When viewing the scrollback in less and kitty is currently scrolled, position the scrollback in less to match kitty's scroll position.

Fixes #148

docs/changelog.rst

@@ -21,6 +21,10 @@ Changelog
 - Implement changing the font size for individual top level (OS) windows
   (:iss:`408`)
 
+- When viewing the scrollback in less using :sc:`show_scrollback` and kitty
+  is currently scrolled, position the scrollback in less to match kitty's
+  scroll position. (:iss:`148`)
+
 - ssh kitten: Support all SSH options. It can now be aliased directly to ssh
   for convenience. (:pull:`591`)
 

kitty/boss.py

@@ -528,12 +528,12 @@ class Boss:
         for window_id in tuple(w.id for w in self.window_id_map.values() if getattr(w, 'os_window_id', None) == os_window_id):
             self.window_id_map.pop(window_id, None)
 
-    def display_scrollback(self, window, data):
+    def display_scrollback(self, window, data, cmd):
         tab = self.active_tab
         if tab is not None and window.overlay_for is None:
             tab.new_special_window(
                 SpecialWindow(
-                    self.opts.scrollback_pager, data, _('History'), overlay_for=window.id))
+                    cmd, data, _('History'), overlay_for=window.id))
 
     def edit_config_file(self, *a):
         confpath = prepare_config_file_for_editing()

kitty/config_data.py

@@ -275,10 +275,12 @@ o('scrollback_lines', 2000, option_type=positive_int, long_text=_('''
 Number of lines of history to keep in memory for scrolling back. Memory is allocated
 on demand.'''))
 
-o('scrollback_pager', 'less +G -R', option_type=to_cmdline, long_text=_('''
+o('scrollback_pager', 'less --RAW-CONTROL-CHARS +INPUT_LINE_NUMBER', option_type=to_cmdline, long_text=_('''
 Program with which to view scrollback in a new window. The scrollback buffer is
 passed as STDIN to this program. If you change it, make sure the program you
-use can handle ANSI escape sequences for colors and text formatting.'''))
+use can handle ANSI escape sequences for colors and text formatting.
+INPUT_LINE_NUMBER in the command line above will be replaced by an integer
+representing which line should be at the top of the screen.'''))
 
 o('wheel_scroll_multiplier', 5.0, long_text=_('''
 Modify the amount scrolled by the mouse wheel or touchpad. Use

kitty/window.py

@@ -418,7 +418,12 @@ class Window:
     # actions {{{
 
     def show_scrollback(self):
-        get_boss().display_scrollback(self, self.as_text(as_ansi=True, add_history=True).encode('utf-8'))
+        data = self.as_text(as_ansi=True, add_history=True, add_wrap_markers=True)
+        data = data.replace('\r\n', '\n').replace('\r', '\n')
+        lines = data.count('\n')
+        input_line_number = (lines - (self.screen.lines - 1) - self.screen.scrolled_by)
+        cmd = [x.replace('INPUT_LINE_NUMBER', str(input_line_number)) for x in self.opts.scrollback_pager]
+        get_boss().display_scrollback(self, data, cmd)
 
     def paste(self, text):
         if text and not self.destroyed: