
     }
   }
 
+  enum space_t {
+    NOT_SPACE = 0,
+    SPACE_NBSP,
+    SPACE_EN,
+    SPACE_EM,
+    SPACE_EM_3,
+    SPACE_EM_4,
+    SPACE_EM_6,
+    SPACE_FIGURE,
+    SPACE_PUNCTUATION,
+    SPACE_THIN,
+    SPACE_HAIR,
+    SPACE_NARROW,
+    SPACE_MEDIUM,
+    SPACE_IDEOGRAPHIC,
+  };
+  static inline space_t
+  space_fallback_type (hb_codepoint_t u)
+  {
+    switch (u)
+    {
+      /* All GC=Zs chars that can use a fallback. */
+      default:	  return NOT_SPACE; /* Shouldn't happen. */
+      case 0x00A0u: return SPACE_NBSP;
+      case 0x2000u: return SPACE_EN;
+      case 0x2001u: return SPACE_EM;
+      case 0x2002u: return SPACE_EN;
+      case 0x2003u: return SPACE_EM;
+      case 0x2004u: return SPACE_EM_3;
+      case 0x2005u: return SPACE_EM_4;
+      case 0x2006u: return SPACE_EM_6;
+      case 0x2007u: return SPACE_FIGURE;
+      case 0x2008u: return SPACE_PUNCTUATION;
+      case 0x2009u: return SPACE_THIN;
+      case 0x200Au: return SPACE_HAIR;
+      case 0x202Fu: return SPACE_NARROW;
+      case 0x205Fu: return SPACE_MEDIUM;
+      case 0x3000u: return SPACE_IDEOGRAPHIC;
+    }
+  }
 
   struct {
 #define HB_UNICODE_FUNC_IMPLEMENT(name) hb_unicode_##name##_func_t name;

test/shaping/Makefile.am

@@ -52,6 +52,7 @@ TESTS = \
 	tests/indic-old-spec.tests \
 	tests/indic-pref-blocking.tests \
 	tests/mongolian-variation-selector.tests \
+	tests/spaces.tests \
 	tests/vertical.tests \
 	tests/zero-width-marks.tests \
 	$(NULL)

test/shaping/fonts/sha1sum/MANIFEST

@@ -2,6 +2,7 @@
 051d92f8bc6ff724511b296c27623f824de256e9.ttf
 191826b9643e3f124d865d617ae609db6a2ce203.ttf
 1a6f1687b7a221f9f2c834b0b360d3c8463b6daf.ttf
+1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf
 226bc2deab3846f1a682085f70c67d0421014144.ttf
 270b89df543a7e48e206a2d830c0e10e5265c630.ttf
 298c9e1d955f10f6f72c6915c3c6ff9bf9695cec.ttf

test/shaping/tests/MANIFEST

@@ -10,5 +10,6 @@ indic-joiner-candrabindu.tests
 indic-old-spec.tests
 indic-pref-blocking.tests
 mongolian-variation-selector.tests
+spaces.tests
 vertical.tests
 zero-width-marks.tests

test/shaping/tests/spaces.tests

+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+0020:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+00A0:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+1680:[gid0=0+692]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+2000:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+2001:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+2002:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+2003:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+2004:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+2005:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+2006:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+2007:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+2008:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+2009:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+200A:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+202F:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+205F:[gid1=0+560]
+fonts/sha1sum/1c2c3fc37b2d4c3cb2ef726c6cdaaabd4b7f3eb9.ttf:--font-funcs=ot:U+3000:[gid1=0+560]