--- a/scripts/plot/appearance/whitebg.m	Thu Oct 27 13:17:07 2016 -0400
+++ b/scripts/plot/appearance/whitebg.m	Thu Oct 27 10:41:31 2016 -0700
@@ -20,31 +20,55 @@
 ## @deftypefn  {} {} whitebg ()
 ## @deftypefnx {} {} whitebg (@var{color})
 ## @deftypefnx {} {} whitebg ("none")
-## @deftypefnx {} {} whitebg (@var{hfig}, @dots{})
+## @deftypefnx {} {} whitebg (@var{hfig})
+## @deftypefnx {} {} whitebg (@var{hfig}, @var{color})
+## @deftypefnx {} {} whitebg (@var{hfig}, "none")
 ## Invert the colors in the current color scheme.
 ##
-## The root properties are also inverted such that all subsequent plot use the
-## new color scheme.
+## The root properties are also inverted such that all subsequent plots will
+## use the new color scheme.
 ##
 ## If the optional argument @var{color} is present then the background color
 ## is set to @var{color} rather than inverted.  @var{color} may be a string
 ## representing one of the eight known colors or an RGB triplet.  The special
-## string argument @qcode{"none"} restores the plot to the default colors.
+## string argument @qcode{"none"} restores the plot to the factory default
+## colors.
+##
+## If the first argument @var{hfig} is a figure handle or list of figure
+## handles, then operate on these figures rather than the current figure
+## returned by @code{gcf}.  The root properties will not be changed unless 0
+## is in the list of figures.
 ##
-## If the first argument @var{hfig} is a figure handle, then operate on
-## this figure rather than the current figure returned by @code{gcf}.  The
-## root properties will not be changed.
+## Programming Note: @code{whitebg} operates by changing the color properties
+## of the children of the specified figures.  Only objects with a single color
+## are affected.  For example, a patch with a single @qcode{"FaceColor"} will
+## be changed, but a patch with shading (@qcode{"interp"}) will not be
+## modified.  For inversion, the new color is simply the inversion in RGB
+## space: @code{@var{cnew} = [1-@var{R} 1-@var{G} 1-@var{B}]}.  When a color
+## is specified, the axes and figure are set to the new color, and the color
+## of child objects are then adjusted to have some contrast (visibility)
+## against the new background.
 ## @seealso{reset, get, set}
 ## @end deftypefn
 
+## FIXME: It's not clear whether Matlab also changes color properties
+## of the figure object itself, or only the children.  However, visually,
+## it looks better to change the figure along with the axes background.
+
 function whitebg (varargin)
 
+  if (nargin > 2)
+    print_usage ();
+  endif
+
   h = 0;
   color = NaN;
+  have_fig = false;
 
-  if (nargin > 0 && nargin < 3)
-    if (ishandle (varargin{1}))
+  if (nargin > 0)
+    if (all (ishandle (varargin{1})))
       h = varargin{1};
+      have_fig = true;
       if (nargin == 2)
         color = varargin{2};
       endif
@@ -53,117 +77,175 @@
     else
       print_usage ();
     endif
-  elseif (nargin != 0)
-    print_usage ();
   endif
 
-  typ = get (h, "type");
-
-  if (strcmp (typ, "root"))
-    isroot = true;
+  if (! have_fig)
     fig = gcf ();
-  elseif (strcmp (typ, "figure"))
-    isroot = false;
-    fig = h;
+    do_root = true;
+  elseif (all (isfigure (h) | h == 0))
+    fig = h(h != 0);
+    do_root = any (h == 0);
   else
-    error ("whitebg: HFIF must be a valid figure handle");
+    error ("whitebg: HFIG must be a valid figure handle");
   endif
 
-  axes = findall (fig, "type", "axes");
   if (isnan (color))
-    ## Root figure.  Set the default axes and figure properties so that
-    ## subsequent plots have the new color scheme.
-    if (isroot)
+    if (do_root)
+      ## Set the default axes and figure properties on root
+      ## so that subsequent plots have the new color scheme
       fac = get (0, "factory");
       fields = fieldnames (fac);
-      fieldindex = intersect (find (! cellfun ("isempty", regexp (fields, 'color'))), union (find (! cellfun ("isempty", regexp (fields, 'factoryaxes.*'))), find (! cellfun ("isempty", regexp (fields, 'factoryfigure.*')))));
+      idx = ! cellfun ("isempty", regexp (fields,
+                                          '^factory(axes|figure).*color$'));
 
-      ## Check whether the factory value has been replaced
-      for nf = 1 : numel (fieldindex);
-        defaultfield = strrep (fields{fieldindex(nf)}, "factory", "default");
+      ## Use default value in place of factory value if specified.
+      for field = fields(idx)'
+        defaultfield = strrep (field{1}, "factory", "default");
         try
-          defaultvalue = 1 - get (0, defaultfield{n});
+          defaultvalue = 1 - get (0, defaultfield);
         catch
-          field = fields{fieldindex(nf)};
-          defaultvalue = 1 - subsref (fac, struct ("type", ".", "subs", field));
+          defaultvalue = 1 - fac.(field{1});
         end_try_catch
         set (0, defaultfield, defaultvalue);
       endfor
     endif
 
-    ## Load all objects which qualify for being searched.
-    handles = fig;
-    h = fig;
-    while (numel (handles))
-      children = [];
-      for n = 1 : numel (handles)
-        children = union (children, get (handles(n), "children"));
-      endfor
-      handles = children;
-      h = union (h, children);
-    endwhile
+    ## The sort is necessary so that child legend objects are acted on
+    ## before the legend axes object.
+    hlist = sort (findobj (fig));
 
-    for nh = 1 : numel (h)
-      p = get (h (nh));
-      fields = fieldnames (p);
-      fieldindex = find (! cellfun ("isempty", regexp (fields, 'color')));
-      if (numel (fieldindex))
-        for nf = 1 : numel (fieldindex);
-          field = fields{fieldindex(nf)};
-          c = subsref (p, struct ("type", ".", "subs", field));
-          if (! ischar (c) && columns (c) == 3)
-            set (h (nh), field, 1 - c);
-          endif
-        endfor
+    for h = hlist'
+      props = get (h);
+      fields = fieldnames (props);
+      ## Find all fields with the word color in them and invert.
+      idx = find (! cellfun ("isempty", regexp (fields, 'color$')));
+      for field = fields(idx)';
+        c = props.(field{1});
+        if (! ischar (c) && columns (c) == 3)
+          set (h, field{1}, 1 - c);
+        endif
+      endfor
+    endfor
+
+  else  # 2nd argument such as a color or "none"
+
+    if (! strcmp (color, "none"))
+      ## Set the specified color on the figure and all axes objects
+      hlist = [fig; findobj(fig, "type", "axes")];
+      set (hlist, "color", color);
+      if (do_root)
+        defs = get (0, "default");
+        if (isfield (defs, "defaultaxescolor")
+            && strcmp (defs.defaultaxescolor, "none"))
+          set (0, "defaultaxescolor", color);
+        endif
       endif
 
-      ## If h(nh) is a figure or axes invert default color properties
-      typ = subsref (p, struct ("type", ".", "subs", "type"));
-      if (strcmp (typ, "axes") || strcmp (typ, "figure"))
-        def = get (h (nh), "default");
-        fields = fieldnames (def);
-        if (! isempty (fields))
-          fieldindex = find (! cellfun ("isempty", regexp (fields, 'color')));
-          for nf = 1 : numel (fieldindex)
-            defaultfield = fields{fieldindex(nf)};
-            defaultvalue = ...
-              1 - subsref (def, struct ("type", ".", "subs", defaultfield));
-            set (h (nh), defaultfield, defaultvalue);
-          endfor
-        endif
+      ## Adjust colors of remaining objects to have some contrast
+      bg = rgb2hsv (get (fig, "color"));
+      ## List of children without the figure and axes objects already changed
+      hlist = setdiff (findobj (fig), hlist);
+      for h = hlist'
+        props = get (h);
+        fields = fieldnames (props);
+        ## Find all fields with the word color in them and adjust HSV.
+        idx = find (! cellfun ("isempty", regexp (fields, 'color$')));
+        for field = fields(idx)';
+          c = props.(field{1});
+          if (! ischar (c) && columns (c) == 3)
+            set (h, field{1}, calc_contrast_color (bg, c));
+          endif
+        endfor
+      endfor
+
+    else
+      ## Reset colors to factory defaults
+      if (do_root)
+        fac = get (0, "factory");
+        fields = fieldnames (fac);
+        idx = ! cellfun ("isempty", regexp (fields,
+                                            '^factory(axes|figure).*color$'));
+        for field = fields(idx)'
+          factoryfield = field{1};
+          factoryvalue = fac.(factoryfield);
+          if (strncmp (factoryfield, "factoryfigure", 13))
+            ## Strip off "factoryfigure" part of fieldname before applying
+            set (fig, factoryfield(14:end), factoryvalue);
+          endif
+          ## Remove applied default from root
+          defaultfield = strrep (factoryfield, "factory", "default");
+          set (0, defaultfield, "remove");
+        endfor 
       endif
-    endfor
-  else
-    ## FIXME: Is this the right thing to do in this case?
-    set (findall (fig, "type", "axes"), "color", color);
-    if (isroot)
-      defs = get (0, "default");
-      if (isfield (defs, "defaultaxescolor")
-          && strcmp (defs.defaultaxescolor, "none"))
-        set (0, "defaultaxescolor", color);
-      endif
+
+      hlist = sort (findobj (fig));
+      for h = hlist'
+        props = get (h);
+        fields = fieldnames (props);
+        ## Find all fields with the word color in them and restore to factory.
+        idx = find (! cellfun ("isempty", regexp (fields, 'color$')));
+        for field = fields(idx)'
+          set (h, field{1}, "factory");
+        endfor
+      endfor
     endif
   endif
 
 endfunction
 
+## Calculate a new color which contrasts with the supplied bg color and is
+## perceptually related to the original color.
+##
+## Input color bg must be in HSV space.  Input color corig is in RGB space.
+##
+## FIXME: Calculation is segregated into its own function in case anyone wants
+## to try and improve the selection of a "contrasting" color.
+##
+## This algorithm maintains at least 90 degrees separation between corig and bg
+## in Hue rotation space.  No modifications are done for saturation or value.
+function cnew = calc_contrast_color (bg, corig)
+  
+  hsv = rgb2hsv (corig);
+  contrast_hue = mod (bg(1) + 0.5, 1);  # Generate a contrasting bg color
+
+  ## If close to existing contrast color, leave alone
+  delta = abs (hsv(1) - contrast_hue);
+  if (delta < 0.25 || delta > 0.75)
+    cnew(1) = hsv(1);
+  else
+    cnew(1) = mod (hsv(1) + 0.5, 1);
+  endif
+
+  ## No modifications to saturation or value.
+  cnew(2:3) = hsv(2:3);
+
+  cnew = hsv2rgb (cnew);   
+
+endfunction
+
 
 %!test
 %! dac = get (0, "defaultaxescolor");
 %! dfc = get (0, "defaultfigurecolor");
 %! hf = figure ("visible", "off");
 %! unwind_protect
-%!   l = line;
+%!   hl = line ("Color", "r");
 %!   assert (get (hf, "color"), dfc);
 %!   assert (get (gca, "color"), dac);
+%!   assert (get (hl, "color"), [1 0 0]);
 %!   whitebg (hf);
 %!   assert (get (hf, "color"), 1 - dfc);
 %!   assert (get (gca, "color"), 1 - dac);
+%!   assert (get (hl, "color"), [0 1 1]);
 %!   c = [0.2 0.2 0.2];
 %!   whitebg (hf, c);
-%!   assert (get (hf, "color"), 1 - dfc);
+%!   assert (get (hf, "color"), c);
 %!   assert (get (gca, "color"), c);
 %! unwind_protect_cleanup
 %!   close (hf);
 %! end_unwind_protect
 
+## Test input validation
+%!error whitebg (1,2,3)
+%!error whitebg ({1}, 2)
+