--- a/scripts/plot/clabel.m	Mon Sep 23 17:57:53 2013 -0400
+++ b/scripts/plot/clabel.m	Tue Sep 24 13:16:50 2013 -0700
@@ -61,11 +61,11 @@
 ## @seealso{contour, contourf, contour3, meshc, surfc, text}
 ## @end deftypefn
 
-function retval = clabel (c, varargin)
+function h = clabel (c, varargin)
 
-  label_spacing = 2 * 72;
   have_hg = false;
   have_labelspacing = false;
+  label_spacing = 144;  # 2 inches in points
 
   if (nargin < 1)
     print_usage ();
@@ -75,12 +75,13 @@
     arg = varargin{1};
     if (isscalar (arg) && ishandle (arg)
         && strcmp (get (arg, "type"), "hggroup"))
-      obj = get (arg);
-      if (! isfield (obj, "contourmatrix"))
-        error ("clabel: expecting the handle to be a contour group");
-      endif
+      try
+        get (arg, "contourmatrix");
+      catch
+        error ("clabel: H must be a handle to a contour group");
+      end_try_catch
+      have_hg = true;
       hg = arg;
-      have_hg = true;
       varargin(1) = [];
     else
       hparent = gca ();
@@ -94,44 +95,43 @@
     v = [];
   endif
 
-  for i = 1 : length (varargin) - 1
-    arg = varargin{i};
-    if (strcmpi (arg, "labelspacing"))
-      label_spacing = varargin{i+1};
-      have_labelspacing = true;
-      varargin(i:i+1) = [];
-      break;
-    endif
-  endfor
+  idx = strcmpi (varargin(1:2:end), "manual");
+  if (any (idx))
+    error ('clabel: "manual" contour mode is not supported');
+  endif
 
-  for i = 1 : length (varargin)
-    arg = varargin{i};
-    if (strcmpi (arg, "manual"))
-      error ("clabel: manual contouring mode not supported");
-    endif
-  endfor
+  idx = find (strcmpi (varargin(1:2:end), "labelspacing"), 1);
+  if (! isempty (idx))
+    have_labelspacing = true;
+    label_spacing = varargin{2*idx};
+    varargin(2*idx+(-1:0)) = [];
+  endif    
 
   if (have_hg)
     if (! isempty (v))
       if (have_labelspacing)
         set (hg, "textlistmode", "manual", "textlist", v,
-             "labelspacing", label_spacing, "showtext", "on");
+                 "labelspacing", label_spacing, "showtext", "on");
       else
         set (hg, "textlistmode", "manual", "textlist", v, "showtext", "on");
       endif
     else
       if (have_labelspacing)
-        set (hg,"showtext", "on", "labelspacing", label_spacing);
+        set (hg, "showtext", "on", "labelspacing", label_spacing);
       else
-        set (hg,"showtext", "on");
+        set (hg, "showtext", "on");
       endif
     endif
-    retval = findobj (hg, "type", "text");
+    htmp = findobj (hg, "type", "text");
     if (! isempty (varargin))
-      set (retval, varargin {:});
+      set (htmp, varargin{:});
     endif
   else
-    retval =  __clabel__ (c, v, hparent, label_spacing, [], varargin{:});
+    htmp =  __clabel__ (c, v, hparent, label_spacing, [], varargin{:});
+  endif
+
+  if (nargout > 0)
+    h = htmp;
   endif
 
 endfunction

--- a/scripts/plot/private/__clabel__.m	Mon Sep 23 17:57:53 2013 -0400
+++ b/scripts/plot/private/__clabel__.m	Tue Sep 24 13:16:50 2013 -0700
@@ -23,11 +23,14 @@
 
 function h = __clabel__ (c, v, hparent, label_spacing, z, varargin)
 
-  ## FIXME: Why assume?  Can get position in points directly from axis.
-  ## Assume that the plot size is 4 by 3 inches.
+  hax = ancestor (hparent, "axes");
+  units = get (hax, "units");
+  set (hax, "units", "points");
+  axpos = get (hax, "position");
+  set (hax, "units", units);
   lims = axis ();
-  xspacing = 72 * 4 / abs (lims(1) - lims(2));
-  yspacing = 72 * 3 / abs (lims(3) - lims(4));
+  xspacing = axpos(3) / (lims(2) - lims (1));
+  yspacing = axpos(4) / (lims(4) - lims (3));
 
   if (isscalar (hparent) && ishandle (hparent)
       && strcmp (get (hparent, "type"), "hggroup"))
@@ -38,80 +41,89 @@
     ymin = min (y(:));
     ymax = max (y(:));
   else
-    i1 = 1;
-    while (i1 < length (c))
-      clev = c(1,i1);
-      clen = c(2,i1);
-      p = c(:, i1+1:i1+clen);
+    xmin = xmax = ymin = ymax = NaN;
+    i = 1;
+    while (i < length (c))
+      clen = c(2,i);
+      data = c(:, i+(1:clen));
 
-      xmin = min (c(1,:));
-      xmax = max (c(1,:));
-      ymin = min (c(2,:));
-      ymax = max (c(2,:));
+      xmin = min ([xmin, data(1,:)]);
+      xmax = max ([xmax, data(1,:)]);
+      ymin = min ([ymin, data(2,:)]);
+      ymax = max ([ymax, data(2,:)]);
 
-      i1 += clen+1;
+      i += clen+1;
     endwhile
   endif
 
   ## Decode contourc output format and place labels.
-  i1 = 1;
   h = [];
-  while (i1 < length (c))
-    clev = c(1,i1);
-    clen = c(2,i1);
+  i = 1;
+  while (i < length (c))
+    clev = c(1,i);
+    clen = c(2,i);
 
-    if (!isempty (v) && ! any (find (clev == v)))
-      i1 += clen+1;
+    if (! isempty (v) && ! any (v == clev))
+      i += clen+1;
       continue;
     endif
 
-    p = c(:, i1+1:i1+clen) .* repmat ([xspacing; yspacing], 1, clen);
+    p = bsxfun (@times, c(:, i+(1:clen)), [xspacing; yspacing]);
     d = sqrt (sumsq (diff (p, 1, 2)));
     cumd = cumsum (d);
-    td = sum (d);
+    td = cumd(end);
     ntag = ceil (td / label_spacing);
 
-    if (all (c(:,i1+1) == c(:,i1+clen)))
-      Spacing = td / ntag;
-      pos = Spacing / 2 + [0:ntag-1] * Spacing;
+    if (all (c(:,i+1) == c(:,i+clen)))
+      ## Closed contour
+      ## FIXME: This spreads the tags uniformly around the contour which
+      ## looks nice, but it does not respect the label_spacing attribute.
+      ## Should we follow user input, which can result in two labels being
+      ## quite close to each other?
+      spacing = td / ntag;
+      pos = spacing/2 + spacing*[0:ntag-1];
     else
+      ## Open contour
       pos = zeros (1, ntag);
-      pos(1) = (td - label_spacing * (ntag - 1)) ./ 2;
-      pos(2:ntag) = pos(1) + [1:ntag-1] * label_spacing;
+      pos(1) = (td - label_spacing*(ntag - 1)) / 2;
+      pos(2:ntag) = pos(1) + label_spacing*[1:ntag-1];
     endif
 
-    j1 = 2;
-    tlabel = sprintf ("%g", clev);
-    for i = 1 : ntag
-      tagpos = pos(i);
+    tlabel = sprintf ("%.5g", clev);
+
+    for tagpos = pos
 
-      while (j1 < clen && cumd(j1) < tagpos)
-        j1++;
-      endwhile
-      tpos = sum (c(:,i1+j1-1:i1+j1), 2) ./ 2;
+      j = find (cumd > tagpos, 1);
+      if (isempty (j))
+        j = clen;
+      endif
+      tpos = sum (c(:,i+j-1:i+j), 2) / 2;
 
       if (   tpos(1) != xmin && tpos(1) != xmax
           && tpos(2) != ymin && tpos(2) != ymax)
-        trot = 180 / pi * atan2 (diff (c(2,i1+j1-1:i1+j1)),
-                                 diff (c(1,i1+j1-1:i1+j1)));
-
+        trot = 180 / pi * atan2 (diff (c(2,i+j-1:i+j)),
+                                 diff (c(1,i+j-1:i+j)));
+        if (abs (trot) > 90)
+          trot += 180;
+        endif
         if (ischar (z))
           ht = text (tpos(1), tpos(2), clev, tlabel, "rotation", trot,
-                     "parent", hparent, "horizontalalignment", "center",
-                     "userdata", clev, varargin{:});
-        elseif (!isempty (z))
+                     "horizontalalignment", "center", "userdata", clev,
+                     "parent", hparent, varargin{:});
+        elseif (! isempty (z))
           ht = text (tpos(1), tpos(2), z, tlabel, "rotation", trot,
-                     "parent", hparent, "horizontalalignment", "center",
-                     "userdata", clev, varargin{:});
+                     "horizontalalignment", "center", "userdata", clev,
+                     "parent", hparent, varargin{:});
         else
           ht = text (tpos(1), tpos(2), tlabel, "rotation", trot,
-                     "parent", hparent, "horizontalalignment", "center",
-                     "userdata", clev, varargin{:});
+                     "horizontalalignment", "center", "userdata", clev,
+                     "parent", hparent, varargin{:});
         endif
         h = [h; ht];
       endif
     endfor
-    i1 += clen+1;
+    i += clen+1;
   endwhile
+
 endfunction