A new tab bar style

docs/changelog.rst

@@ -6,18 +6,23 @@ Changelog
 0.11.0 [future]
 ------------------------------
 
+- A new tab bar style "fade" in which each tabs edges fade into the background.
+  See :opt:`tab_bar_style` and :opt:`tab_fade` for details. The old look can be
+  restored by setting tab_bar_style to "separator".
+
 - :doc:`Pre-compiled binaries <binary>` with all bundled dependencies for Linux
   (:iss:`595`)
 
-- A :doc:`new kitten <kittens/panel>` to create dock panels on X11 desktops showing the output from
-  arbitrary terminal programs.
+- A :doc:`new kitten <kittens/panel>` to create dock panels on X11 desktops
+  showing the output from arbitrary terminal programs.
 
 - Reduce data sent to the GPU per render by 30% (:commit:`8dea5b3`)
 
 - Implement changing the font size for individual top level (OS) windows
   (:iss:`408`)
 
-- ssh kitten: Support all SSH options. It can now be aliased directly to ssh for convenience. (:pull:`591`)
+- ssh kitten: Support all SSH options. It can now be aliased directly to ssh
+  for convenience. (:pull:`591`)
 
 - icat kitten: Add :option:`kitty +kitten icat --print-window-size` to easily
   detect the window size in pixels from scripting languages (:iss:`581`)

kitty/conf/utils.py

@@ -43,6 +43,18 @@ def python_string(text):
     return ast.literal_eval("'''" + text.replace("'''", "'\\''") + "'''")
 
 
+def choices(*choices):
+    defval = choices[0]
+    choices = frozenset(choices)
+
+    def choice(x):
+        x = x.lower()
+        if x not in choices:
+            x = defval
+        return x
+    return choice
+
+
 def parse_line(line, type_map, special_handling, ans, all_keys, base_path_for_includes):
     line = line.strip()
     if not line or line.startswith('#'):

kitty/config_data.py

@@ -8,14 +8,13 @@ from gettext import gettext as _
 from . import fast_data_types as defines
 from .conf.definition import option_func
 from .conf.utils import (
-    positive_float, positive_int, to_cmdline, to_color, unit_float
+    choices, positive_float, positive_int, to_cmdline, to_color, unit_float
 )
 from .fast_data_types import CURSOR_BEAM, CURSOR_BLOCK, CURSOR_UNDERLINE
 from .layout import all_layouts
 from .rgb import color_as_int, color_as_sharp, color_from_int
 from .utils import log_error
 
-
 MINIMUM_FONT_SIZE = 4
 
 
@@ -490,8 +489,27 @@ Which edge to show the tab bar on, top or bottom'''))
 o('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)'''))
 
+o('tab_bar_style', 'fade', option_type=choices('fade', 'separator'), long_text=_('''
+The tab bar style, can be one of: :code:`fade` or :code:`separator`. In the fade style,
+each tab's edges fade into the background color, in the separator style, tabs are
+separated by a configurable separator.
+'''))
+
+
+def tab_fade(x):
+    return tuple(map(unit_float, x.split()))
+
+
+o('tab_fade', '0.25 0.5 0.75 1', option_type=tab_fade, long_text=_('''
+Control how each tab fades into the background when using :code:`fade` for the
+:opt:`tab_bar_style`. Each number is an alpha (between zero and one) that controls
+how much the corresponding cell fades into the background, with zero being no fade
+and one being full fade. You can change the number of cells used by adding/removing
+entries to this list.
+'''))
+
 o('tab_separator', '"{}"'.format(default_tab_separator), option_type=tab_separator, long_text=_('''
-The separator between tabs in the tab bar'''))
+The separator between tabs in the tab bar when using :code:`separator` as the :opt:`tab_bar_style`.'''))
 
 o('active_tab_foreground', '#000', option_type=to_color, long_text=_('''
 Tab bar colors and styles'''))

kitty/rgb.py

@@ -8,6 +8,18 @@ from collections import namedtuple
 Color = namedtuple('Color', 'red green blue')
 
 
+def alpha_blend_channel(top_color, bottom_color, alpha):
+    return int(alpha * top_color + (1 - alpha) * bottom_color)
+
+
+def alpha_blend(top_color, bottom_color, alpha):
+    return Color(
+            alpha_blend_channel(top_color.red, bottom_color.red, alpha),
+            alpha_blend_channel(top_color.green, bottom_color.green, alpha),
+            alpha_blend_channel(top_color.blue, bottom_color.blue, alpha)
+    )
+
+
 def parse_single_color(c):
     if len(c) == 1:
         c += c

kitty/tab_bar.py

@@ -13,20 +13,29 @@ from .fast_data_types import (
 from .layout import Rect
 from .utils import color_as_int
 from .window import calculate_gl_geometry
+from .rgb import alpha_blend
 
-TabBarData = namedtuple('TabBarData', 'title is_active is_last needs_attention')
-DrawData = namedtuple('DrawData', 'leading_spaces sep trailing_spaces bell_on_tab bell_fg')
+TabBarData = namedtuple('TabBarData', 'title is_active needs_attention')
+DrawData = namedtuple('DrawData', 'leading_spaces sep trailing_spaces bell_on_tab bell_fg alpha active_bg inactive_bg default_bg')
 
 
-def draw_tab_with_separator(draw_data, screen, tab, before, max_title_length):
-    if draw_data.leading_spaces:
-        screen.draw(' ' * draw_data.leading_spaces)
+def as_rgb(x):
+    return (x << 8) | 2
+
+
+def draw_title(draw_data, screen, tab):
     if tab.needs_attention and draw_data.bell_on_tab:
         fg = screen.cursor.fg
         screen.cursor.fg = draw_data.bell_fg
         screen.draw('🔔 ')
         screen.cursor.fg = fg
     screen.draw(tab.title)
+
+
+def draw_tab_with_separator(draw_data, screen, tab, before, max_title_length):
+    if draw_data.leading_spaces:
+        screen.draw(' ' * draw_data.leading_spaces)
+    draw_title(draw_data, screen, tab)
     if draw_data.trailing_spaces:
         screen.draw(' ' * draw_data.trailing_spaces)
     extra = screen.cursor.x - before - max_title_length
@@ -40,6 +49,33 @@ def draw_tab_with_separator(draw_data, screen, tab, before, max_title_length):
     return end
 
 
+def draw_tab_with_fade(draw_data, screen, tab, before, max_title_length):
+    tab_bg = draw_data.active_bg if tab.is_active else draw_data.inactive_bg
+    fade_colors = [as_rgb(color_as_int(alpha_blend(tab_bg, draw_data.default_bg, alpha))) for alpha in draw_data.alpha]
+    for bg in fade_colors:
+        screen.cursor.bg = bg
+        screen.draw(' ')
+    draw_title(draw_data, screen, tab)
+    extra = screen.cursor.x - before - max_title_length
+    if extra > 0:
+        screen.cursor.x = before
+        draw_title(draw_data, screen, tab)
+        extra = screen.cursor.x - before - max_title_length
+        if extra > 0:
+            screen.cursor.x -= extra + 1
+            screen.draw('…')
+    for bg in reversed(fade_colors):
+        if extra >= 0:
+            break
+        extra += 1
+        screen.cursor.bg = bg
+        screen.draw(' ')
+    end = screen.cursor.x
+    screen.cursor.bg = as_rgb(color_as_int(draw_data.default_bg))
+    screen.draw(' ')
+    return end
+
+
 class TabBar:
 
     def __init__(self, os_window_id, opts):
@@ -70,13 +106,15 @@ class TabBar:
         self.active_font_style = opts.active_tab_font_style
         self.inactive_font_style = opts.inactive_tab_font_style
 
-        def as_rgb(x):
-            return (x << 8) | 2
-
         self.active_bg = as_rgb(color_as_int(opts.active_tab_background))
         self.active_fg = as_rgb(color_as_int(opts.active_tab_foreground))
         self.bell_fg = as_rgb(0xff0000)
-        self.draw_data = DrawData(self.leading_spaces, self.sep, self.trailing_spaces, self.opts.bell_on_tab, self.bell_fg)
+        self.draw_data = DrawData(
+            self.leading_spaces, self.sep, self.trailing_spaces, self.opts.bell_on_tab, self.bell_fg,
+            self.opts.tab_fade, self.opts.active_tab_background, self.opts.inactive_tab_background,
+            self.opts.background
+        )
+        self.draw_func = draw_tab_with_separator if self.opts.tab_bar_style == 'separator' else draw_tab_with_fade
 
     def patch_colors(self, spec):
         if 'active_tab_foreground' in spec:
@@ -117,15 +155,16 @@ class TabBar:
         s.erase_in_line(2, False)
         max_title_length = (self.screen_geometry.xnum // max(1, len(data))) - 1
         cr = []
+        last_tab = data[-1] if data else None
 
         for t in data:
             s.cursor.bg = self.active_bg if t.is_active else 0
             s.cursor.fg = self.active_fg if t.is_active else 0
             s.cursor.bold, s.cursor.italic = self.active_font_style if t.is_active else self.inactive_font_style
             before = s.cursor.x
-            end = draw_tab_with_separator(self, s, t, before, max_title_length)
+            end = self.draw_func(self.draw_data, s, t, before, max_title_length)
             cr.append((before, end))
-            if s.cursor.x > s.columns - max_title_length and not t.is_last:
+            if s.cursor.x > s.columns - max_title_length and t is not last_tab:
                 s.draw('…')
                 break
         s.erase_in_line(0, False)  # Ensure no long titles bleed after the last tab

kitty/tabs.py

@@ -473,7 +473,7 @@ class TabManager:  # {{{
                 if w.needs_attention:
                     needs_attention = True
                     break
-            ans.append(TabBarData(title, t is at, t is self.tabs[-1], needs_attention))
+            ans.append(TabBarData(title, t is at, needs_attention))
         return ans
 
     def activate_tab_at(self, x):