Add option to specify font fallback when creating the skia font manager

src/ports/SkFontMgr_win_dw.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkTypes.h"
 #if defined(SK_BUILD_FOR_WIN32)
 
@@ skipping 246 matching lines @@
     *fontFileEnumerator = enumerator.release();
     return S_OK;
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 
 class SkFontMgr_DirectWrite : public SkFontMgr {
 public:
     /** localeNameLength must include the null terminator. */
     SkFontMgr_DirectWrite(IDWriteFactory* factory, IDWriteFontCollection* fontCollection,
-                          WCHAR* localeName, int localeNameLength)
+                          IDWriteFontFallback* fallback, WCHAR* localeName, int localeNameLength)
         : fFactory(SkRefComPtr(factory))
+#if SK_HAS_DWRITE_2_H
+        , fFontFallback(SkSafeRefComPtr(fallback))
+#endif
         , fFontCollection(SkRefComPtr(fontCollection))
         , fLocaleName(localeNameLength)
     {
 #if SK_HAS_DWRITE_2_H
         if (!SUCCEEDED(fFactory->QueryInterface(&fFactory2))) {
             // IUnknown::QueryInterface states that if it fails, punk will be set to nullptr.
             // http://blogs.msdn.com/b/oldnewthing/archive/2004/03/26/96777.aspx
             SkASSERT_RELEASE(nullptr == fFactory2.get());
         }
+        if (fFontFallback.get()) {
+          SkASSERT(fFactory2.get());

[bungeman-skia, 2016/04/14 21:48:39]

nit: Skia uses 4 space indents.

[Ilya Kulshin, 2016/04/14 22:30:37]

Done.

+        }
 #endif
         memcpy(fLocaleName.get(), localeName, localeNameLength * sizeof(WCHAR));
     }
 
 protected:
     int onCountFamilies() const override;
     void onGetFamilyName(int index, SkString* familyName) const override;
     SkFontStyleSet* onCreateStyleSet(int index) const override;
     SkFontStyleSet* onMatchFamily(const char familyName[]) const override;
     virtual SkTypeface* onMatchFamilyStyle(const char familyName[],
@@ skipping 14 matching lines @@
     HRESULT getDefaultFontFamily(IDWriteFontFamily** fontFamily) const;
 
     /** Creates a typeface using a typeface cache. */
     SkTypeface* createTypefaceFromDWriteFont(IDWriteFontFace* fontFace,
                                              IDWriteFont* font,
                                              IDWriteFontFamily* fontFamily) const;
 
     SkTScopedComPtr<IDWriteFactory> fFactory;
 #if SK_HAS_DWRITE_2_H
     SkTScopedComPtr<IDWriteFactory2> fFactory2;
+    SkTScopedComPtr<IDWriteFontFallback> fFontFallback;
 #endif
     SkTScopedComPtr<IDWriteFontCollection> fFontCollection;
     SkSMallocWCHAR fLocaleName;
     mutable SkMutex fTFCacheMutex;
     mutable SkTypefaceCache fTFCache;
 
     friend class SkFontStyleSet_DirectWrite;
     friend class FontFallbackRenderer;
 };
 
@@ skipping 434 matching lines @@
     } else {
         // TODO: support fallback stack.
         // TODO: DirectWrite supports 'zh-CN' or 'zh-Hans', but 'zh' misses completely
         // and may produce a Japanese font.
         HRN(sk_cstring_to_wchar(bcp47[bcp47Count - 1], &dwBcp47Local));
         dwBcp47 = &dwBcp47Local;
     }
 
 #if SK_HAS_DWRITE_2_H
     if (fFactory2.get()) {
-        SkTScopedComPtr<IDWriteFontFallback> fontFallback;
-        HRNM(fFactory2->GetSystemFontFallback(&fontFallback), "Could not get system fallback.");
+        SkTScopedComPtr<IDWriteFontFallback> systemFontFallback;
+        IDWriteFontFallback* fontFallback = fFontFallback.get();
+        if (!fontFallback) {
+            HRNM(fFactory2->GetSystemFontFallback(&systemFontFallback),
+                 "Could not get system fallback.");
+            fontFallback = systemFontFallback.get();
+        }

[bungeman-skia, 2016/04/14 21:48:39]

Hmmm... I see. The idea is that while making the transition we aren't using this
anyway, so get the default here if needed. If we tried to get the default in
SkFontMgr_New_DirectWrite then we'd end up trying to get one, which we don't
want.

So after Chromium provides an IDWriteFontFallback to SkFontMgr_New_DirectWrite,
this default code could be moved out to the constructor (since Chromium would no
longer be going down the path which would create the default).

[Ilya Kulshin, 2016/04/14 22:30:37]

Yes, after Chromium starts providing the fallback, Chromium wouldn't end up in
this block. However I'm not sure about other users of Skia. We've seen in
Chromium that creating the fallback is potentially expensive, so I'm somewhat
reluctant to create it automatically in the constructor if it might not even be
needed.

 
         SkTScopedComPtr<IDWriteNumberSubstitution> numberSubstitution;
         HRNM(fFactory2->CreateNumberSubstitution(DWRITE_NUMBER_SUBSTITUTION_METHOD_NONE, nullptr, TRUE,
                                                  &numberSubstitution),
              "Could not create number substitution.");
         SkTScopedComPtr<FontFallbackSource> fontFallbackSource(
             new FontFallbackSource(str, strLen, *dwBcp47, numberSubstitution.get()));
 
         UINT32 mappedLength;
         SkTScopedComPtr<IDWriteFont> font;
@@ skipping 284 matching lines @@
 
     return fFontMgr->createTypefaceFromDWriteFont(fontFace.get(), font.get(),
                                                   fFontFamily.get());
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 #include "SkTypeface_win.h"
 
 SK_API SkFontMgr* SkFontMgr_New_DirectWrite(IDWriteFactory* factory,
                                             IDWriteFontCollection* collection) {
+    return SkFontMgr_New_DirectWrite(factory, collection, nullptr);
+}
+
+SK_API SkFontMgr* SkFontMgr_New_DirectWrite(IDWriteFactory* factory,
+                                            IDWriteFontCollection* collection,
+                                            IDWriteFontFallback* fallback) {
     if (nullptr == factory) {
         factory = sk_get_dwrite_factory();
         if (nullptr == factory) {
             return nullptr;
         }
     }
 
     SkTScopedComPtr<IDWriteFontCollection> systemFontCollection;
     if (nullptr == collection) {
         HRNM(factory->GetSystemFontCollection(&systemFontCollection, FALSE),
@@ skipping 10 matching lines @@
     HRESULT hr = SkGetGetUserDefaultLocaleNameProc(&getUserDefaultLocaleNameProc);
     if (nullptr == getUserDefaultLocaleNameProc) {
         SK_TRACEHR(hr, "Could not get GetUserDefaultLocaleName.");
     } else {
         localeNameLen = getUserDefaultLocaleNameProc(localeNameStorage, LOCALE_NAME_MAX_LENGTH);
         if (localeNameLen) {
             localeName = localeNameStorage;
         };
     }
 
-    return new SkFontMgr_DirectWrite(factory, collection, localeName, localeNameLen);
+    return new SkFontMgr_DirectWrite(factory, collection, fallback, localeName, localeNameLen);
 }
 
 #include "SkFontMgr_indirect.h"
 SK_API SkFontMgr* SkFontMgr_New_DirectWriteRenderer(SkRemotableFontMgr* proxy) {
     SkAutoTUnref<SkFontMgr> impl(SkFontMgr_New_DirectWrite());
     if (impl.get() == nullptr) {
         return nullptr;
     }
     return new SkFontMgr_Indirect(impl.get(), proxy);
 }
 #endif//defined(SK_BUILD_FOR_WIN32)