Fix embedded fonts not working in preview panel

Add the embedded fonts to Qt and prevent web kit from loading them to
workaround the bug in qt webkit.

src/calibre/gui2/tweak_book/boss.py

@@ -28,7 +28,7 @@ from calibre.gui2.tweak_book import set_current_container, current_container, tp
 from calibre.gui2.tweak_book.undo import GlobalUndoHistory
 from calibre.gui2.tweak_book.file_list import NewFileDialog
 from calibre.gui2.tweak_book.save import SaveManager
-from calibre.gui2.tweak_book.preview import parse_worker
+from calibre.gui2.tweak_book.preview import parse_worker, font_cache
 from calibre.gui2.tweak_book.toc import TOCEditor
 from calibre.gui2.tweak_book.editor import editor_from_syntax, syntax_from_mime
 
@@ -114,6 +114,7 @@ class Boss(QObject):
         parse_worker.clear()
         container = job.result
         set_current_container(container)
+        font_cache.remove_fonts()
         self.current_metadata = self.gui.current_metadata = container.mi
         self.global_undo.open_book(container)
         self.gui.update_window_title()

src/calibre/gui2/tweak_book/preview.py

@@ -12,15 +12,17 @@ from base64 import b64encode
 from future_builtins import map
 from threading import Thread
 from Queue import Queue, Empty
+from collections import namedtuple
 
 from PyQt4.Qt import (
     QWidget, QVBoxLayout, QApplication, QSize, QNetworkAccessManager, QMenu, QIcon,
     QNetworkReply, QTimer, QNetworkRequest, QUrl, Qt, QNetworkDiskCache, QToolBar,
-    pyqtSlot, pyqtSignal)
+    pyqtSlot, pyqtSignal, QFontDatabase)
 from PyQt4.QtWebKit import QWebView, QWebInspector, QWebPage
 
 from calibre import prints
 from calibre.constants import iswindows
+from calibre.ebooks.oeb.polish.container import OEB_FONTS
 from calibre.ebooks.oeb.polish.parsing import parse
 from calibre.ebooks.oeb.base import serialize, OEB_DOCS
 from calibre.ptempfile import PersistentTemporaryDirectory
@@ -38,6 +40,31 @@ def get_data(name):
         return editors[name].get_raw_data()
     return current_container().raw_data(name)
 
+class FontCache(object):
+
+    def __init__(self):
+        self.cache = {}
+        self.entry = namedtuple('Entry', 'size hash families')
+
+    def remove_fonts(self):
+        for font_id in self.cache:
+            QFontDatabase.removeApplicationFont(font_id)
+        self.cache.clear()
+
+    def add_font(self, data):
+        existing = None
+        for font_id, entry in self.cache.iteritems():
+            if entry.size == len(data) and entry.hash == hash(data):
+                existing = entry
+                break
+        if existing is None:
+            font_id = QFontDatabase.addApplicationFontFromData(data)
+            if font_id > -1:
+                families = frozenset(map(lambda x:icu_lower(unicode(x)), QFontDatabase.applicationFontFamilies(font_id)))
+                self.cache[font_id] = self.entry(len(data), hash(data), families)
+
+font_cache = FontCache()
+
 # Parsing of html to add linenumbers {{{
 def parse_html(raw):
     root = parse(raw, decoder=lambda x:x.decode('utf-8'), line_numbers=True, linenumber_attribute='data-lnum')
@@ -149,6 +176,12 @@ class NetworkReply(QNetworkReply):
             self.setHeader(QNetworkRequest.ContentTypeHeader, mime_type)
             self.setHeader(QNetworkRequest.ContentLengthHeader, len(self.__data))
             QTimer.singleShot(0, self.finalize_reply)
+            if mime_type in OEB_FONTS:
+                font_cache.add_font(data)
+                # We prevent the use of the embedded font because of the the
+                # bug in Qt WebKit,
+                # https://bugs.webkit.org/show_bug.cgi?id=29433
+                self.__data = b''
 
     def check_for_parse(self):
         if self._aborted: