Android Chromium：不成功的嘗試，無法從Typeface.java類獲得C++ SkTypeface對象

標籤：chromium   skia   typeface   android jni   瀏覽器開發   

這也就是說，Java Activity層的使用者自訂預設字型通過標準framework/JNI的途徑是無法傳遞應用到Chromium核心的。

本來的基本想法是：通過Typeface.DEFAULT獲得Java層的系統當前預設字型設定，通過Java動態反射調用獲得native_instance控制代碼，然後嘗試用JNI C++代碼獲得SkTypeface*指標，調用SkTypeface::serialize序列化到一個臨時字型檔，然後將此路徑回傳Java，再重新傳到Chromium核心代碼。

帖2段核心demo代碼：

AwSettings.java:

//#if ENABLE_USER_OVERRIDES_FONTFALLBACK    //hacker techniques to get current system's default typeface and apply it to chromium/skia kernel code:    @CalledByNative    private static long getDefaultTypefaceNativePointer() {        try{            android.graphics.Typeface defaultTypeface = android.graphics.Typeface.DEFAULT;            java.lang.reflect.Field field = null;            field = android.graphics.Typeface.class.getDeclaredField("native_instance");            long ret = 0;            if (android.os.Build.VERSION.SDK_INT>=21) {                //5.0+                ret = field.getLong(defaultTypeface);            }else{                //4.4-                ret = field.getInt(defaultTypeface);//boost to long            }            Log.i(TAG, "android.graphics.Typeface.DEFAULT.native_instance="+ret);            return ret;        }catch(Exception e){            Log.e(TAG, e.getMessage(), e);            return 0;        }    }    //private boolean sUserOverridesFontFallbackEnabled = false;    private static native String nativeGetTempUserOverridesFontFallbackPath();    public void setUserOverridesFontFallbackEnabled(boolean enable) {        if (enable) {            String path = AwSettings.nativeGetTempUserOverridesFontFallbackPath();            setUserOverridesFontFallback(true, path);        }else{            setUserOverridesFontFallback(false, "");        }    } //#if

aw_settings.cc:

#if ENABLE_USER_OVERRIDES_FONTFALLBACKstatic jstring GetTempUserOverridesFontFallbackPath(JNIEnv* env, jclass clazz) {    VLOG(0)<<"GetTempUserOverridesFontFallbackPath enter";    jlong native_instance_pointer = Java_AwSettings_getDefaultTypefaceNativePointer(env);    if(native_instance_pointer==0){      VLOG(0)<<"GetTempUserOverridesFontFallbackPath getDefaultTypefaceNativePointer failed!";      return 0;    }    //SkTypeface* typeface = (SkTypeface*)(int)native_instance_pointer;    //  //ALERT: this C++ SkTypeface is got from framework layer, it may not have the same ABI compatibility with chromioum's internal skia library    TypefaceImpl* typefaceImpl = (TypefaceImpl*)native_instance_pointer;    SkTypeface* typeface = 0; //TODO: cannot get SkTypeface* from TypefaceImpl*    //i need a writable path!    FilePath cache_dir_filepath;    /*bool ret = */base::android::GetCacheDirectory(&cache_dir_filepath);    FilePath temp_filepath = cache_dir_filepath.Append( FilePath("test.ttf.ser") ); //<-- TODO: generate this    std::string gen_temp_path = temp_filepath.AsUTF8Unsafe();    const char* temp_path = gen_temp_path.c_str(); //"/data/local/test.ttf.ser";    VLOG(0)<<"GetTempUserOverridesFontFallbackPath gen_temp_path="<<temp_path;    SkFILEWStream wstream(temp_path);    typeface->serialize(&wstream);//may fail, but we don't know!    ScopedJavaLocalRef<jstring> jpath = ConvertUTF8ToJavaString(env, temp_path);    return jpath.Release();  }#endif

遺憾的是，native_instance實際上對應於不透明的TypefaceImpl*，在JNI下可能也是無法訪問的。即使能訪問，從TypefaceImpl*也得不到SkTypeface*。

Android Chromium：不成功的嘗試，無法從Typeface.java類獲得C++ SkTypeface對象