Index: src/xterm.c
===================================================================
RCS file: /sources/emacs/emacs/src/xterm.c,v
retrieving revision 1.993
diff -U 4 -r1.993 xterm.c
--- src/xterm.c	25 May 2008 11:14:31 -0000	1.993
+++ src/xterm.c	26 May 2008 00:09:27 -0000
@@ -182,8 +182,14 @@
 /* Non-zero means to draw the underline at the same place as the descent line.  */
 
 int x_underline_at_descent_line;
 
+/* Require underline to be at least this many screen pixels below baseline
+   This to avoid underline "merging" with the base of letters at small
+   font sizes, particularly when x_use_underline_position_properties is on. */
+
+int x_underline_minimum_display_offset;
+
 /* This is a chain of structures for all the X displays currently in
    use.  */
 
 struct x_display_info *x_display_list;
@@ -2741,8 +2747,10 @@
 		    position = s->font->underline_position;
 		  else if (s->font)
 		    position = (s->font->descent + 1) / 2;
 		}
+	      if (x_underline_minimum_display_offset)
+		position = max (position, eabs (x_underline_minimum_display_offset));
 	    }
 	  /* Check the sanity of thickness and position.  We should
 	     avoid drawing underline out of the current line area.  */
 	  if (s->y + s->height <= s->ybase + position)
@@ -10782,9 +10790,11 @@
 	       &x_use_underline_position_properties,
      doc: /* *Non-nil means make use of UNDERLINE_POSITION font properties.
 A value of nil means ignore them.  If you encounter fonts with bogus
 UNDERLINE_POSITION font properties, for example 7x13 on XFree prior
-to 4.1, set this to nil.  */);
+to 4.1, set this to nil. Variable `x-underline-minimum-display-offset' may
+be used to override the font's UNDERLINE_POSITION for small font display
+sizes. */);
   x_use_underline_position_properties = 1;
 
   DEFVAR_BOOL ("x-underline-at-descent-line",
 	       &x_underline_at_descent_line,
@@ -10793,8 +10803,18 @@
 variable `x-use-underline-position-properties', which is usually at the
 baseline level.  The default value is nil.  */);
   x_underline_at_descent_line = 0;
 
+  DEFVAR_INT ("x-underline-minimum-display-offset",
+	       &x_underline_minimum_display_offset,
+     doc: /* *When > 0, underline is drawn at least that many screen pixels below baseline.
+This can improve legibility of underlined text at small font sizes,
+particularly when using variable `x-use-underline-position-properties'
+with fonts that specify an UNDERLINE_POSITION relatively close to the
+baseline. The default value is 0. */);
+  x_underline_minimum_display_offset = 0;
+
+
   DEFVAR_BOOL ("x-mouse-click-focus-ignore-position",
 	       &x_mouse_click_focus_ignore_position,
     doc: /* Non-nil means that a mouse click to focus a frame does not move point.
 This variable is only used when the window manager requires that you
Index: lisp/cus-start.el
===================================================================
RCS file: /sources/emacs/emacs/lisp/cus-start.el,v
retrieving revision 1.122
diff -U 4 -r1.122 cus-start.el
--- lisp/cus-start.el	6 May 2008 07:57:29 -0000	1.122
+++ lisp/cus-start.el	26 May 2008 00:09:27 -0000
@@ -392,8 +392,9 @@
 	     (x-gtk-whole-detached-tool-bar x boolean "22.1")
 	     ;; xterm.c
 	     (x-use-underline-position-properties display boolean "22.1")
 	     (x-underline-at-descent-line display boolean "22.1")
+	     (x-underline-minimum-display-offset display integer "23.1")
 	     (x-stretch-cursor display boolean "21.1")))
       this symbol group type standard version native-p
       ;; This function turns a value
       ;; into an expression which produces that value.