3 files changed, 90 insertions, 0 deletions

diff --git a/src/w32fns.c b/src/w32fns.c
index 4b95b255f1c..0d6369461cd 100644
--- a/src/w32fns.c
+++ b/src/w32fns.c
@@ -1773,6 +1773,94 @@ w32_set_menu_bar_lines (struct frame *f, Lisp_Object value, Lisp_Object oldval)
 }
 
 
+/* Set the number of lines used for the tab bar of frame F to VALUE.
+   VALUE not an integer, or < 0 means set the lines to zero.  OLDVAL
+   is the old number of tab bar lines.  This function changes the
+   height of all windows on frame F to match the new tab bar height.
+   The frame's height doesn't change.  */
+
+static void
+w32_set_tab_bar_lines (struct frame *f, Lisp_Object value, Lisp_Object oldval)
+{
+  int nlines;
+
+  /* Treat tab bars like menu bars.  */
+  if (FRAME_MINIBUF_ONLY_P (f))
+    return;
+
+  /* Use VALUE only if an int >= 0.  */
+  if (RANGED_FIXNUMP (0, value, INT_MAX))
+    nlines = XFIXNAT (value);
+  else
+    nlines = 0;
+
+  w32_change_tab_bar_height (f, nlines * FRAME_LINE_HEIGHT (f));
+}
+
+
+/* Set the pixel height of the tab bar of frame F to HEIGHT.  */
+void
+w32_change_tab_bar_height (struct frame *f, int height)
+{
+  int unit = FRAME_LINE_HEIGHT (f);
+  int old_height = FRAME_TAB_BAR_HEIGHT (f);
+  int lines = (height + unit - 1) / unit;
+  Lisp_Object fullscreen;
+
+  /* Make sure we redisplay all windows in this frame.  */
+  fset_redisplay (f);
+
+  /* Recalculate tab bar and frame text sizes.  */
+  FRAME_TAB_BAR_HEIGHT (f) = height;
+  FRAME_TAB_BAR_LINES (f) = lines;
+  /* Store the `tab-bar-lines' and `height' frame parameters.  */
+  store_frame_param (f, Qtab_bar_lines, make_fixnum (lines));
+  store_frame_param (f, Qheight, make_fixnum (FRAME_LINES (f)));
+
+  /* We also have to make sure that the internal border at the top of
+     the frame, below the menu bar or tab bar, is redrawn when the
+     tab bar disappears.  This is so because the internal border is
+     below the tab bar if one is displayed, but is below the menu bar
+     if there isn't a tab bar.  The tab bar draws into the area
+     below the menu bar.  */
+  if (FRAME_W32_WINDOW (f) && FRAME_TAB_BAR_HEIGHT (f) == 0)
+    {
+      clear_frame (f);
+      clear_current_matrices (f);
+    }
+
+  if ((height < old_height) && WINDOWP (f->tab_bar_window))
+    clear_glyph_matrix (XWINDOW (f->tab_bar_window)->current_matrix);
+
+  /* Recalculate tabbar height.  */
+  f->n_tab_bar_rows = 0;
+  if (old_height == 0
+      && (!f->after_make_frame
+          || NILP (frame_inhibit_implied_resize)
+          || (CONSP (frame_inhibit_implied_resize)
+              && NILP (Fmemq (Qtab_bar_lines, frame_inhibit_implied_resize)))))
+    f->tab_bar_redisplayed = f->tab_bar_resized = false;
+
+  adjust_frame_size (f, -1, -1,
+                     ((!f->tab_bar_resized
+                       && (NILP (fullscreen =
+                                 get_frame_param (f, Qfullscreen))
+                           || EQ (fullscreen, Qfullwidth))) ? 1
+                      : (old_height == 0 || height == 0) ? 2
+                      : 4),
+                     false, Qtab_bar_lines);
+
+  f->tab_bar_resized = f->tab_bar_redisplayed;
+
+  /* adjust_frame_size might not have done anything, garbage frame
+     here.  */
+  adjust_frame_glyphs (f);
+  SET_FRAME_GARBAGED (f);
+  if (FRAME_W32_WINDOW (f))
+    w32_clear_under_internal_border (f);
+}
+
+
 /* Set the number of lines used for the tool bar of frame F to VALUE.
    VALUE not an integer, or < 0 means set the lines to zero.  OLDVAL is
    the old number of tool bar lines (and is unused).  This function may
diff --git a/src/w32term.c b/src/w32term.c
index 82c7e211bfd..1f57635f6db 100644
--- a/src/w32term.c
+++ b/src/w32term.c
@@ -7192,6 +7192,7 @@ w32_create_terminal (struct w32_display_info *dpyinfo)
   terminal->menu_show_hook = w32_menu_show;
   terminal->activate_menubar_hook = w32_activate_menubar;
   terminal->popup_dialog_hook = w32_popup_dialog;
+  terminal->change_tab_bar_height_hook = w32_change_tab_bar_height;
   terminal->change_tool_bar_height_hook = w32_change_tool_bar_height;
   terminal->set_vertical_scroll_bar_hook = w32_set_vertical_scroll_bar;
   terminal->set_horizontal_scroll_bar_hook = w32_set_horizontal_scroll_bar;
diff --git a/src/w32term.h b/src/w32term.h
index 6133e100c17..378f274d7ed 100644
--- a/src/w32term.h
+++ b/src/w32term.h
@@ -233,6 +233,7 @@ extern void w32_real_positions (struct frame *f, int *xptr, int *yptr);
 
 extern void w32_clear_under_internal_border (struct frame *);
 
+extern void w32_change_tab_bar_height (struct frame *, int);
 extern void w32_change_tool_bar_height (struct frame *, int);
 extern void w32_implicitly_set_name (struct frame *, Lisp_Object, Lisp_Object);
 extern void w32_set_scroll_bar_default_width (struct frame *);