Viewer: Add options to control scrolling using the mouse in paged mode.

Fixes #1846800 [Feature request: Add an option for mouse scroll to scroll by screen fulls rather than a single page](https://bugs.launchpad.net/calibre/+bug/1846800)

src/pyj/read_book/iframe.pyj

@@ -197,7 +197,7 @@ class IframeBoss:
         if current_layout_mode() is 'flow':
             flow_scroll_by_page(backwards)
         else:
-            paged_scroll_by_page(backwards, True)
+            paged_scroll_by_page(backwards, data.all_pages_on_screen)
 
     def change_font_size(self, data):
         if data.base_font_size? and data.base_font_size != opts.base_font_size:

src/pyj/read_book/paged_mode.pyj

@@ -446,6 +446,9 @@ def progress_frac(frac):
 def onwheel(evt):
     if evt.deltaY:
         backward = evt.deltaY < 0
+        if opts.paged_wheel_scrolls_by_screen:
+            x = previous_screen_location() if backward else next_screen_location()
+        else:
             x = previous_col_location() if backward else next_col_location()
         if x is -1:
             get_boss().send_message('next_spine_item', previous=backward)

src/pyj/read_book/prefs/main.pyj

@@ -12,6 +12,7 @@ from read_book.prefs.colors import commit_colors, create_colors_panel
 from read_book.prefs.fonts import commit_fonts, create_fonts_panel
 from read_book.prefs.head_foot import commit_head_foot, create_head_foot_panel
 from read_book.prefs.keyboard import commit_keyboard, create_keyboard_panel
+from read_book.prefs.scrolling import commit_scrolling, create_scrolling_panel
 from read_book.prefs.layout import commit_layout, create_layout_panel
 from read_book.prefs.misc import commit_misc, create_misc_panel
 from read_book.prefs.user_stylesheet import (
@@ -71,6 +72,7 @@ class Prefs:
             create_item(_('Page layout'), def():self.show_panel('layout');, _('Page margins and number of pages per screen')),
             create_item(_('Styles'), def():self.show_panel('user_stylesheet');, _('Style rules for text and background image')),
             create_item(_('Headers and footers'), def():self.show_panel('head_foot');, _('Customize the headers and footers')),
+            create_item(_('Scrolling behavior'), def():self.show_panel('scrolling');, _('Control how the viewer scrolls')),
             create_item(_('Keyboard shortcuts'), def():self.show_panel('keyboard');, _('Customize the keyboard shortcuts')),
         ]
         if runtime.is_standalone_viewer:
@@ -129,6 +131,13 @@ class Prefs:
     def close_keyboard(self):
         commit_keyboard(self.onchange, self.container)
 
+    def display_scrolling(self, container):
+        document.getElementById(self.title_id).textContent = _('Scrolling behavior')
+        create_scrolling_panel(container, self.onclose)
+
+    def close_scrolling(self):
+        commit_scrolling(self.onchange, self.container)
+
 
 def create_prefs_panel(container, close_func, on_change):
     Prefs(container, close_func, on_change)

src/pyj/read_book/prefs/scrolling.pyj

@@ -0,0 +1,59 @@
+# vim:fileencoding=utf-8
+# License: GPL v3 Copyright: 2016, Kovid Goyal <kovid at kovidgoyal.net>
+from __python__ import bound_methods, hash_literals
+
+from elementmaker import E
+from gettext import gettext as _
+
+from book_list.globals import get_session_data
+from dom import unique_id
+from widgets import create_button
+from session import defaults
+
+CONTAINER = unique_id('standalone-scrolling-settings')
+
+
+def restore_defaults():
+    container = get_container()
+    for control in container.querySelectorAll('input[name]'):
+        control.checked = defaults[control.getAttribute('name')]
+
+
+def get_container():
+    return document.getElementById(CONTAINER)
+
+
+def create_scrolling_panel(container):
+    container.appendChild(E.div(id=CONTAINER, style='margin: 1rem'))
+    container = container.lastChild
+    sd = get_session_data()
+
+    def cb(name, text):
+        ans = E.input(type='checkbox', name=name)
+        if sd.get(name):
+            ans.checked = True
+        return E.div(style='margin-top:1ex', E.label(ans, '\xa0' + text))
+
+    container.appendChild(E.div(style='margin-top:1ex', _(
+        'Control how mouse based scrolling works in paged mode')))
+    container.appendChild(cb(
+        'paged_wheel_scrolls_by_screen', _('Mouse wheel scrolls by screen fulls instead of pages')))
+    container.appendChild(cb(
+        'paged_margin_clicks_scroll_by_screen', _('Clicking on the margins scrolls by screen fulls instead of pages')))
+
+    container.appendChild(E.div(
+        style='margin-top: 1rem', create_button(_('Restore defaults'), action=restore_defaults)
+    ))
+
+
+develop = create_scrolling_panel
+
+
+def commit_scrolling(onchange):
+    sd = get_session_data()
+    container = get_container()
+    for control in container.querySelectorAll('input[name]'):
+        name = control.getAttribute('name')
+        val = control.checked
+        sd.set(name, None if val is defaults[name] else val)
+    onchange()

src/pyj/read_book/settings.pyj

@@ -16,8 +16,9 @@ def update_settings(settings):
     opts.base_font_size = max(8, min(settings.base_font_size or 16, 64))
     opts.user_stylesheet = settings.user_stylesheet or ''
     opts.hide_tooltips = settings.hide_tooltips
-    opts.cover_preserve_aspect_ratio = settings.cover_preserve_aspect_ratio
+    opts.cover_preserve_aspect_ratio = v'!!settings.cover_preserve_aspect_ratio'
     opts.bg_image_fade = settings.bg_image_fade or 'transparent'
+    opts.paged_wheel_scrolls_by_screen = v'!!settings.paged_wheel_scrolls_by_screen'
 
 update_settings()
 

src/pyj/read_book/view.pyj

@@ -225,12 +225,14 @@ class View:
     def left_margin_clicked(self, event):
         if event.button is 0:
             event.preventDefault(), event.stopPropagation()
-            self.iframe_wrapper.send_message('next_screen', backwards=True)
+            sd = get_session_data()
+            self.iframe_wrapper.send_message('next_screen', backwards=True, all_pages_on_screen=sd.get('paged_margin_clicks_scroll_by_screen'))
 
     def right_margin_clicked(self, event):
         if event.button is 0:
             event.preventDefault(), event.stopPropagation()
-            self.iframe_wrapper.send_message('next_screen', backwards=False)
+            sd = get_session_data()
+            self.iframe_wrapper.send_message('next_screen', backwards=False, all_pages_on_screen=sd.get('paged_margin_clicks_scroll_by_screen'))
 
     def top_margin_clicked(self, event):
         if event.button is 0:
@@ -584,6 +586,7 @@ class View:
             'keyboard_shortcuts': sd.get('keyboard_shortcuts'),
             'hide_tooltips': sd.get('hide_tooltips'),
             'cover_preserve_aspect_ratio': sd.get('cover_preserve_aspect_ratio'),
+            'paged_wheel_scrolls_by_screen': sd.get('paged_wheel_scrolls_by_screen'),
         }
 
     def show_name(self, name, initial_position=None):

src/pyj/session.pyj

@@ -49,6 +49,8 @@ defaults = {
     'standalone_font_settings': {},
     'standalone_misc_settings': {},
     'standalone_recently_opened': v'[]',
+    'paged_wheel_scrolls_by_screen': False,
+    'paged_margin_clicks_scroll_by_screen': True,
 }
 
 is_local_setting = {