Store updated tab bar edge colors on every tab bar redraw

kitty/fast_data_types.pyi

@@ -1497,3 +1497,4 @@ def make_x11_window_a_dock_window(x11_window_id: int, strut: Tuple[int, int, int
 def unicode_database_version() -> Tuple[int, int, int]: ...
 def wrapped_kitten_names() -> List[str]: ...
 def expand_ansi_c_escapes(test: str) -> str: ...
+def update_tab_bar_edge_colors(os_window_id: int) -> bool: ...

kitty/screen.c

@@ -3972,11 +3972,11 @@ effective_cell_edge_color(char_type ch, color_type fg, color_type bg, bool is_le
     END_ALLOW_CASE_RANGE
 }
 
-static PyObject*
-line_edge_colors(Screen *self, PyObject *a UNUSED) {
+bool
+get_line_edge_colors(Screen *self, color_type *left, color_type *right) {
     // Return the color at the left and right edges of the line with the cursor on it
     Line *line = range_line_(self, self->cursor->y);
-    if (!line) { PyErr_SetString(PyExc_IndexError, "Line number out of range"); return NULL; }
+    if (!line) return false;
     color_type left_cell_fg = 0, left_cell_bg = 0, right_cell_bg = 0, right_cell_fg = 0;
     index_type cell_color_x = 0;
     char_type left_char = line_get_char(line, cell_color_x);
@@ -3984,9 +3984,16 @@ line_edge_colors(Screen *self, PyObject *a UNUSED) {
     if (line->xnum > 0) cell_color_x = line->xnum - 1;
     char_type right_char = line_get_char(line, cell_color_x);
     colors_for_cell(line, self->color_profile, &cell_color_x, &right_cell_fg, &right_cell_bg);
-    unsigned long left = effective_cell_edge_color(left_char, left_cell_fg, left_cell_bg, true);
-    unsigned long right = effective_cell_edge_color(right_char, right_cell_fg, right_cell_bg, false);
-    return Py_BuildValue("kk", left, right);
+    *left = effective_cell_edge_color(left_char, left_cell_fg, left_cell_bg, true);
+    *right = effective_cell_edge_color(right_char, right_cell_fg, right_cell_bg, false);
+    return true;
+}
+
+static PyObject*
+line_edge_colors(Screen *self, PyObject *a UNUSED) {
+    color_type left, right;
+    if (!get_line_edge_colors(self, &left, &right)) { PyErr_SetString(PyExc_IndexError, "Line number out of range"); return NULL; }
+    return Py_BuildValue("kk", (unsigned long)left, (unsigned long)right);
 }
 
 

kitty/screen.h

@@ -265,6 +265,7 @@ bool screen_detect_url(Screen *screen, unsigned int x, unsigned int y);
 int screen_cursor_at_a_shell_prompt(const Screen *);
 bool screen_fake_move_cursor_to_position(Screen *, index_type x, index_type y);
 bool screen_send_signal_for_key(Screen *, char key);
+bool get_line_edge_colors(Screen *self, color_type *left, color_type *right);
 #define DECLARE_CH_SCREEN_HANDLER(name) void screen_##name(Screen *screen);
 DECLARE_CH_SCREEN_HANDLER(bell)
 DECLARE_CH_SCREEN_HANDLER(backspace)

kitty/state.c

@@ -1124,6 +1124,17 @@ PYWRAP1(patch_global_colors) {
     Py_RETURN_NONE;
 }
 
+PYWRAP1(update_tab_bar_edge_colors) {
+    id_type os_window_id;
+    PA("K", &os_window_id);
+    WITH_OS_WINDOW(os_window_id)
+        if (os_window->tab_bar_render_data.screen) {
+            if (get_line_edge_colors(os_window->tab_bar_render_data.screen, &os_window->tab_bar_edge_color.left, &os_window->tab_bar_edge_color.right)) { Py_RETURN_TRUE; }
+        }
+    END_WITH_OS_WINDOW
+    Py_RETURN_FALSE;
+}
+
 static PyObject*
 pyset_background_image(PyObject *self UNUSED, PyObject *args) {
     const char *path;
@@ -1348,6 +1359,7 @@ static PyMethodDef module_methods[] = {
     MW(os_window_font_size, METH_VARARGS),
     MW(set_os_window_size, METH_VARARGS),
     MW(get_os_window_size, METH_VARARGS),
+    MW(update_tab_bar_edge_colors, METH_VARARGS),
     MW(set_boss, METH_O),
     MW(get_boss, METH_NOARGS),
     MW(apply_options_update, METH_NOARGS),

kitty/state.h

@@ -195,6 +195,9 @@ typedef struct {
     unsigned int active_tab, num_tabs, capacity, last_active_tab, last_num_tabs, last_active_window_id;
     bool focused_at_last_render, needs_render;
     ScreenRenderData tab_bar_render_data;
+    struct {
+        color_type left, right;
+    } tab_bar_edge_color;
     bool tab_bar_data_updated;
     bool is_focused;
     monotonic_t cursor_blink_zero_time, last_mouse_activity_at;

kitty/tab_bar.py

@@ -14,7 +14,7 @@ from .config import build_ansi_color_table
 from .constants import config_dir
 from .fast_data_types import (
     DECAWM, Color, Region, Screen, cell_size_for_window, get_boss, get_options,
-    pt_to_px, set_tab_bar_render_data, viewport_for_window,
+    pt_to_px, set_tab_bar_render_data, update_tab_bar_edge_colors, viewport_for_window,
 )
 from .rgb import alpha_blend, color_as_sgr, color_from_int, to_color
 from .types import WindowGeometry, run_once
@@ -664,6 +664,7 @@ class TabBar:
         self.cell_ranges = cr
         s.erase_in_line(0, False)  # Ensure no long titles bleed after the last tab
         self.align()
+        update_tab_bar_edge_colors(self.os_window_id)
 
     def align_with_factor(self, factor: int = 1) -> None:
         if not self.cell_ranges: