Merge branch 'bvolpato/vertical-tab-bar-side' of https://github.com/bvolpato/kitty

kitty/boss.py

@@ -2017,7 +2017,7 @@ def on_drop(self, os_window_id: int, drop: dict[str, bytes] | int, from_self: bo
                             window.on_drop(drop)
                             break
         elif tab_bar.left <= x < tab_bar.right and tab_bar.top <= y < tab_bar.bottom:
-            if (tab_id := tm.tab_bar.tab_id_at(x)) and (tab := self.tab_for_id(tab_id)) and (w := tab.active_window):
+            if (tab_id := tm.tab_bar.tab_id_at(x, y)) and (tab := self.tab_for_id(tab_id)) and (w := tab.active_window):
                 w.on_drop(drop)
 
     def on_drag_source_finished(

kitty/mouse.c

@@ -1010,6 +1010,8 @@ mouse_region(bool detect_borders, bool detect_title_bar) {
     const bool in_central = mouse_in_region(&central);
     if (!in_central) {
         if (
+                (tab_bar.left < central.left && w->mouse_x < central.left) ||
+                (tab_bar.right > central.right && w->mouse_x >= central.right) ||
                 (tab_bar.top < central.top && w->mouse_y < central.top) ||
                 (tab_bar.bottom > central.bottom && w->mouse_y >= central.bottom)
            ) ans.in_tab_bar = true;

kitty/options/definition.py

@@ -1616,18 +1616,22 @@
 
 opt('tab_bar_edge', 'bottom',
     option_type='tab_bar_edge', ctype='int',
-    long_text='The edge to show the tab bar on, :code:`top` or :code:`bottom`.'
+    long_text='The edge to show the tab bar on, :code:`top`, :code:`bottom`, :code:`left` or :code:`right`.'
     )
 
 opt('tab_bar_margin_width', '0.0',
     option_type='positive_float',
-    long_text='The margin to the left and right of the tab bar (in pts).'
+    long_text='''
+The margin perpendicular to the tab bar edge (in pts). For tab bars on the
+top or bottom this is the margin to the left and right. For tab bars on the
+left or right this is the margin above and below.
+'''
     )
 
 opt('tab_bar_margin_height', '0.0 0.0',
     option_type='tab_bar_margin_height', ctype='!tab_bar_margin_height',
     long_text='''
-The margin above and below the tab bar (in pts). The first number is the margin
+The margin along the tab bar edge (in pts). The first number is the margin
 between the edge of the OS Window and the tab bar. The second number is the
 margin between the tab bar and the contents of the current tab.
 '''
@@ -1675,11 +1679,12 @@
 are automatically restricted to work only on matching tabs.
 ''')
 
-opt('tab_bar_align', 'left',
+opt('tab_bar_align', 'start',
-    choices=('left', 'center', 'right'),
+    choices=('start', 'center', 'end', 'left', 'right'),
     long_text='''
-The horizontal alignment of the tab bar, can be one of: :code:`left`,
+The alignment of the tab bar, can be one of: :code:`start`, :code:`center`,
-:code:`center`, :code:`right`.
+:code:`end`, :code:`left`, :code:`right`. The values :code:`left` and
+:code:`right` are aliases for :code:`start` and :code:`end` respectively.
 '''
     )
 
@@ -1746,10 +1751,12 @@
     )
 
 opt('tab_title_max_length', '0',
-    option_type='positive_int',
+    option_type='positive_int', ctype='int',
     long_text='''
 The maximum number of cells that can be used to render the text in a tab.
-A value of zero means that no limit is applied.
+A value of zero means that no limit is applied. For vertical tab bars, kitty
+uses a default sidebar width sized for about twenty title cells when this is
+left unset.
 '''
     )
 

kitty/options/parse.py

@@ -1356,7 +1356,7 @@ def tab_bar_align(self, val: str, ans: dict[str, typing.Any]) -> None:
             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'))
+    choices_for_tab_bar_align = frozenset(('start', 'center', 'end', 'left', 'right'))
 
     def tab_bar_background(self, val: str, ans: dict[str, typing.Any]) -> None:
         ans['tab_bar_background'] = to_color_or_none(val)
@@ -1558,7 +1558,7 @@ def window_title_bar_align(self, val: str, ans: dict[str, typing.Any]) -> None:
             raise ValueError(f"The value {val} is not a valid choice for window_title_bar_align")
         ans["window_title_bar_align"] = val
 
-    choices_for_window_title_bar_align = choices_for_tab_bar_align
+    choices_for_window_title_bar_align = frozenset(('left', 'center', 'right'))
 
     def window_title_bar_inactive_background(self, val: str, ans: dict[str, typing.Any]) -> None:
         ans['window_title_bar_inactive_background'] = to_color_or_none(val)

kitty/options/to-c-generated.h

@@ -1110,6 +1110,19 @@ convert_from_opts_tab_bar_style(PyObject *py_opts, Options *opts) {
     Py_DECREF(ret);
 }
 
+static void
+convert_from_python_tab_title_max_length(PyObject *val, Options *opts) {
+    opts->tab_title_max_length = PyLong_AsLong(val);
+}
+
+static void
+convert_from_opts_tab_title_max_length(PyObject *py_opts, Options *opts) {
+    PyObject *ret = PyObject_GetAttrString(py_opts, "tab_title_max_length");
+    if (ret == NULL) return;
+    convert_from_python_tab_title_max_length(ret, opts);
+    Py_DECREF(ret);
+}
+
 static void
 convert_from_python_tab_bar_background(PyObject *val, Options *opts) {
     opts->tab_bar_background = color_or_none_as_int(val);
@@ -1659,6 +1672,8 @@ convert_opts_from_python_opts(PyObject *py_opts, Options *opts) {
     if (PyErr_Occurred()) return false;
     convert_from_opts_tab_bar_style(py_opts, opts);
     if (PyErr_Occurred()) return false;
+    convert_from_opts_tab_title_max_length(py_opts, opts);
+    if (PyErr_Occurred()) return false;
     convert_from_opts_tab_bar_background(py_opts, opts);
     if (PyErr_Occurred()) return false;
     convert_from_opts_tab_bar_margin_color(py_opts, opts);

kitty/options/types.py

@@ -32,7 +32,7 @@
 choices_for_progress_bar = typing.Literal['left', 'right', 'top', 'bottom', 'hidden']
 choices_for_scrollbar = typing.Literal['scrolled', 'always', 'never', 'hovered', 'scrolled-and-hovered']
 choices_for_strip_trailing_spaces = typing.Literal['always', 'never', 'smart']
-choices_for_tab_bar_align = typing.Literal['left', 'center', 'right']
+choices_for_tab_bar_align = typing.Literal['start', 'center', 'end', 'left', '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']
@@ -41,7 +41,7 @@
 choices_for_underline_hyperlinks = typing.Literal['hover', 'always', 'never']
 choices_for_window_logo_position = choices_for_placement_strategy
 choices_for_window_title_bar = typing.Literal['top', 'bottom']
-choices_for_window_title_bar_align = choices_for_tab_bar_align
+choices_for_window_title_bar_align = typing.Literal['left', 'center', 'right']
 
 option_names = (
     'action_alias',
@@ -666,7 +666,7 @@ class Options:
     strip_trailing_spaces: choices_for_strip_trailing_spaces = 'never'
     sync_to_monitor: bool = True
     tab_activity_symbol: str = ''
-    tab_bar_align: choices_for_tab_bar_align = 'left'
+    tab_bar_align: choices_for_tab_bar_align = 'start'
     tab_bar_background: kitty.fast_data_types.Color | None = None
     tab_bar_edge: int = 8
     tab_bar_filter: str = ''

kitty/options/utils.py

@@ -751,7 +751,12 @@ def tab_separator(x: str) -> str:
 
 
 def tab_bar_edge(x: str) -> int:
-    return {'top': defines.TOP_EDGE, 'bottom': defines.BOTTOM_EDGE}.get(x.lower(), defines.BOTTOM_EDGE)
+    return {
+        'left': defines.LEFT_EDGE,
+        'top': defines.TOP_EDGE,
+        'right': defines.RIGHT_EDGE,
+        'bottom': defines.BOTTOM_EDGE,
+    }.get(x.lower(), defines.BOTTOM_EDGE)
 
 
 def tab_font_style(x: str) -> tuple[bool, bool]:

kitty/state.c

@@ -691,29 +691,76 @@ pyset_borders_rects(PyObject *self UNUSED, PyObject *args) {
 }
 
 
+static unsigned
+vertical_tab_bar_cols(const OSWindow *os_window, long margin_outer, long margin_inner) {
+    unsigned cell_width = MAX(1u, os_window->fonts_data->fcm.cell_width);
+    long available_width = (long)os_window->viewport_width - margin_outer - margin_inner;
+    if (available_width <= 0) return 0;
+    unsigned available_cols = MAX(1u, (unsigned)available_width / cell_width);
+    unsigned title_cols = OPT(tab_title_max_length) > 0 ? (unsigned)OPT(tab_title_max_length) : 20u;
+    unsigned desired_cols = title_cols + 8u;
+    unsigned soft_max = available_cols / 3u;
+    if (soft_max < 6u) soft_max = available_cols;
+    return MAX(1u, MIN(available_cols, MIN(desired_cols, MAX(1u, soft_max))));
+}
+
 void
 os_window_regions(const OSWindow *os_window, Region *central, Region *tab_bar) {
     if (!OPT(tab_bar_hidden) && os_window->num_tabs && !os_window->has_too_few_tabs) {
         long margin_outer = pt_to_px_for_os_window(OPT(tab_bar_margin_height.outer), os_window);
         long margin_inner = pt_to_px_for_os_window(OPT(tab_bar_margin_height.inner), os_window);
         central->left = 0; central->right = os_window->viewport_width;
-        unsigned tab_bar_height = os_window->fonts_data->fcm.cell_height + margin_inner + margin_outer;
+        central->top = 0; central->bottom = os_window->viewport_height;
         switch(OPT(tab_bar_edge)) {
-            case TOP_EDGE:
+            case TOP_EDGE: {
+                unsigned tab_bar_height = os_window->fonts_data->fcm.cell_height + margin_inner + margin_outer;
                 central->top = tab_bar_height;
                 central->bottom = os_window->viewport_height;
                 central->top = MIN(central->top, central->bottom);
                 tab_bar->top = margin_outer;
+                tab_bar->left = central->left; tab_bar->right = central->right;
+                tab_bar->bottom = tab_bar->top + os_window->fonts_data->fcm.cell_height;
                 break;
-            default:
+            }
+            case LEFT_EDGE: {
+                unsigned left_cols = vertical_tab_bar_cols(os_window, margin_outer, margin_inner);
+                if (!left_cols) {
+                    zero_at_ptr(tab_bar);
+                    return;
+                }
+                unsigned left_width = left_cols * os_window->fonts_data->fcm.cell_width;
+                central->left = MIN((long)(left_width + margin_inner + margin_outer), (long)central->right);
+                tab_bar->left = margin_outer;
+                tab_bar->right = tab_bar->left + left_width;
+                tab_bar->top = central->top;
+                tab_bar->bottom = central->bottom;
+                break;
+            }
+            case RIGHT_EDGE: {
+                unsigned right_cols = vertical_tab_bar_cols(os_window, margin_outer, margin_inner);
+                if (!right_cols) {
+                    zero_at_ptr(tab_bar);
+                    return;
+                }
+                unsigned right_width = right_cols * os_window->fonts_data->fcm.cell_width;
+                central->right = MAX(0, (long)os_window->viewport_width - (long)(right_width + margin_inner + margin_outer));
+                tab_bar->left = central->right + margin_inner;
+                tab_bar->right = tab_bar->left + right_width;
+                tab_bar->top = central->top;
+                tab_bar->bottom = central->bottom;
+                break;
+            }
+            default: {
+                unsigned tab_bar_height = os_window->fonts_data->fcm.cell_height + margin_inner + margin_outer;
                 central->top = 0;
                 long bottom = os_window->viewport_height - tab_bar_height;
                 central->bottom = MAX(0, bottom);
                 tab_bar->top = central->bottom + margin_inner;
-                break;
-        }
                 tab_bar->left = central->left; tab_bar->right = central->right;
                 tab_bar->bottom = tab_bar->top + os_window->fonts_data->fcm.cell_height;
+                break;
+            }
+        }
     } else {
         zero_at_ptr(tab_bar);
         central->left = 0; central->top = 0; central->right = os_window->viewport_width;

kitty/state.h

@@ -110,6 +110,7 @@ typedef struct Options {
     bool dynamic_background_opacity;
     float inactive_text_alpha;
     Edge tab_bar_edge;
+    int tab_title_max_length;
     DisableLigature disable_ligatures;
     bool force_ltr;
     bool resize_in_steps;

kitty/tab_bar.py

@@ -17,8 +17,11 @@
     BOTTOM_EDGE,
     DECAWM,
     Color,
+    LEFT_EDGE,
     Region,
+    RIGHT_EDGE,
     Screen,
+    TOP_EDGE,
     background_opacity_of,
     cell_size_for_window,
     get_boss,
@@ -101,6 +104,31 @@ def as_rgb(x: int) -> int:
     return (x << 8) | 2
 
 
+VERTICAL_EDGES = frozenset({LEFT_EDGE, RIGHT_EDGE})
+MAX_VERTICAL_TAB_LINES = 2
+
+
+def is_vertical_edge(edge: int) -> bool:
+    return edge in VERTICAL_EDGES
+
+
+def edge_name(edge: int) -> EdgeLiteral:
+    return {
+        LEFT_EDGE: 'left',
+        TOP_EDGE: 'top',
+        RIGHT_EDGE: 'right',
+        BOTTOM_EDGE: 'bottom',
+    }.get(edge, 'bottom')
+
+
+def normalized_tab_bar_align(align: str) -> str:
+    if align == 'left':
+        return 'start'
+    if align == 'right':
+        return 'end'
+    return align
+
+
 @lru_cache
 def report_template_failure(template: str, e: str) -> None:
     log_error(f'Invalid tab title template: "{template}" with error: {e}')
@@ -342,7 +370,7 @@ def draw_tab_with_slant(
     extra_data: ExtraData
 ) -> int:
     orig_fg = screen.cursor.fg
-    left_sep, right_sep = ('', '') if draw_data.tab_bar_edge == 'top' else ('', '')
+    left_sep, right_sep = ('', '') if draw_data.tab_bar_edge in ('top', 'left') else ('', '')
     tab_bg = screen.cursor.bg
     slant_fg = as_rgb(color_as_int(draw_data.default_bg))
 
@@ -567,10 +595,18 @@ class CellRange(NamedTuple):
 
 class TabExtent(NamedTuple):
     tab_id: int
-    cell_range: CellRange
+    x: CellRange
+    y: CellRange = CellRange(0, 0)
 
-    def shifted(self, shift: int) -> 'TabExtent':
+    def shifted(self, x: int = 0, y: int = 0) -> 'TabExtent':
-        return TabExtent(self.tab_id, CellRange(self.cell_range.start + shift, self.cell_range.end + shift))
+        return TabExtent(
+            self.tab_id,
+            CellRange(self.x.start + x, self.x.end + x),
+            CellRange(self.y.start + y, self.y.end + y),
+        )
+
+    def contains(self, x: int, y: int) -> bool:
+        return self.x.start <= x <= self.x.end and self.y.start <= y <= self.y.end
 
 
 class TabBar:
@@ -588,6 +624,8 @@ def __init__(self, os_window_id: int):
     def apply_options(self) -> None:
         opts = get_options()
         self.dirty = True
+        self.tab_bar_edge = opts.tab_bar_edge
+        self.is_vertical = is_vertical_edge(opts.tab_bar_edge)
         self.margin_width = pt_to_px(opts.tab_bar_margin_width, self.os_window_id)
         self.cell_width, cell_height = cell_size_for_window(self.os_window_id)
         if not hasattr(self, 'screen'):
@@ -618,7 +656,7 @@ def apply_options(self) -> None:
             opts.active_tab_title_template,
             opts.tab_activity_symbol,
             opts.tab_powerline_style,
-            'bottom' if opts.tab_bar_edge == BOTTOM_EDGE else 'top',
+            edge_name(opts.tab_bar_edge),
             opts.tab_title_max_length, self.os_window_id,
         )
         ts = opts.tab_bar_style
@@ -632,9 +670,16 @@ def apply_options(self) -> None:
             self.draw_func = load_custom_draw_tab()
         else:
             self.draw_func = draw_tab_with_fade
-        if opts.tab_bar_align == 'center':
+        self.tab_bar_align = normalized_tab_bar_align(opts.tab_bar_align)
+        if self.tab_bar_align == 'center':
+            self.align_factor = 2
+        elif self.tab_bar_align == 'end':
+            self.align_factor = 1
+        else:
+            self.align_factor = 0
+        if self.tab_bar_align == 'center':
             self.align: Callable[[], None] = partial(self.align_with_factor, 2)
-        elif opts.tab_bar_align == 'right':
+        elif self.tab_bar_align == 'end':
             self.align = self.align_with_factor
         else:
             self.align = lambda: None
@@ -690,7 +735,18 @@ def update_blank_rects(self, central: Region, tab_bar: Region, vw: int, vh: int)
         blank_rects: list[Border] = []
         bg = BorderColor.tab_bar_margin_color if opts.tab_bar_margin_color is not None else BorderColor.default_bg
         if opts.tab_bar_margin_height:
-            if opts.tab_bar_edge == BOTTOM_EDGE:
+            if self.is_vertical:
+                if opts.tab_bar_edge == LEFT_EDGE:
+                    if opts.tab_bar_margin_height.outer:
+                        blank_rects.append(Border(0, 0, tab_bar.left, vh, bg))
+                    if opts.tab_bar_margin_height.inner:
+                        blank_rects.append(Border(tab_bar.right, 0, central.left, vh, bg))
+                else:
+                    if opts.tab_bar_margin_height.outer:
+                        blank_rects.append(Border(tab_bar.right, 0, vw, vh, bg))
+                    if opts.tab_bar_margin_height.inner:
+                        blank_rects.append(Border(central.right, 0, tab_bar.left, vh, bg))
+            elif opts.tab_bar_edge == BOTTOM_EDGE:
                 if opts.tab_bar_margin_height.outer:
                     blank_rects.append(Border(0, tab_bar.bottom, vw, vh, bg))
                 if opts.tab_bar_margin_height.inner:
@@ -701,23 +757,54 @@ def update_blank_rects(self, central: Region, tab_bar: Region, vw: int, vh: int)
                 if opts.tab_bar_margin_height.inner:
                     blank_rects.append(Border(0, tab_bar.bottom, vw, central.top, bg))
         g = self.window_geometry
+        if self.is_vertical:
+            if g.left > tab_bar.left:
+                blank_rects.append(Border(tab_bar.left, g.top, g.left, g.bottom, bg))
+            if g.right < tab_bar.right:
+                blank_rects.append(Border(g.right, g.top, tab_bar.right, g.bottom, bg))
+            if g.top > tab_bar.top:
+                blank_rects.append(Border(g.left, tab_bar.top, g.right, g.top, bg))
+            if g.bottom < tab_bar.bottom:
+                blank_rects.append(Border(g.left, g.bottom, g.right, tab_bar.bottom, bg))
+        else:
             left_bg = right_bg = bg
             if opts.tab_bar_margin_color is None and (
                     opacity := background_opacity_of(self.os_window_id)) is not None and opacity >= 1:
                 left_bg = BorderColor.tab_bar_left_edge_color
                 right_bg = BorderColor.tab_bar_right_edge_color
-        if g.left > 0:
+            if g.left > tab_bar.left:
-            blank_rects.append(Border(0, g.top, g.left, g.bottom, left_bg))
+                blank_rects.append(Border(tab_bar.left, g.top, g.left, g.bottom, left_bg))
-        if g.right < vw:
+            if g.right < tab_bar.right:
-            blank_rects.append(Border(g.right, g.top, vw, g.bottom, right_bg))
+                blank_rects.append(Border(g.right, g.top, tab_bar.right, g.bottom, right_bg))
+            if g.top > tab_bar.top:
+                blank_rects.append(Border(g.left, tab_bar.top, g.right, g.top, bg))
+            if g.bottom < tab_bar.bottom:
+                blank_rects.append(Border(g.left, g.bottom, g.right, tab_bar.bottom, bg))
         self.blank_rects = tuple(blank_rects)
 
     def layout(self) -> None:
         central, tab_bar, vw, vh, cell_width, cell_height = viewport_for_window(self.os_window_id)
-        if tab_bar.width < 2:
+        if self.is_vertical:
+            if tab_bar.width < cell_width or tab_bar.height < cell_height:
+                return
+        elif tab_bar.width < 2:
             return
         self.cell_width = cell_width
+        self.cell_height = cell_height
         s = self.screen
+        if self.is_vertical:
+            available_height = tab_bar.height - 2 * self.margin_width
+            nlines = max(1, available_height // cell_height)
+            ncols = max(1, tab_bar.width // cell_width)
+            s.resize(nlines, ncols)
+            s.reset_mode(DECAWM)
+            cell_area_height = nlines * cell_height
+            available_height_for_top_margin = max(0, tab_bar.height - self.margin_width - cell_area_height)
+            extra_height = max(0, tab_bar.height - 2 * self.margin_width - cell_area_height)
+            top_margin = min(self.margin_width + extra_height // 2, available_height_for_top_margin)
+            self.window_geometry = g = WindowGeometry(
+                tab_bar.left, tab_bar.top + top_margin, tab_bar.right, tab_bar.top + top_margin + cell_area_height, s.columns, s.lines)
+        else:
             available_width = tab_bar.width - 2 * self.margin_width
             ncells = max(4, available_width // cell_width)
             s.resize(1, ncells)
@@ -726,15 +813,18 @@ def layout(self) -> None:
             available_width_for_left_margin = max(0, tab_bar.width - self.margin_width - cell_area_width)
             extra_width = max(0, tab_bar.width - 2 * self.margin_width - cell_area_width)
             left_margin = min(self.margin_width + extra_width // 2, available_width_for_left_margin)
-        self.laid_out_once = True
             self.window_geometry = g = WindowGeometry(
                 left_margin, tab_bar.top, left_margin + cell_area_width, tab_bar.bottom, s.columns, s.lines)
+        self.laid_out_once = True
         self.update_blank_rects(central, tab_bar, vw, vh)
         set_tab_bar_render_data(self.os_window_id, self.screen, *g[:4])
 
     def update(self, data: Sequence[TabBarData]) -> None:
         if not self.laid_out_once:
             return
+        if self.is_vertical:
+            self.update_vertical(data)
+            return
         s = self.screen
         last_tab = data[-1] if data else None
         ed = ExtraData()
@@ -743,14 +833,14 @@ def update(self, data: Sequence[TabBarData]) -> None:
         def draw_tab(i: int, tab: TabBarData, cell_ranges: list[TabExtent], max_tab_length: int) -> None:
             ed.prev_tab = data[i - 1] if i > 0 else None
             ed.next_tab = data[i + 1] if i + 1 < len(data) else None
-            s.cursor.bg = as_rgb(self.draw_data.tab_bg(t))
+            s.cursor.bg = as_rgb(self.draw_data.tab_bg(tab))
-            s.cursor.fg = as_rgb(self.draw_data.tab_fg(t))
+            s.cursor.fg = as_rgb(self.draw_data.tab_fg(tab))
-            s.cursor.bold, s.cursor.italic = self.active_font_style if t.is_active else self.inactive_font_style
+            s.cursor.bold, s.cursor.italic = self.active_font_style if tab.is_active else self.inactive_font_style
             before = s.cursor.x
-            end = self.draw_func(self.draw_data, s, t, before, max_tab_length, i + 1, t is last_tab, ed)
+            end = self.draw_func(self.draw_data, s, tab, before, max_tab_length, i + 1, tab is last_tab, ed)
             s.cursor.bg = s.cursor.fg = 0
-            cell_ranges.append(TabExtent(tab_id=tab.tab_id, cell_range=CellRange(before, end)))
+            cell_ranges.append(TabExtent(tab_id=tab.tab_id, x=CellRange(before, end)))
-            if not ed.for_layout and t is not last_tab and s.cursor.x > s.columns - max_tab_lengths[i+1]:
+            if not ed.for_layout and tab is not last_tab and s.cursor.x > s.columns - max_tab_lengths[i+1]:
                 # Stop if there is no space for next tab
                 s.cursor.x = s.columns - 2
                 s.cursor.bg = as_rgb(color_as_int(self.draw_data.default_bg))
@@ -801,24 +891,72 @@ def draw_tab(i: int, tab: TabBarData, cell_ranges: list[TabExtent], max_tab_leng
         self.align()
         update_tab_bar_edge_colors(self.os_window_id)
 
+    def update_vertical(self, data: Sequence[TabBarData]) -> None:
+        s = self.screen
+        self.last_laid_out_tabs = data
+        self.tab_extents = ()
+        s.cursor.x = s.cursor.y = 0
+        s.erase_in_display(2, False)
+        if not data:
+            return
+        max_tab_length = max(1, s.columns - 1)
+        tab_line_height = max(1, min(MAX_VERTICAL_TAB_LINES, s.lines // max(1, len(data))))
+        rows_to_draw = min(len(data), max(1, s.lines // tab_line_height))
+        draw_ellipsis = len(data) > rows_to_draw and s.lines > 1
+        if draw_ellipsis:
+            tab_line_height = 1
+            rows_to_draw = min(len(data), s.lines)
+            rows_to_draw -= 1
+        total_lines = rows_to_draw * tab_line_height + int(draw_ellipsis)
+        if self.tab_bar_align == 'center':
+            start_row = max(0, (s.lines - total_lines) // 2)
+        elif self.tab_bar_align == 'end':
+            start_row = max(0, s.lines - total_lines)
+        else:
+            start_row = 0
+        cr: list[TabExtent] = []
+        for i, t in enumerate(data[:rows_to_draw]):
+            s.cursor.x = 0
+            row = start_row + i * tab_line_height
+            s.cursor.y = row
+            s.cursor.bg = as_rgb(self.draw_data.tab_bg(t))
+            s.cursor.fg = as_rgb(self.draw_data.tab_fg(t))
+            s.cursor.bold, s.cursor.italic = self.active_font_style if t.is_active else self.inactive_font_style
+            self.draw_func(self.draw_data, s, t, 0, max_tab_length, i + 1, True, ExtraData())
+            cr.append(TabExtent(tab_id=t.tab_id, x=CellRange(0, s.columns - 1), y=CellRange(row, min(s.lines - 1, row + tab_line_height - 1))))
+        if draw_ellipsis:
+            s.cursor.x = 0
+            s.cursor.y = start_row + rows_to_draw * tab_line_height
+            s.cursor.bg = as_rgb(color_as_int(self.draw_data.default_bg))
+            s.cursor.fg = as_rgb(0xff0000)
+            s.draw('…')
+        self.tab_extents = tuple(cr)
+
     def align_with_factor(self, factor: int = 1) -> None:
         if not self.tab_extents:
             return
-        end = self.tab_extents[-1].cell_range[1]
+        end = self.tab_extents[-1].x.end
         if end < self.screen.columns - 1:
             shift = (self.screen.columns - end) // factor
             self.screen.cursor.x = 0
             self.screen.insert_characters(shift)
-            self.tab_extents = tuple(te.shifted(shift) for te in self.tab_extents)
+            self.tab_extents = tuple(te.shifted(x=shift) for te in self.tab_extents)
 
     def destroy(self) -> None:
         self.screen.reset_callbacks()
         del self.screen
 
-    def tab_id_at(self, x: int) -> int:
+    def tab_id_at(self, x: int, y: int = 0) -> int:
         if self.laid_out_once:
-            x = (x - self.window_geometry.left) // self.cell_width
+            g = self.window_geometry
+            if not (g.left <= x < g.right and g.top <= y < g.bottom):
+                return 0
+            x = (x - g.left) // self.cell_width
+            y = (y - g.top) // self.cell_height
             for te in self.tab_extents:
-                if te.cell_range.start <= x <= te.cell_range.end:
+                if te.contains(x, y):
                     return te.tab_id
         return 0
+
+    def drag_axis_coordinate(self, x: int, y: int) -> int:
+        return y if self.is_vertical else x

kitty/tabs.py

@@ -1171,7 +1171,7 @@ def swap_windows(self, window_a: Window, window_b: Window) -> None:
 class TabBeingDropped(NamedTuple):
     data: TabBarData
     tab_ids: Sequence[int] = ()
-    last_drop_move_x: int = -1
+    last_drop_move_coordinate: int = -1
 
 
 class WindowBeingDropped(NamedTuple):
@@ -1703,27 +1703,29 @@ def on_tab_drop_move(self, tab_id: int = 0, is_dest: bool = False, x: int = 0, y
             tab_data = tab.data_for_tab_bar(tab is get_boss().active_tab)
             if tab_id not in all_tabs:
                 all_tabs.append(tab_id)
-            _, _, start_x, _ = get_tab_being_dragged()
+            _, _, start_x, start_y = get_tab_being_dragged()
-            self.tab_being_dropped = TabBeingDropped(data=tab_data, tab_ids=all_tabs, last_drop_move_x=int(start_x))
+            start_coordinate = self.tab_bar.drag_axis_coordinate(int(start_x), int(start_y))
-            mouse_moved_left = False
+            self.tab_being_dropped = TabBeingDropped(data=tab_data, tab_ids=all_tabs, last_drop_move_coordinate=start_coordinate)
             force_update = True
-        if x == self.tab_being_dropped.last_drop_move_x and not force_update:
+        coordinate = self.tab_bar.drag_axis_coordinate(x, y)
+        if coordinate == self.tab_being_dropped.last_drop_move_coordinate and not force_update:
             return
-        mouse_moved_left = x < self.tab_being_dropped.last_drop_move_x
+        mouse_moved_towards_start = coordinate < self.tab_being_dropped.last_drop_move_coordinate
         old_tab_ids = self.tab_being_dropped.tab_ids
         idx_under_mouse = -1
-        if (tab_id_under_mouse := self.tab_bar.tab_id_at(x)):
+        if (tab_id_under_mouse := self.tab_bar.tab_id_at(x, y)):
             with suppress(Exception):
                 idx_under_mouse = old_tab_ids.index(tab_id_under_mouse)
         if idx_under_mouse < 0:
-            idx_under_mouse = 0 if x < 20 else len(old_tab_ids) - 1
+            start = self.tab_bar.window_geometry.top if self.tab_bar.is_vertical else self.tab_bar.window_geometry.left
+            idx_under_mouse = 0 if coordinate < start else len(old_tab_ids) - 1
         old_idx_under_mouse = old_tab_ids.index(tab_id)
-        idx_moved_left = old_idx_under_mouse > idx_under_mouse
+        idx_moved_towards_start = old_idx_under_mouse > idx_under_mouse
         new_tab_ids = old_tab_ids
-        if mouse_moved_left == idx_moved_left:
+        if mouse_moved_towards_start == idx_moved_towards_start:
             new_tab_ids = list(old_tab_ids)
             new_tab_ids[idx_under_mouse], new_tab_ids[old_idx_under_mouse] = new_tab_ids[old_idx_under_mouse], new_tab_ids[idx_under_mouse]
-        self.tab_being_dropped = self.tab_being_dropped._replace(last_drop_move_x=x, tab_ids=new_tab_ids)
+        self.tab_being_dropped = self.tab_being_dropped._replace(last_drop_move_coordinate=coordinate, tab_ids=new_tab_ids)
         if force_update or self.tab_being_dropped.tab_ids != old_tab_ids:
             self.layout_tab_bar()
 
@@ -1803,11 +1805,11 @@ def handle_tab_bar_mouse(self, x: float, y: float, button: int, modifiers: int,
                     self.recent_tab_bar_mouse_events.clear()
             return
 
-        tab_id_at_x = self.tab_bar.tab_id_at(int(x))
+        tab_id_at_pointer = self.tab_bar.tab_id_at(int(x), int(y))
-        self.recent_tab_bar_mouse_events.add(button, modifiers, action, x, y, tab_id_at_x)
+        self.recent_tab_bar_mouse_events.add(button, modifiers, action, x, y, tab_id_at_pointer)
         drag_started = get_tab_being_dragged()[1]
         is_left_release = button == GLFW_MOUSE_BUTTON_LEFT and action == GLFW_RELEASE
-        if tab_id_at_x < 0:  # synthetic tab (e.g. "+" new-tab button)
+        if tab_id_at_pointer < 0:  # synthetic tab (e.g. "+" new-tab button)
             if is_left_release and not drag_started:
                 set_tab_being_dragged()  # clear potential drag from a press on a tab
             if self.recent_tab_bar_mouse_events.click_count(GLFW_MOUSE_BUTTON_LEFT) == 1:
@@ -1816,7 +1818,7 @@ def handle_tab_bar_mouse(self, x: float, y: float, button: int, modifiers: int,
             return
         if drag_started:
             return
-        tab = self.tab_for_id(tab_id_at_x)
+        tab = self.tab_for_id(tab_id_at_pointer)
         if tab is None:
             if is_left_release:
                 set_tab_being_dragged()  # clear potential drag from a press on a tab
@@ -1978,7 +1980,7 @@ def on_window_drop_move(self, window_id: int = 0, is_dest: bool = False, x: int
         tab_bar = viewport_for_window(self.os_window_id)[1]
         if tab_bar.left <= x < tab_bar.right and tab_bar.top <= y < tab_bar.bottom:
             self._set_drag_target_window(0)
-            self._set_drag_target_tab(self.tab_bar.tab_id_at(x))
+            self._set_drag_target_tab(self.tab_bar.tab_id_at(x, y))
             return
         self._set_drag_target_tab(0)
         dest_window = self._find_window_at(x, y)
@@ -2033,7 +2035,7 @@ def on_window_drop(self, x: int, y: int, window_id: int) -> None:
         # Case 1: Drop on tab bar → move to that tab
         in_tab_bar = tab_bar.left <= x < tab_bar.right and tab_bar.top <= y < tab_bar.bottom
         if in_tab_bar:
-            if (tab_id := self.tab_bar.tab_id_at(x)) and (dest_tab := self.tab_for_id(tab_id)):
+            if (tab_id := self.tab_bar.tab_id_at(x, y)) and (dest_tab := self.tab_for_id(tab_id)):
                 boss._move_window_to(w, target_tab_id=dest_tab.id)
             else:
                 boss._move_window_to(w, target_tab_id='new')

kitty_tests/options.py

@@ -220,6 +220,7 @@ def pn(cmdline, **assertions):
 def conf_parsing(self):
     from kitty.config import defaults, load_config
     from kitty.constants import is_macos
+    from kitty.fast_data_types import LEFT_EDGE, RIGHT_EDGE
     from kitty.fonts import FontModification, ModificationType, ModificationUnit, ModificationValue
     from kitty.options.utils import to_modifiers
     bad_lines = []
@@ -254,6 +255,18 @@ def keys_for_func(opts, name):
     self.ae(opts.url_excluded_characters, "'''")
     opts = p("url_excluded_characters abc'")
     self.ae(opts.url_excluded_characters, "abc'")
+    opts = p('tab_bar_edge left')
+    self.ae(opts.tab_bar_edge, LEFT_EDGE)
+    opts = p('tab_bar_edge right')
+    self.ae(opts.tab_bar_edge, RIGHT_EDGE)
+    opts = p('tab_bar_align start')
+    self.ae(opts.tab_bar_align, 'start')
+    opts = p('tab_bar_align end')
+    self.ae(opts.tab_bar_align, 'end')
+    opts = p('tab_bar_align left')
+    self.ae(opts.tab_bar_align, 'left')
+    opts = p('tab_bar_align right')
+    self.ae(opts.tab_bar_align, 'right')
     opts = p('clear_all_shortcuts y', 'map f1 next_window')
     self.ae(len(opts.keyboard_modes[''].keymap), 1)
     opts = p('clear_all_mouse_actions y', 'mouse_map left click ungrabbed mouse_click_url_or_select')

kitty_tests/tab_bar.py

@@ -0,0 +1,89 @@
+#!/usr/bin/env python
+# License: GPL v3 Copyright: 2026, Kovid Goyal <kovid at kovidgoyal.net>
+
+from unittest.mock import patch
+
+from kitty.fast_data_types import LEFT_EDGE, Region
+from kitty.tab_bar import TabBar, TabBarData
+
+from . import BaseTest
+
+
+def region(left: int, top: int, right: int, bottom: int) -> Region:
+    return Region((left, top, right, bottom, right - left, bottom - top))
+
+
+class DummyBoss:
+    class mappings:
+        current_keyboard_mode_name = ''
+
+    def tab_for_id(self, tab_id: int) -> None:
+        return None
+
+
+class TestTabBar(BaseTest):
+
+    def test_vertical_tab_bar_hit_testing(self) -> None:
+        self.set_options({
+            'tab_bar_edge': LEFT_EDGE,
+            'tab_bar_style': 'separator',
+            'tab_title_template': '{title}',
+        })
+        central = region(120, 0, 400, 160)
+        tab_bar = region(0, 0, 120, 160)
+        geometries: list[tuple[int, int, int, int]] = []
+        boss = DummyBoss()
+
+        with (
+            patch('kitty.tab_bar.cell_size_for_window', return_value=(10, 20)),
+            patch('kitty.tab_bar.viewport_for_window', return_value=(central, tab_bar, 400, 160, 10, 20)),
+            patch('kitty.tab_bar.set_tab_bar_render_data', side_effect=lambda *args: geometries.append(args[2:6])),
+            patch('kitty.tab_bar.get_boss', return_value=boss),
+        ):
+            tb = TabBar(1)
+            tb.layout()
+            tb.update((
+                TabBarData(title='one', tab_id=1, is_active=True),
+                TabBarData(title='two', tab_id=2),
+                TabBarData(title='three', tab_id=3),
+            ))
+
+        self.assertTrue(tb.is_vertical)
+        self.ae(geometries[-1], (0, 0, 120, 160))
+        self.ae(tb.drag_axis_coordinate(5, 35), 35)
+        self.ae(tb.tab_id_at(5, 10), 1)
+        self.ae(tb.tab_id_at(110, 35), 1)
+        self.ae(tb.tab_id_at(60, 55), 2)
+        self.ae(tb.tab_id_at(60, 95), 3)
+        self.ae(tb.tab_id_at(60, 135), 0)
+        self.ae(tb.tab_id_at(180, 10), 0)
+
+    def test_vertical_tab_bar_alignment(self) -> None:
+        self.set_options({
+            'tab_bar_align': 'end',
+            'tab_bar_edge': LEFT_EDGE,
+            'tab_bar_style': 'separator',
+            'tab_title_template': '{title}',
+        })
+        central = region(120, 0, 400, 160)
+        tab_bar = region(0, 0, 120, 160)
+        boss = DummyBoss()
+
+        with (
+            patch('kitty.tab_bar.cell_size_for_window', return_value=(10, 20)),
+            patch('kitty.tab_bar.viewport_for_window', return_value=(central, tab_bar, 400, 160, 10, 20)),
+            patch('kitty.tab_bar.set_tab_bar_render_data'),
+            patch('kitty.tab_bar.get_boss', return_value=boss),
+        ):
+            tb = TabBar(1)
+            tb.layout()
+            tb.update((
+                TabBarData(title='one', tab_id=1, is_active=True),
+                TabBarData(title='two', tab_id=2),
+            ))
+
+        self.ae(tb.tab_extents[0].y, (4, 5))
+        self.ae(tb.tab_extents[1].y, (6, 7))
+        self.ae(tb.tab_id_at(5, 10), 0)
+        self.ae(tb.tab_id_at(5, 110), 1)
+        self.ae(tb.tab_id_at(5, 150), 2)