2000-11-06  Miles Bader  <address@hidden>

	* xterm.c (x_alloc_lighter_color): Boost FACTOR for dark colors.
	(Vhighlight_color_dark_boost, Vhighlight_color_dark_boost_limit):
	New variables.
	(syms_of_xterm): Initialize new variables.
	Include <math.h>.

diff -up src/xterm.c.\~1\~ src/xterm.c
--- src/xterm.c.~1~	Tue Oct 31 09:44:48 2000
+++ src/xterm.c	Tue Nov  7 12:39:08 2000
@@ -29,6 +29,7 @@ Boston, MA 02111-1307, USA.  */
 #include <signal.h>
 
 #include <stdio.h>
+#include <math.h>
 
 #ifdef HAVE_X_WINDOWS
 
@@ -383,6 +384,10 @@ extern XrmDatabase x_load_resources P_ (
 extern Lisp_Object x_icon_type P_ ((struct frame *));
 
 
+/* Parameters used by x_alloc_lighter_color.  */
+Lisp_Object Vhighlight_color_dark_boost, Vhighlight_color_dark_boost_limit;
+
+
 /* Enumeration for overriding/changing the face to use for drawing
    glyphs in x_draw_glyphs.  */
 
@@ -3511,6 +3516,59 @@ x_alloc_lighter_color (f, display, cmap,
   color.pixel = *pixel;
   x_query_color (f, &color);
 
+  if (NUMBERP (Vhighlight_color_dark_boost))
+    /* Boost FACTOR for dark colors.  */
+    {
+      long bright, limit;
+
+      /* Use the maximum component brightness as the overall brightness
+	 (this works quite well in practice).  */
+      bright = color.red;
+      if (color.green > bright)
+	bright = color.green;
+      if (color.blue > bright)
+	bright = color.blue;
+
+      if (INTEGERP (Vhighlight_color_dark_boost_limit))
+	{
+	  limit = XINT (Vhighlight_color_dark_boost_limit);
+	  if (limit > 0xFFFF)
+	    /* Limit LIMIT to the maximum color component value.  */
+	    limit = 0xFFFF;
+	}
+      else
+	limit = 48000;		/* "grey" */
+
+      /* We only boost colors that are darker than
+	 Vhighlight_color_dark_boost_limit.  */
+      if (bright > 0 && bright < limit)
+	{
+	  double boost = XFLOATINT (Vhighlight_color_dark_boost);
+
+	  if (boost > 10)
+	    /* We arbitrarily limit BOOST to 10 to avoid problems with
+	       `pow' (as the default is 0.5, 10 is probably enough).  */
+	    boost = 10;
+
+	  if (boost > 0)
+	    {
+	      /* How far below LIMIT this color is.  */
+	      double dimness = (double)limit / bright;
+	      /* How much to change FACTOR to account for BOOST at DIMNESS.  */
+	      double adjust =
+		/* The default value of BOOST is 0.5, which can be
+		   calculated about 3 times faster using `sqrt', so
+		   optimize that case.  */
+		(boost == 0.5 ? sqrt (dimness) : pow (dimness, boost));
+
+	      if (factor >= 1)
+		factor *= adjust;
+	      else
+		factor /= adjust;
+	    }
+	}
+    }
+
   /* Change RGB values by specified FACTOR.  Avoid overflow!  */
   xassert (factor >= 0);
   new.red = min (0xffff, factor * color.red);
@@ -13887,7 +13945,35 @@ wide as that tab on the display.");
 
   staticpro (&last_mouse_motion_frame);
   last_mouse_motion_frame = Qnil;
+
+  /* Initialize parameters used by x_alloc_lighter_color.  */
+
+  DEFVAR_LISP ("highlight-color-dark-boost",
+	       &Vhighlight_color_dark_boost,
+   "How much to boost the brightness of 3d highlights for dark colors.\n\
+Nominally, highlight colors for `3d' faces are calculated by brightening\n\
+an object's color by a constant factor.  If `highlight-color-dark-boost'\n\
+is a floating point number between 0 and 1, colors darker than\n\
+`highlight-color-dark-boost-limit' have their highlight factor\n\
+increased: a value of 0 means no increase at all, and a value of 1\n\
+means that all dark colors will have a highlight with a brightness\n\
+equal to `highlight-color-dark-boost-limit'.\n\
+\n\
+Changing this value will not have an effect until a new frame is created.");
+  Vhighlight_color_dark_boost = make_float (0.5);
+
+  DEFVAR_LISP ("highlight-color-dark-boost-limit",
+	       &Vhighlight_color_dark_boost_limit,
+   "Brightness beyond which a color won't have its highlight brightness boosted.\n\
+See `highlight-color-dark-boost'.\n\
+\n\
+The `brightness' of a color, for this purpose, is defined to be the\n\
+maximum of the color's red, green, or blue components, as returned by\n\
+`color-values'.");
+  /* The default value here is set so that the default
+     menu-bar/mode-line color (grey75) will not have its highlights
+     changed at all.  */
+  Vhighlight_color_dark_boost_limit = 48000;
 }
 
 #endif /* not HAVE_X_WINDOWS */
-