E-book viewer: Preserve the current position more accurately when changing font size/other preferences. Fixes #912406 (Preserve reading position when changing font magnification or in preferences changing font or size)

src/calibre/ebooks/oeb/display/cfi.coffee

@@ -166,6 +166,8 @@ class CanonicalFragmentIdentifier
     ###
 
     constructor: () -> # {{{
+        if not this instanceof arguments.callee
+            throw new Error('CFI constructor called as function')
         this.CREATE_RANGE_ERR = "Your browser does not support the createRange function. Update it to a newer version."
         this.IE_ERR = "Your browser is too old. You need Internet Explorer version 9 or newer."
         div = document.createElement('div')

src/calibre/gui2/viewer/documentview.py

@@ -24,6 +24,7 @@ from calibre.constants import iswindows
 from calibre import prints, guess_type
 from calibre.gui2.viewer.keys import SHORTCUTS
 from calibre.gui2.viewer.javascript import JavaScriptLoader
+from calibre.gui2.viewer.position import PagePosition
 
 # }}}
 
@@ -170,14 +171,16 @@ class Document(QWebPage): # {{{
         settings.setFontFamily(QWebSettings.SerifFont, opts.serif_family)
         settings.setFontFamily(QWebSettings.SansSerifFont, opts.sans_family)
         settings.setFontFamily(QWebSettings.FixedFont, opts.mono_family)
+        settings.setAttribute(QWebSettings.ZoomTextOnly, True)
 
     def do_config(self, parent=None):
         d = ConfigDialog(self.shortcuts, parent)
         if d.exec_() == QDialog.Accepted:
-            self.set_font_settings()
+            with self.page_position:
-            self.set_user_stylesheet()
+                self.set_font_settings()
-            self.misc_config()
+                self.set_user_stylesheet()
-            self.after_load()
+                self.misc_config()
+                self.after_load()
 
     def __init__(self, shortcuts, parent=None, resize_callback=lambda: None,
             debug_javascript=False):
@@ -196,6 +199,7 @@ class Document(QWebPage): # {{{
         pal = self.palette()
         pal.setBrush(QPalette.Background, QColor(0xee, 0xee, 0xee))
         self.setPalette(pal)
+        self.page_position = PagePosition(self)
 
         settings = self.settings()
 
@@ -895,23 +899,25 @@ class DocumentView(QWebView): # {{{
     @dynamic_property
     def multiplier(self):
         def fget(self):
-            return self.document.mainFrame().textSizeMultiplier()
+            return self.zoomFactor()
         def fset(self, val):
-            self.document.mainFrame().setTextSizeMultiplier(val)
+            self.setZoomFactor(val)
             self.magnification_changed.emit(val)
         return property(fget=fget, fset=fset)
 
     def magnify_fonts(self, amount=None):
         if amount is None:
             amount = self.document.font_magnification_step
-        self.multiplier += amount
+        with self.document.page_position:
+            self.multiplier += amount
         return self.document.scroll_fraction
 
     def shrink_fonts(self, amount=None):
         if amount is None:
             amount = self.document.font_magnification_step
         if self.multiplier >= amount:
-            self.multiplier -= amount
+            with self.document.page_position:
+                self.multiplier -= amount
         return self.document.scroll_fraction
 
     def changeEvent(self, event):

src/calibre/gui2/viewer/main.py

@@ -481,16 +481,14 @@ class EbookViewer(MainWindow, Ui_EbookViewer):
         self.load_ebook(action.path)
 
     def font_size_larger(self):
-        frac = self.view.magnify_fonts()
+        self.view.magnify_fonts()
         self.action_font_size_larger.setEnabled(self.view.multiplier < 3)
         self.action_font_size_smaller.setEnabled(self.view.multiplier > 0.2)
-        self.set_page_number(frac)
 
     def font_size_smaller(self):
-        frac = self.view.shrink_fonts()
+        self.view.shrink_fonts()
         self.action_font_size_larger.setEnabled(self.view.multiplier < 3)
         self.action_font_size_smaller.setEnabled(self.view.multiplier > 0.2)
-        self.set_page_number(frac)
 
     def magnification_changed(self, val):
         tt = _('Make font size %(which)s\nCurrent magnification: %(mag).1f')

src/calibre/gui2/viewer/position.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python
+# vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+from __future__ import (unicode_literals, division, absolute_import,
+                        print_function)
+
+__license__   = 'GPL v3'
+__copyright__ = '2012, Kovid Goyal <kovid@kovidgoyal.net>'
+__docformat__ = 'restructuredtext en'
+
+import json
+
+class PagePosition(object):
+
+    def __init__(self, document):
+        self.document = document
+
+    @property
+    def viewport_cfi(self):
+        ans = None
+        res = self.document.mainFrame().evaluateJavaScript('''
+            ans = 'undefined';
+            try {
+                ans = window.cfi.at_current();
+                if (!ans) ans = 'undefined';
+            } catch (err) {
+                window.console.log(err);
+            }
+            window.console.log("Viewport cfi: " + ans);
+            ans;
+        ''')
+        if res.isValid() and not res.isNull() and res.type() == res.String:
+            c = unicode(res.toString())
+            if c != 'undefined':
+                ans = c
+        return ans
+
+    def scroll_to_cfi(self, cfi):
+        if cfi:
+            cfi = json.dumps(cfi)
+            self.document.mainFrame().evaluateJavaScript('''
+                    window.cfi.scroll_to(%s);
+                '''%cfi)
+
+    @property
+    def current_pos(self):
+        ans = self.viewport_cfi
+        if not ans:
+            ans = self.document.scroll_fraction
+        return ans
+
+    def __enter__(self):
+        self._cpos = self.current_pos
+
+    def __exit__(self, *args):
+        if isinstance(self._cpos, (int, float)):
+            self.document.scroll_fraction = self._cpos
+        else:
+            self.scroll_to_cfi(self._cpos)
+        self._cpos = None
+