Make extending the selection on scroll more robust

src/pyj/read_book/create_annotation.pyj

@@ -378,6 +378,15 @@ class CreateAnnotation:
                 self.place_handles(msg.extents)
         elif msg.type is 'update-handles':
             self.place_handles(msg.extents)
+            if msg.from_scroll and not msg.selection_extended:
+                middle = map_from_iframe_coords({
+                    'x': msg.page_rect.left + msg.page_rect.width // 2,
+                    'y': msg.page_rect.top + msg.page_rect.height // 2
+                })
+                handle = self.left_handle if msg.backwards else self.right_handle
+                handle.style.display = 'block'
+                handle.style.left = f'{middle.x}px'
+                handle.style.top = f'{middle.y}px'
         elif msg.type is 'highlight-applied':
             if not msg.ok:
                 return error_dialog(

src/pyj/read_book/iframe.pyj

@@ -31,11 +31,11 @@ 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,
-    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,
-    reset_paged_mode_globals, resize_done as paged_resize_done,
+    current_cfi, current_page_width, 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, reset_paged_mode_globals, resize_done as paged_resize_done,
     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,
@@ -634,8 +634,12 @@ class IframeBoss:
                 extents=selection_extents_at_point(data.x, data.y, in_flow_mode))
         elif data.type is 'scroll':
             if self.scroll_to_extend_annotation(data.backwards):
-                extend_selection_after_scroll(data.backwards, in_flow_mode)
-                self.send_message('annotations', type='update-handles', extents=selection_extents(in_flow_mode))
+                page_rect = {'width': current_page_width()}
+                extended = extend_selection_after_scroll(data.backwards, in_flow_mode, page_rect)
+                self.send_message(
+                    'annotations', type='update-handles', extents=selection_extents(in_flow_mode),
+                    backwards=data.backwards, from_scroll=True, selection_extended=extended, page_rect=page_rect
+                )
         elif data.type is 'perp-scroll':
             if in_flow_mode and flow_annotation_scroll(data.backwards, True):
                 self.send_message('annotations', type='update-handles', extents=selection_extents(in_flow_mode))

src/pyj/read_book/paged_mode.pyj

@@ -164,6 +164,10 @@ def will_columns_per_screen_change():
     return calc_columns_per_screen() != cols_per_screen
 
 
+def current_page_width():
+    return col_width
+
+
 def layout(is_single_page, on_resize):
     nonlocal _in_paged_mode, col_width, col_and_gap, screen_height, gap, screen_width, is_full_screen_layout, cols_per_screen, number_of_cols
     body_style = window.getComputedStyle(document.body)

src/pyj/select.pyj

@@ -98,37 +98,53 @@ def selection_extents_at_point(x, y, in_flow_mode):
     return ans
 
 
-def extend_selection_after_scroll(backwards, in_flow_mode):
+def extend_selection_after_scroll(backwards, in_flow_mode, page_rect):
+    page_rect.top = page_rect.left = 0
+    page_rect.bottom = window.innerHeight
+    page_rect.right = page_rect.width
+    if not in_flow_mode and not backwards:
+        page_rect.right = window.innerWidth
+        page_rect.left = window.innerWidth - page_rect.width
+    page_rect.width = page_rect.right - page_rect.left
+    page_rect.height = page_rect.bottom - page_rect.top
+
     sel = window.getSelection()
     if not sel.rangeCount:
-        return
+        return False
+    if in_flow_mode:
+        page_rect.width = window.innerWidth
     r = sel.getRangeAt(0)
     q = r.cloneRange()
     q.collapse(backwards)
-    rects = r.getClientRects()
+    rects = q.getClientRects()
     if not rects.length:
-        return
+        return False
     rect = rects[0]
+
+    in_page_already = rect.left >= page_rect.left and rect.top >= page_rect.top and rect.bottom <= page_rect.bottom and rect.right <= page_rect.right
+    if in_page_already:
+        return True
+    dx = page_rect.width // 10
+    dy = page_rect.height // 10
+    middle_x = page_rect.left + page_rect.width // 2
+    for yi in range(1, 10):
         if backwards:
-        if in_flow_mode and rect.bottom <= window.innerHeight:
-            return
-        if not in_flow_mode and rect.right <= window.innerWidth:
-            return
+            y = page_rect.bottom - dy * yi
         else:
-        if in_flow_mode and rect.top >= 0:
-            return
-        if not in_flow_mode and rect.left >= 0:
-            return
-    x = window.innerWidth // 2
-    y = window.innerHeight // 3
-    if backwards:
-        y *= 2
+            y = page_rect.top + dy * yi
+        for xi in range(4):
+            xvals = v'[-1, 1]' if xi else v'[1]'
+            for xw in xvals:
+                x = middle_x + xw * dx
                 p = range_from_point(x, y)
                 if p:
                     if backwards:
                         r.setStart(p.startContainer, p.startOffset)
                     else:
                         r.setEnd(p.startContainer, p.startOffset)
+                    return True
+    # could not find any content on page
+    return False
 
 
 def set_selections_extents_to(extents):