Ebook viewer: Use a more stable, though less accurate algorithm for calculating bookmarks. Add a --debug-javascript option. Fixes #2653 (Ebook Viewer Sometimes Has Two Scrollbars)

src/calibre/gui2/viewer/documentview.py

@@ -16,6 +16,7 @@ from calibre.gui2.viewer.config_ui import Ui_Dialog
 from calibre.gui2.viewer.js import bookmarks, referencing
 from calibre.ptempfile import PersistentTemporaryFile
 from calibre.constants import iswindows
+from calibre import prints
 
 def load_builtin_fonts():
     from calibre.ebooks.lrf.fonts.liberation import LiberationMono_BoldItalic
@@ -124,6 +125,7 @@ class Document(QWebPage):
 
     def __init__(self, *args):
         QWebPage.__init__(self, *args)
+        self.debug_javascript = False
         self.setLinkDelegationPolicy(self.DelegateAllLinks)
         self.scroll_marks = []
         pal = self.palette()
@@ -187,6 +189,20 @@ class Document(QWebPage):
             return unicode(ans.toString())
         return ans
 
+    def javaScriptConsoleMessage(self, msg, lineno, msgid):
+        if self.debug_javascript:
+            prints( 'JS:', msgid, lineno)
+            prints(msg)
+            prints(' ')
+        else:
+            return QWebPage.javaScriptConsoleMessage(self, msg, lineno, msgid)
+
+    def javaScriptAlert(self, frame, msg):
+        if self.debug_javascript:
+            prints(msg)
+        else:
+            return QWebPage.javaScriptAlert(self, frame, msg)
+
     def scroll_by(self, dx=0, dy=0):
         self.mainFrame().scroll(dx, dy)
 
@@ -272,6 +288,7 @@ class DocumentView(QWebView):
 
     def __init__(self, *args):
         QWidget.__init__(self, *args)
+        self.debug_javascript = False
         self.setSizePolicy(QSizePolicy(QSizePolicy.Expanding, QSizePolicy.Expanding))
         self._size_hint = QSize(510, 680)
         self.initial_pos = 0.0

src/calibre/gui2/viewer/js.py

@@ -1,27 +1,5 @@
 bookmarks = '''
 
-function find_enclosing_block(y) {
-    var elements = $("*", document.body);
-    var min = 0;
-    var temp, left, top, elem, width, height, ratio;
-    for (i = 0; i < elements.length; i++) {
-        elem = $(elements[i]);
-        temp = elem.offset();
-        left = temp.left; top = temp.top;
-        width = elem.width(); height = elem.height();
-        if (top > y+50) break;
-        for ( x = 40; x < window.innerWidth; x += 20) {
-            if (x >= left && x <= left+width && y >= top && y <= top+height) {
-                if (min == 0 || min.height() > height) { min = elem; break; }
-            }
-        }
-        if (min != 0 && min.height() < 200) break;
-    }
-    if (y <= 0) return document.body;
-    if (min == 0) { return find_enclosing_block(y-20); }
-    return min;
-}
-
 function selector_in_parent(elem) {
     var num = elem.prevAll().length;
     var sel = " > *:eq("+num+") ";
@@ -38,8 +16,37 @@ function selector(elem) {
     return sel;
 }
 
+function find_closest_enclosing_block(top) {
+    var START = top-1000;
+    var STOP = top;
+    var matches = [];
+    var elem, temp;
+    var width = 1000;
+
+    for (y = START; y < STOP; y += 20) {
+        for ( x = 0; x < width; x += 20) {
+            elem = document.elementFromPoint(x, y);
+            try {
+                elem = $(elem);
+                temp = elem.offset().top
+                matches.push(elem);
+                if (Math.abs(temp - START) < 25) { y = STOP; break}
+            } catch(error) {}
+        }
+    }
+
+    var miny = Math.abs(matches[0].offset().top - START), min_elem = matches[0];
+
+    for (i = 1; i < matches.length; i++) {
+        elem = matches[i];
+        temp = Math.abs(elem.offset().top - START);
+        if ( temp < miny ) { miny = temp; min_elem = elem; }
+    }
+    return min_elem;
+}
+
 function calculate_bookmark(y) {
-    var elem = find_enclosing_block(y);
+    var elem = find_closest_enclosing_block(y);
     var sel = selector(elem);
     var ratio = (y - elem.offset().top)/elem.height();
     if (ratio > 1) { ratio = 1; }

src/calibre/gui2/viewer/main.py

@@ -189,7 +189,7 @@ class HelpfulLineEdit(QLineEdit):
 
 class EbookViewer(MainWindow, Ui_EbookViewer):
 
-    def __init__(self, pathtoebook=None):
+    def __init__(self, pathtoebook=None, debug_javascript=False):
         MainWindow.__init__(self, None)
         self.setupUi(self)
         self.iterator          = None
@@ -219,6 +219,7 @@ class EbookViewer(MainWindow, Ui_EbookViewer):
         self.search.setToolTip(_('Search for text in book'))
         self.tool_bar2.insertWidget(self.action_find_next, self.search)
         self.view.set_manager(self)
+        self.view.document.debug_javascript = debug_javascript
         self.pi = ProgressIndicator(self)
         self.toc.setVisible(False)
         self.action_quit = QAction(self)
@@ -630,6 +631,8 @@ def config(defaults=None):
                      'front when started.'))
     c.add_opt('remember_window_size', default=False,
         help=_('Remember last used window size'))
+    c.add_opt('debug_javascript', ['--debug-javascript'], default=False,
+        help=_('Print javascript alert and console messages to the console'))
 
     return c
 
@@ -651,7 +654,8 @@ def main(args=sys.argv):
         app.setWindowIcon(QIcon(':/images/viewer.svg'))
         QApplication.setOrganizationName(ORG_NAME)
         QApplication.setApplicationName(APP_UID)
-        main = EbookViewer(args[1] if len(args) > 1 else None)
+        main = EbookViewer(args[1] if len(args) > 1 else None,
+                debug_javascript=opts.debug_javascript)
         sys.excepthook = main.unhandled_exception
         main.show()
         if opts.raise_window: