A new option to draw the tab bar centered or right

Fixes #3946

docs/changelog.rst

@@ -7,6 +7,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 0.23.2 [future]
 ----------------------
 
+- A new option :option:`tab_bar_align` to draw the tab bar centered or right
+  aligned (:iss:`3946`)
+
 - Allow the user to supply a custom Python function to draw tab bar. See
   :option:`tab_bar_style`
 

kitty/fast_data_types.pyi

@@ -1058,6 +1058,9 @@ class Screen:
     def has_activity_since_last_focus(self) -> bool:
         pass
 
+    def insert_characters(self, num: int) -> None:
+        pass
+
 
 def set_tab_bar_render_data(
     os_window_id: int, xstart: float, ystart: float, dx: float, dy: float,

kitty/options/definition.py

@@ -907,6 +907,8 @@ The tab bar style, can be one of:
 '''
     )
 
+opt('tab_bar_align', 'left', choices=('left', 'center', 'right'), long_text='The horizontal alignment of the tab bar')
+
 opt('tab_bar_min_tabs', '2',
     option_type='tab_bar_min_tabs', ctype='uint',
     long_text='The minimum number of tabs that must exist before the tab bar is shown'

kitty/options/parse.py

@@ -1152,6 +1152,14 @@ class Parser:
     def tab_activity_symbol(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
         ans['tab_activity_symbol'] = tab_activity_symbol(val)
 
+    def tab_bar_align(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
+        val = val.lower()
+        if val not in self.choices_for_tab_bar_align:
+            raise ValueError(f"The value {val} is not a valid choice for tab_bar_align")
+        ans["tab_bar_align"] = val
+
+    choices_for_tab_bar_align = frozenset(('left', 'center', 'right'))
+
     def tab_bar_background(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
         ans['tab_bar_background'] = to_color_or_none(val)
 

kitty/options/types.py

@@ -23,6 +23,7 @@ if typing.TYPE_CHECKING:
     choices_for_pointer_shape_when_dragging = typing.Literal['arrow', 'beam', 'hand']
     choices_for_pointer_shape_when_grabbed = typing.Literal['arrow', 'beam', 'hand']
     choices_for_strip_trailing_spaces = typing.Literal['always', 'never', 'smart']
+    choices_for_tab_bar_align = typing.Literal['left', 'center', 'right']
     choices_for_tab_bar_style = typing.Literal['fade', 'hidden', 'powerline', 'separator', 'slant', 'custom']
     choices_for_tab_powerline_style = typing.Literal['angled', 'round', 'slanted']
     choices_for_tab_switch_strategy = typing.Literal['last', 'left', 'previous', 'right']
@@ -35,6 +36,7 @@ else:
     choices_for_pointer_shape_when_dragging = str
     choices_for_pointer_shape_when_grabbed = str
     choices_for_strip_trailing_spaces = str
+    choices_for_tab_bar_align = str
     choices_for_tab_bar_style = str
     choices_for_tab_powerline_style = str
     choices_for_tab_switch_strategy = str
@@ -404,6 +406,7 @@ option_names = (  # {{{
  'symbol_map',
  'sync_to_monitor',
  'tab_activity_symbol',
+ 'tab_bar_align',
  'tab_bar_background',
  'tab_bar_edge',
  'tab_bar_margin_height',
@@ -536,6 +539,7 @@ class Options:
     strip_trailing_spaces: choices_for_strip_trailing_spaces = 'never'
     sync_to_monitor: bool = True
     tab_activity_symbol: typing.Optional[str] = None
+    tab_bar_align: choices_for_tab_bar_align = 'left'
     tab_bar_background: typing.Optional[kitty.rgb.Color] = None
     tab_bar_edge: int = 3
     tab_bar_margin_height: TabBarMarginHeight = TabBarMarginHeight(outer=0, inner=0)

kitty/tab_bar.py

@@ -3,7 +3,7 @@
 # License: GPL v3 Copyright: 2018, Kovid Goyal <kovid at kovidgoyal.net>
 
 import os
-from functools import lru_cache, wraps
+from functools import lru_cache, partial, wraps
 from typing import (
     Any, Callable, Dict, List, NamedTuple, Optional, Sequence, Tuple
 )
@@ -415,6 +415,12 @@ class TabBar:
             self.draw_func = load_custom_draw_tab()
         else:
             self.draw_func = draw_tab_with_fade
+        if opts.tab_bar_align == 'center':
+            self.align: Callable[[], None] = partial(self.align_with_factor, 2)
+        elif opts.tab_bar_align == 'right':
+            self.align = self.align_with_factor
+        else:
+            self.align = lambda: None
 
     def patch_colors(self, spec: Dict[str, Any]) -> None:
         if 'active_tab_foreground' in spec:
@@ -497,6 +503,17 @@ class TabBar:
                 break
         s.erase_in_line(0, False)  # Ensure no long titles bleed after the last tab
         self.cell_ranges = cr
+        self.align()
+
+    def align_with_factor(self, factor: int = 1) -> None:
+        if not self.cell_ranges:
+            return
+        end = self.cell_ranges[-1][1]
+        if end < self.screen.columns - 1:
+            shift = (self.screen.columns - end) // factor
+            self.screen.cursor.x = 0
+            self.screen.insert_characters(shift)
+            self.cell_ranges = [(s + shift, e + shift) for (s, e) in self.cell_ranges]
 
     def destroy(self) -> None:
         self.screen.reset_callbacks()