Re-organize code to get anchor visibility

src/pyj/read_book/anchor_visibility.pyj

@@ -0,0 +1,40 @@
+# vim:fileencoding=utf-8
+# License: GPL v3 Copyright: 2023, Kovid Goyal <kovid at kovidgoyal.net>
+from __python__ import bound_methods, hash_literals
+
+from read_book.globals import current_layout_mode, get_boss
+from read_book.viewport import scroll_viewport
+
+anchor_position_cache = {}
+
+def invalidate_anchor_position_cache():
+    nonlocal anchor_position_cache
+    anchor_position_cache = {
+        'layout_mode': current_layout_mode(), 'width': scroll_viewport.width(), 'height': scroll_viewport.height(),
+        'positions': v'{}',
+    }
+
+
+def ensure_anchor_cache_valid():
+    a = anchor_position_cache
+    if a.layout_mode is not current_layout_mode() or a.width is not scroll_viewport.width() or a.height is not scroll_viewport.height():
+        invalidate_anchor_position_cache()
+
+
+def position_for_anchor(anchor):
+    ensure_anchor_cache_valid()
+    cache = anchor_position_cache.positions
+    val = cache[anchor]
+    if val?:
+        return val
+    anchor_funcs = get_boss().anchor_funcs
+    elem = document.getElementById(anchor)
+    val = anchor_funcs.pos_for_elem(elem) if elem else anchor_funcs.pos_for_elem()
+    cache[anchor] = val
+    return val
+
+
+def is_anchor_on_screen(anchor):
+    pos = position_for_anchor(anchor)
+    anchor_funcs = get_boss().anchor_funcs
+    return anchor_funcs.visibility(pos) is 0

src/pyj/read_book/iframe.pyj

@@ -9,6 +9,7 @@ from range_utils import (
     all_annots_in_selection, highlight_associated_with_selection, last_span_for_crw,
     reset_highlight_counter, select_crw, unwrap_all_crw, unwrap_crw, wrap_text_in_range
 )
+from read_book.anchor_visibility import invalidate_anchor_position_cache
 from read_book.cfi import cfi_for_selection, range_from_cfi
 from read_book.extract import get_elements
 from read_book.find import (
@@ -402,6 +403,7 @@ class IframeBoss:
                 if cfi:
                     self.jump_to_cfi('/' + cfi)
             self.update_cfi()
+        invalidate_anchor_position_cache()
         self.update_toc_position(True)
 
     def number_of_columns_changed(self, data):
@@ -435,6 +437,7 @@ class IframeBoss:
             self.apply_highlights_on_load(self.highlights_to_apply)
             self.highlights_to_apply = None
         apply_settings()
+        invalidate_anchor_position_cache()
         fix_fullscreen_svg_images()
         self.do_layout(self.is_titlepage)
         if self.mathjax:
@@ -549,7 +552,7 @@ class IframeBoss:
                         'update_progress_frac', progress_frac=pf, file_progress_frac=fpf, page_counts=page_counts())
 
     def update_toc_position(self, recalculate_toc_anchor_positions):
-        visible_anchors = update_visible_toc_anchors(self.book.manifest.toc_anchor_map, self.anchor_funcs, bool(recalculate_toc_anchor_positions))
+        visible_anchors = update_visible_toc_anchors(self.book.manifest.toc_anchor_map, bool(recalculate_toc_anchor_positions))
         self.send_message('update_toc_position', visible_anchors=visible_anchors)
 
     def onscroll(self):
@@ -815,7 +818,7 @@ class IframeBoss:
         sel = window.getSelection()
         if not sel.rangeCount:
             return
-        anchor_before = find_anchor_before_range(sel.getRangeAt(0), self.book.manifest.toc_anchor_map, self.anchor_funcs)
+        anchor_before = find_anchor_before_range(sel.getRangeAt(0), self.book.manifest.toc_anchor_map)
         text = sel.toString()
         bounds = cfi_for_selection()
         style = highlight_style_as_css(style, opts.is_dark_theme, opts.color_scheme.foreground)

src/pyj/read_book/toc.pyj

@@ -2,14 +2,19 @@
 # License: GPL v3 Copyright: 2016, Kovid Goyal <kovid at kovidgoyal.net>
 from __python__ import hash_literals
 
-from complete import create_search_bar
-from dom import set_css, svgicon, ensure_id
 from elementmaker import E
+
+from complete import create_search_bar
+from dom import ensure_id, set_css, svgicon
 from gettext import gettext as _
 from modals import error_dialog
-from widgets import create_tree, find_text_in_tree, scroll_tree_item_into_view
-from read_book.globals import toc_anchor_map, set_toc_anchor_map, current_spine_item, current_layout_mode, current_book
+from read_book.anchor_visibility import position_for_anchor
+from read_book.globals import (
+    current_book, current_layout_mode, current_spine_item, get_boss, set_toc_anchor_map,
+    toc_anchor_map
+)
 from read_book.viewport import scroll_viewport
+from widgets import create_tree, find_text_in_tree, scroll_tree_item_into_view
 
 
 def update_visible_toc_nodes(visible_anchors):
@@ -198,20 +203,16 @@ def create_toc_panel(book, container, onclick):
     toc_panel.style.flexShrink = '1'
     toc_panel.style.overflow = 'auto'
 
-def recalculate_toc_anchor_positions(tam, anchor_funcs):
+def recalculate_toc_anchor_positions(tam):
     name = current_spine_item().name
     am = {}
     anchors = v'[]'
     pos_map = {}
     for i, anchor in enumerate(tam[name] or v'[]'):
-        val = anchor_funcs.pos_for_elem()
-        if anchor.frag:
-            elem = document.getElementById(anchor.frag)
-            if elem:
-                val = anchor_funcs.pos_for_elem(elem)
-        am[anchor.id] = val
+        am[anchor.id] = position_for_anchor(anchor.frag)
         anchors.push(anchor.id)
         pos_map[anchor.id] = i
+    anchor_funcs = get_boss().anchor_funcs
     # stable sort by position in document
     anchors.sort(def (a, b): return anchor_funcs.cmp(am[a], am[b]) or (pos_map[a] - pos_map[b]);)
 
@@ -220,20 +221,21 @@ def recalculate_toc_anchor_positions(tam, anchor_funcs):
     return current_map
 
 
-def current_toc_anchor_map(tam, anchor_funcs):
+def current_toc_anchor_map(tam):
     current_map = toc_anchor_map()
     if not (current_map and current_map.layout_mode is current_layout_mode() and current_map.width is scroll_viewport.width() and current_map.height is scroll_viewport.height()):
-        current_map = recalculate_toc_anchor_positions(tam, anchor_funcs)
+        current_map = recalculate_toc_anchor_positions(tam)
     return current_map
 
 
-def update_visible_toc_anchors(toc_anchor_map, anchor_funcs, recalculate):
+def update_visible_toc_anchors(toc_anchor_map, recalculate):
     if recalculate:
-        recalculate_toc_anchor_positions(toc_anchor_map, anchor_funcs)
-    tam = current_toc_anchor_map(toc_anchor_map, anchor_funcs)
+        recalculate_toc_anchor_positions(toc_anchor_map)
+    tam = current_toc_anchor_map(toc_anchor_map)
     before = after = None
     visible_anchors = {}
     has_visible = False
+    anchor_funcs = get_boss().anchor_funcs
 
     for anchor_id in tam.sorted_anchors:
         pos = tam.pos_map[anchor_id]
@@ -250,10 +252,10 @@ def update_visible_toc_anchors(toc_anchor_map, anchor_funcs, recalculate):
     return {'visible_anchors':visible_anchors, 'has_visible':has_visible, 'before':before, 'after':after, 'sorted_anchors':tam.sorted_anchors}
 
 
-def find_anchor_before_range(r, toc_anchor_map, anchor_funcs):
+def find_anchor_before_range(r, toc_anchor_map):
     name = current_spine_item().name
     prev_anchor = None
-    tam = current_toc_anchor_map(toc_anchor_map, anchor_funcs)
+    tam = current_toc_anchor_map(toc_anchor_map)
     anchors = toc_anchor_map[name]
     if anchors:
         amap = {x.id: x for x in anchors}