Viewer: Allow drag scrolling in paged mode as well

src/pyj/read_book/iframe.pyj

@@ -22,11 +22,12 @@ from read_book.extract import get_elements
 from read_book.find import reset_find_caches, select_search_result
 from read_book.flow_mode import (
     anchor_funcs as flow_anchor_funcs, auto_scroll_action as flow_auto_scroll_action,
-    cancel_drag_scroll, ensure_selection_visible, flow_onwheel,
+    cancel_drag_scroll as cancel_drag_scroll_flow, ensure_selection_visible,
-    flow_to_scroll_fraction, handle_gesture as flow_handle_gesture,
+    flow_onwheel, flow_to_scroll_fraction, handle_gesture as flow_handle_gesture,
     handle_shortcut as flow_handle_shortcut, layout as flow_layout,
     scroll_by_page as flow_scroll_by_page,
-    scroll_to_extend_annotation as flow_annotation_scroll, start_drag_scroll
+    scroll_to_extend_annotation as flow_annotation_scroll,
+    start_drag_scroll as start_drag_scroll_flow
 )
 from read_book.footnotes import is_footnote_link
 from read_book.globals import (
@@ -38,7 +39,8 @@ from read_book.mathjax import apply_mathjax
 from read_book.paged_mode import (
     anchor_funcs as paged_anchor_funcs,
     auto_scroll_action as paged_auto_scroll_action, calc_columns_per_screen,
-    current_cfi, get_columns_per_screen_data, handle_gesture as paged_handle_gesture,
+    cancel_drag_scroll as cancel_drag_scroll_paged, current_cfi,
+    get_columns_per_screen_data, handle_gesture as paged_handle_gesture,
     handle_shortcut as paged_handle_shortcut, jump_to_cfi as paged_jump_to_cfi,
     layout as paged_layout, onwheel as paged_onwheel,
     prepare_for_resize as paged_prepare_for_resize, progress_frac,
@@ -46,7 +48,7 @@ from read_book.paged_mode import (
     scroll_by_page as paged_scroll_by_page, scroll_to_elem,
     scroll_to_extend_annotation as paged_annotation_scroll,
     scroll_to_fraction as paged_scroll_to_fraction, snap_to_selection,
-    will_columns_per_screen_change
+    start_drag_scroll as start_drag_scroll_paged, will_columns_per_screen_change
 )
 from read_book.referencing import (
     elem_for_ref, end_reference_mode, start_reference_mode
@@ -75,6 +77,11 @@ def layout_style():
     return 'scrolling' if current_layout_mode() is 'flow' else 'paginated'
 
 
+def cancel_drag_scroll():
+    cancel_drag_scroll_flow()
+    cancel_drag_scroll_paged()
+
+
 class EPUBReadingSystem:
 
     @property
@@ -231,6 +238,7 @@ class IframeBoss:
             self.auto_scroll_action = flow_auto_scroll_action
             self.scroll_to_extend_annotation = flow_annotation_scroll
             self.ensure_selection_visible = ensure_selection_visible
+            self.start_drag_scroll = start_drag_scroll_flow
             paged_auto_scroll_action('stop')
         else:
             self.do_layout = paged_layout
@@ -243,6 +251,7 @@ class IframeBoss:
             self.auto_scroll_action = paged_auto_scroll_action
             self.scroll_to_extend_annotation = paged_annotation_scroll
             self.ensure_selection_visible = snap_to_selection
+            self.start_drag_scroll = start_drag_scroll_paged
             flow_auto_scroll_action('stop')
         update_settings(data.settings)
         self.keyboard_shortcut_map = create_shortcut_map(data.settings.keyboard_shortcuts)
@@ -544,7 +553,7 @@ class IframeBoss:
     def onmousemove(self, evt):
         if evt.buttons is not 1:
             return
-        if 0 <= evt.clientY <= window.innerHeight or current_layout_mode() is not 'flow':
+        if 0 <= evt.clientY <= window.innerHeight:
             cancel_drag_scroll()
             return
         sel = window.getSelection()
@@ -552,7 +561,7 @@ class IframeBoss:
             cancel_drag_scroll()
             return
         delta = evt.clientY if evt.clientY < 0 else (evt.clientY - window.innerHeight)
-        start_drag_scroll(delta)
+        self.start_drag_scroll(delta)
 
     def onmouseup(self, evt):
         cancel_drag_scroll()

src/pyj/read_book/paged_mode.pyj

@@ -746,3 +746,45 @@ def auto_scroll_action(action):
             ' scrolling'), is_non_critical=True
         )
     return False
+
+
+class DragScroller:
+
+    INTERVAL = 500
+
+    def __init__(self):
+        self.backward = False
+        self.timer_id = None
+
+    def is_running(self):
+        return self.timer_id is not None
+
+    def start(self, backward):
+        if not self.is_running() or backward is not self.backward:
+            self.stop()
+            self.backward = backward
+            self.timer_id = window.setTimeout(self.do_one_page_turn.bind(self), self.INTERVAL)
+
+    def do_one_page_turn(self):
+        pos = previous_col_location() if self.backward else next_col_location()
+        if pos >= 0:
+            scroll_to_xpos(pos)
+            self.timer_id = window.setTimeout(self.do_one_page_turn.bind(self), self.INTERVAL * 2)
+        else:
+            self.stop()
+
+    def stop(self):
+        if self.timer_id is not None:
+            window.clearTimeout(self.timer_id)
+            self.timer_id = None
+
+
+drag_scroller = DragScroller()
+
+
+def cancel_drag_scroll():
+    drag_scroller.stop()
+
+
+def start_drag_scroll(delta):
+    drag_scroller.start(delta < 0)