Disable subpixel positioning if DirectWrite isn't initialized

ui/gfx/win/direct_write.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/win/direct_write.h"
 
 #include <dwrite.h>
 
 #include "base/basictypes.h"
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
 #include "base/win/registry.h"
 #include "base/win/scoped_comptr.h"
 #include "base/win/windows_version.h"
 #include "skia/ext/fontmgr_default_win.h"
 #include "third_party/skia/include/ports/SkTypeface_win.h"
 #include "ui/gfx/platform_font_win.h"
 #include "ui/gfx/switches.h"
 #include "ui/gfx/win/dpi.h"
 
 namespace gfx {
 namespace win {
 
+namespace {
+
+static bool dwrite_enabled = false;
+
+}
+
 bool ShouldUseDirectWrite() {
   // If the flag is currently on, and we're on Win7 or above, we enable
   // DirectWrite. Skia does not require the additions to DirectWrite in QFE
   // 2670838, but a simple 'better than XP' check is not enough.
   if (base::win::GetVersion() < base::win::VERSION_WIN7)
     return false;
 
   base::win::OSInfo::VersionNumber os_version =
       base::win::OSInfo::GetInstance()->version_number();
   if ((os_version.major == 6) && (os_version.minor == 1)) {
@@ skipping 62 matching lines @@
       dwrite_create_factory_proc(
           DWRITE_FACTORY_TYPE_SHARED,
         __uuidof(IDWriteFactory),
         reinterpret_cast<IUnknown**>(factory.Receive()))));
   // The skia call to create a new DirectWrite font manager instance can fail
   // if we are unable to get the system font collection from the DirectWrite
   // factory. The GetSystemFontCollection method in the IDWriteFactory
   // interface fails with E_INVALIDARG on certain Windows 7 gold versions
   // (6.1.7600.*). We should just use GDI in these cases.
   SkFontMgr* direct_write_font_mgr = SkFontMgr_New_DirectWrite(factory.get());
-  if (direct_write_font_mgr) {
-    SetDefaultSkiaFactory(direct_write_font_mgr);
-    gfx::PlatformFontWin::SetDirectWriteFactory(factory.get());
-  }
+  if (!direct_write_font_mgr)
+    return;
+  dwrite_enabled = true;

[msw, 2014/12/10 23:55:50]

Why can't callers check ShouldUseDirectWrite?

[ckocagil, 2014/12/11 01:07:11]

Because some processes can choose not to initialize DirectWrite even if
ShouldUseDirectWrite is true. For example DirectWrite is always disabled in unit
tests.

[msw, 2014/12/11 23:30:12]

Okay, fair enough.

+  SetDefaultSkiaFactory(direct_write_font_mgr);
+  gfx::PlatformFontWin::SetDirectWriteFactory(factory.get());
+}
+
+bool IsDirectWriteEnabled() {
+  return dwrite_enabled;
 }
 
 }  // namespace win
 }  // namespace gfx