RenderTextHarfBuzz: Implement font fallback for Win and Linux

ui/gfx/font_fallback_linux.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/font_fallback.h"
+
+#include <fontconfig/fontconfig.h>
+
+namespace gfx {
+
+namespace {
+
+typedef std::map<std::string, std::vector<std::string> > FallbackCache;
+base::LazyInstance<FallbackCache>::Leaky g_fallback_cache =
+    LAZY_INSTANCE_INITIALIZER;
+
+}  // namespace
+
+std::vector<std::string> GetFallbackFontFamilies(std::string font_family) {

[Daniel Erat, 2014/07/14 14:58:20]

in a later change, it may make sense to unify this with the
GetCustomFontRenderParams() code that i'm adding in
https://codereview.chromium.org/382273002/. that method also does a fontconfig
query (but additionally including the size), but returns the primary font
instead of the fallbacks.

PlatformFontPango calls that function to find the primary family to use from the
the list read from a pango description, but perhaps it could call this function
instead or GetCustomFontRenderParams() could be updated to return the full list
of families.

[ckocagil, 2014/07/16 23:42:22]

Acknowledged.

+  std::vector<std::string>* cache_value = &g_fallback_cache.Get()[font_family];
+  if (!cache_value->empty())
+    return *cache_value;
+
+  std::vector<std::string> fallback_fonts;
+
+  FcPattern* pattern = FcPatternCreate();
+  FcValue family;
+  family.type = FcTypeString;
+  family.u.s = reinterpret_cast<const FcChar8*>(font_family.c_str());
+  FcPatternAdd(pattern, FC_FAMILY, family, FcFalse);
+  if (FcConfigSubstitute(NULL, pattern, FcMatchPattern) == FcTrue) {
+    FcDefaultSubstitute(pattern);
+    FcResult result;
+    FcFontSet* fonts = FcFontSort(NULL, pattern, FcTrue, NULL, &result);
+    if (fonts) {
+      for (int i = 0; i < fonts->nfont; ++i) {
+        char* name = NULL;
+        FcPatternGetString(fonts->fonts[i], FC_FAMILY, 0,
+            reinterpret_cast<FcChar8**>(&name));
+        // FontConfig returns multiple fonts with the same family name and
+        // different configurations. Check to prevent duplicate family names.
+        if (fallback_fonts.empty() || fallback_fonts.back() != name)
+          fallback_fonts.push_back(std::string(name));
+      }
+      FcFontSetDestroy(fonts);
+    }
+  }
+  FcPatternDestroy(pattern);
+
+  if (fallback_fonts.empty())
+    fallback_fonts.push_back(font_family);
+
+  *cache_value = fallback_fonts;
+
+  return fallback_fonts;
+}
+
+}  // namespace gfx