RenderTextHarfBuzz: Try fallback fonts of the Uniscribe font while shaping

ui/gfx/render_text_harfbuzz.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/render_text_harfbuzz.h"
 
 #include <limits>
 #include <map>
 
 #include "base/i18n/bidi_line_iterator.h"
@@ skipping 1086 matching lines @@
   FontRenderParams best_render_params;
   size_t best_missing_glyphs = std::numeric_limits<size_t>::max();
 
   if (CompareFamily(run, primary_font.GetFontName(),
                     primary_font.GetFontRenderParams(),
                     &best_family, &best_render_params, &best_missing_glyphs))
     return;
 
 #if defined(OS_WIN)
   Font uniscribe_font;
+  bool got_uniscribe_font = false;
   const base::char16* run_text = &(GetLayoutText()[run->range.start()]);
   if (GetUniscribeFallbackFont(primary_font, run_text, run->range.length(),
-                               &uniscribe_font) &&
-      CompareFamily(run, uniscribe_font.GetFontName(),
-                    uniscribe_font.GetFontRenderParams(),
-                    &best_family, &best_render_params, &best_missing_glyphs))
-    return;
+                               &uniscribe_font)) {
+    got_uniscribe_font = true;
+    if (CompareFamily(run, uniscribe_font.GetFontName(),
+                      uniscribe_font.GetFontRenderParams(),
+                      &best_family, &best_render_params, &best_missing_glyphs))
+      return;
+  }
+#endif
+
+  std::vector<std::string> fallback_families =
+      GetFallbackFontFamilies(primary_font.GetFontName());
+
+#if defined(OS_WIN)
+  // Append fonts in the fallback list of the Uniscribe font.
+  if (got_uniscribe_font) {
+    std::vector<std::string> uniscribe_fallbacks =
+        GetFallbackFontFamilies(uniscribe_font.GetFontName());
+    // Skip the first fallback font, which is |uniscribe_font|.
+    fallback_families.insert(fallback_families.end(),
+        uniscribe_fallbacks.begin() + 1, uniscribe_fallbacks.end());

[Daniel Erat, 2014/10/28 18:00:36]

can the returned vector ever be empty? if so, you probably need to check empty()
here to avoid a crash.

[msw, 2014/10/28 18:17:56]

It looks like all impls should return at least one element. That said, a check
is still a good idea.

[ckocagil, 2014/10/29 01:07:20]

We now add all fonts and skip if it's primary_font or uniscribe_font.

+  }
 #endif
 
   // Skip the first fallback font, which is |primary_font|.

[msw, 2014/10/28 18:17:56]

I'm trying to determine if this is true for font_fallback_linux.cc, which only
adds the primary font if FC doesn't yield any fonts. Is FC guaranteed to include
the argument font as the first in its (otherwise potentially empty) list?

[Daniel Erat, 2014/10/28 18:20:53]

yeah, you're right -- this seems wrong. i don't think there are any guarantees
about what Fontconfig will return here. it could be a completely different set
of fonts.

rather than skipping the first font, we should probably just skip duplicates by
comparing family names against the primary font's family.

[ckocagil, 2014/10/29 01:07:20]

Done.

-  std::vector<std::string> fallback_families =
-      GetFallbackFontFamilies(primary_font.GetFontName());
   for (size_t i = 1; i < fallback_families.size(); ++i) {
     FontRenderParamsQuery query(false);
     query.families.push_back(fallback_families[i]);
     query.pixel_size = run->font_size;
     query.style = run->font_style;
     FontRenderParams fallback_render_params = GetFontRenderParams(query, NULL);
     if (CompareFamily(run, fallback_families[i], fallback_render_params,
                       &best_family, &best_render_params, &best_missing_glyphs))
       return;
   }
@@ skipping 61 matching lines @@
       run->width = std::floor(run->width + 0.5f);
 #endif
   }
 
   hb_buffer_destroy(buffer);
   hb_font_destroy(harfbuzz_font);
   return true;
 }
 
 }  // namespace gfx