E-book viewer: When hovering over the top/bottom margin show a button indicating that a click will open the viewer controls. Fixes #2064665 [[Enhancement] More Intuitive EPUB Reader Menu Access](https://bugs.launchpad.net/calibre/+bug/2064665)

src/pyj/read_book/prefs/head_foot.pyj

@@ -3,12 +3,13 @@
 from __python__ import bound_methods, hash_literals
 
 from elementmaker import E
-from gettext import gettext as _, ngettext
+from gettext import gettext as _
+from gettext import ngettext
 
 from book_list.globals import get_session_data
-from dom import unique_id
+from dom import clear, unique_id
 from read_book.prefs.utils import create_button_box
-from session import session_defaults, get_interface_data
+from session import get_interface_data, session_defaults
 from utils import fmt_sidx
 
 CONTAINER = unique_id('reader-hf-prefs')
@@ -38,6 +39,7 @@ def create_item(region, label, style):
             opt(_('View mode as icon'), 'view-mode-icon'),
             sep(),
             opt(_('Clock'), 'clock'),
+            opt(_('Controls button on hover'), 'menu-icon-on-hover'),
             sep(),
             opt(_('Progress'), 'progress'),
             opt(_('Time to read book'), 'time-book'),
@@ -189,6 +191,10 @@ def render_head_foot(div, which, region, metadata, current_toc_node, current_toc
     has_clock = False
     if override:
         text = override
+    elif field is 'menu-icon-on-hover':
+        clear(div)
+        div.appendChild(E.div(class_='visible-on-hover', E.span(_('Show controls')), title=_('Show viewer controls'), style='cursor: pointer'))
+        return has_clock
     elif field is 'progress':
         percent = min(100, max(Math.round(pos.progress_frac * 100), 0))
         text = percent + '%'

src/pyj/read_book/view.pyj

@@ -60,6 +60,9 @@ add_extra_css(def():
     ans += build_rule(sel + ':active > .not-arrow', display='none')
     ans += build_rule(sel + ':hover > .arrow', display='block')
     ans += build_rule(sel + ':active > .arrow', display='block', transform='scale(2)')
+    ans += build_rule('.book-h-margin .visible-on-hover', visibility='hidden')
+    ans += build_rule('.book-h-margin:hover .visible-on-hover', visibility='visible')
+    ans += build_rule('.book-h-margin .visible-on-hover:hover', color=get_color('window-hover-foreground'))
     return ans
 )
 
@@ -180,7 +183,7 @@ def margin_elem(sd, which, id, onclick, oncontextmenu):
     fsz = header_footer_font_size(sz)
     s = '; text-overflow: ellipsis; white-space: nowrap; overflow: hidden'
     ans = E.div(
-        style=f'height:{sz}px; overflow: hidden; font-size:{fsz}px; width:100%; padding: 0; display: flex; justify-content: space-between; align-items: center; user-select: none',
+        style=f'height:{sz}px; overflow: hidden; font-size:{fsz}px; width:100%; padding: 0; display: flex; justify-content: space-between; align-items: center; user-select: none; cursor: pointer', class_='book-h-margin',
         id=id,
         E.div(style='margin-right: 1.5em' + s), E.div(style=s), E.div(style='margin-left: 1.5em' + s)
     )
@@ -406,7 +409,7 @@ class View:
             self.focus_iframe()
 
     def bottom_margin_clicked(self, event):
-        if event.button is 2:
+        if event.button is 0 or event.button is 2:
             event.preventDefault(), event.stopPropagation()
             window.setTimeout(self.show_chrome, 0)
         self.focus_iframe()

src/pyj/session.pyj

@@ -33,8 +33,8 @@ all_settings = {
     'controls_help_shown_count_rtl_page_progression': {'default': 0, 'category': 'read_book', 'is_local': True, 'disallowed_in_profile': True},
     'cover_preserve_aspect_ratio': {'default': True, 'category': 'read_book'},
     'current_color_scheme': {'default': 'system', 'category': 'read_book'},
-    'footer': {'default': {'right': 'progress'}, 'category': 'read_book'},
-    'header': {'default': {}, 'category': 'read_book'},
+    'footer': {'default': {'left': 'menu-icon-on-hover', 'right': 'progress'}, 'category': 'read_book'},
+    'header': {'default': {'right': 'menu-icon-on-hover'}, 'category': 'read_book'},
     'controls_footer': {'default': {'right': 'progress'}, 'category': 'read_book'},
     'left-margin': {'default': {}, 'category': 'read_book'},
     'right-margin': {'default': {}, 'category': 'read_book'},