--- a/scripts/plot/draw/surfnorm.m	Fri Jul 18 09:16:27 2014 -0700
+++ b/scripts/plot/draw/surfnorm.m	Sun Jul 20 13:26:10 2014 -0700
@@ -19,49 +19,56 @@
 ## -*- texinfo -*-
 ## @deftypefn  {Function File} {} surfnorm (@var{x}, @var{y}, @var{z})
 ## @deftypefnx {Function File} {} surfnorm (@var{z})
+## @deftypefnx {Function File} {} surfnorm (@dots{}, @var{prop}, @var{val}, @dots{})
+## @deftypefnx {Function File} {} surfnorm (@var{hax}, @dots{})
 ## @deftypefnx {Function File} {[@var{nx}, @var{ny}, @var{nz}] =} surfnorm (@dots{})
-## @deftypefnx {Function File} {} surfnorm (@var{h}, @dots{})
-## Find the vectors normal to a meshgridded surface.  The meshed gridded
-## surface is defined by @var{x}, @var{y}, and @var{z}.  If @var{x} and
-## @var{y} are not defined, then it is assumed that they are given by
+## Find the vectors normal to a meshgridded surface.
 ##
-## @example
-## @group
-## [@var{x}, @var{y}] = meshgrid (1:rows (@var{z}),
-##                    1:columns (@var{z}));
-## @end group
-## @end example
+## If @var{x} and @var{y} are vectors, then a typical vertex is
+## (@var{x}(j), @var{y}(i), @var{z}(i,j)).  Thus, columns of @var{z} correspond
+## to different @var{x} values and rows of @var{z} correspond to different
+## @var{y} values.  If only a single input @var{z} is given then @var{x} is
+## taken to be @code{1:rows (@var{z})} and @var{y} is
+## @code{1:columns (@var{z})}.
 ##
 ## If no return arguments are requested, a surface plot with the normal
-## vectors to the surface is plotted.  Otherwise the components of the normal
-## vectors at the mesh gridded points are returned in @var{nx}, @var{ny},
-## and @var{nz}.
+## vectors to the surface is plotted.
 ##
-## The normal vectors are calculated by taking the cross product of the
-## diagonals of each of the quadrilaterals in the meshgrid to find the
-## normal vectors of the centers of these quadrilaterals.  The four nearest
-## normal vectors to the meshgrid points are then averaged to obtain the
-## normal to the surface at the meshgridded points.
+## Any property/value input pairs are assigned to the surface object.
+## 
+## If the first argument @var{hax} is an axes handle, then plot into this axis,
+## rather than the current axes returned by @code{gca}.
+##
+## If output arguments are requested then the components of the normal
+## vectors are returne in @var{nx}, @var{ny}, and @var{nz} and no plot is
+## made.
 ##
 ## An example of the use of @code{surfnorm} is
 ##
 ## @example
 ## surfnorm (peaks (25));
 ## @end example
-## @seealso{surf, quiver3}
+##
+## Algorithm: The normal vectors are calculated by taking the cross product
+## of the diagonals of each of the quadrilaterals in the meshgrid to find the
+## normal vectors of the centers of these quadrilaterals.  The four nearest
+## normal vectors to the meshgrid points are then averaged to obtain the
+## normal to the surface at the meshgridded points.
+##
+## @seealso{isonormals, quiver3, surf, meshgrid}
 ## @end deftypefn
 
 function [Nx, Ny, Nz] = surfnorm (varargin)
 
   [hax, varargin, nargin] = __plt_get_axis_arg__ ("surfnorm", varargin{:});
 
-  if (nargin != 1 && nargin != 3)
+  if (nargin == 0 || nargin == 2)
     print_usage ();
   endif
 
   if (nargin == 1)
     z = varargin{1};
-    [x, y] = meshgrid (1:rows (z), 1:columns (z));
+    [x, y] = meshgrid (1:columns (z), 1:rows (z));
     ioff = 2;
   else
     x = varargin{1};
@@ -70,22 +77,24 @@
     ioff = 4;
   endif
 
-  if (!ismatrix (z) || isvector (z) || isscalar (z))
-    error ("surfnorm: Z argument must be a matrix");
+  if (iscomplex (z) || iscomplex (x) || iscomplex (y))
+    error ("surfnorm: X, Y, and Z must be 2-D real matrices");
   endif
   if (! size_equal (x, y, z))
     error ("surfnorm: X, Y, and Z must have the same dimensions");
   endif
 
-  ## Make life easier, and avoid having to do the extrapolation later, do
-  ## a simpler linear extrapolation here. This is approximative, and works
-  ## badly for closed surfaces like spheres.
-  xx = [2 .* x(:,1) - x(:,2), x, 2 .* x(:,end) - x(:,end-1)];
-  xx = [2 .* xx(1,:) - xx(2,:); xx; 2 .* xx(end,:) - xx(end-1,:)];
-  yy = [2 .* y(:,1) - y(:,2), y, 2 .* y(:,end) - y(:,end-1)];
-  yy = [2 .* yy(1,:) - yy(2,:); yy; 2 .* yy(end,:) - yy(end-1,:)];
-  zz = [2 .* z(:,1) - z(:,2), z, 2 .* z(:,end) - z(:,end-1)];
-  zz = [2 .* zz(1,:) - zz(2,:); zz; 2 .* zz(end,:) - zz(end-1,:)];
+  ## Do a linear extrapolation for mesh points on the boundary so that the mesh
+  ## is increased by 1 on each side.  This allows each original meshgrid point
+  ## to be surrounded by four quadrilaterals and the same calculation can be
+  ## used for interior and boundary points.  The extrapolation works badly for
+  ## closed surfaces like spheres.
+  xx = [2 * x(:,1) - x(:,2), x, 2 * x(:,end) - x(:,end-1)];
+  xx = [2 * xx(1,:) - xx(2,:); xx; 2 * xx(end,:) - xx(end-1,:)];
+  yy = [2 * y(:,1) - y(:,2), y, 2 * y(:,end) - y(:,end-1)];
+  yy = [2 * yy(1,:) - yy(2,:); yy; 2 * yy(end,:) - yy(end-1,:)];
+  zz = [2 * z(:,1) - z(:,2), z, 2 * z(:,end) - z(:,end-1)];
+  zz = [2 * zz(1,:) - zz(2,:); zz; 2 * zz(end,:) - zz(end-1,:)];
 
   u.x = xx(1:end-1,1:end-1) - xx(2:end,2:end);
   u.y = yy(1:end-1,1:end-1) - yy(2:end,2:end);
@@ -101,17 +110,19 @@
 
   ## Create normal vectors as mesh vectices from normals at mesh centers
   nx = (w.x(1:end-1,1:end-1) + w.x(1:end-1,2:end) +
-        w.x(2:end,1:end-1) + w.x(2:end,2:end)) ./ 4;
+        w.x(2:end,1:end-1) + w.x(2:end,2:end)) / 4;
   ny = (w.y(1:end-1,1:end-1) + w.y(1:end-1,2:end) +
-        w.y(2:end,1:end-1) + w.y(2:end,2:end)) ./ 4;
+        w.y(2:end,1:end-1) + w.y(2:end,2:end)) / 4;
   nz = (w.z(1:end-1,1:end-1) + w.z(1:end-1,2:end) +
-        w.z(2:end,1:end-1) + w.z(2:end,2:end)) ./ 4;
+        w.z(2:end,1:end-1) + w.z(2:end,2:end)) / 4;
 
+  ## FIXME: According to Matlab documentation the vertex normals
+  ##        returned are not normalized.
   ## Normalize the normal vectors
   len = sqrt (nx.^2 + ny.^2 + nz.^2);
-  nx = nx ./ len;
-  ny = ny ./ len;
-  nz = nz ./ len;
+  nx ./= len;
+  ny ./= len;
+  nz ./= len;
 
   if (nargout == 0)
     oldfig = [];
@@ -125,10 +136,26 @@
       old_hold_state = get (hax, "nextplot");
       unwind_protect
         set (hax, "nextplot", "add");
-        plot3 ([x(:)'; x(:).' + nx(:).' ; NaN(size(x(:).'))](:),
-               [y(:)'; y(:).' + ny(:).' ; NaN(size(y(:).'))](:),
-               [z(:)'; z(:).' + nz(:).' ; NaN(size(z(:).'))](:),
-               varargin{ioff:end});
+
+        ## FIXME: Scale unit normals by data aspect ratio in order for
+        ##        normals to appear correct.
+        ##daratio = daspect (hax);
+        ##daspect ("manual");
+        ##len = norm (daratio);
+        ## This assumes an even meshgrid which isn't a great assumption
+        ##dx = x(1,2) - x(1,1);  
+        ##dy = y(2,1) - y(1,1);  
+        ##nx *= daratio(1);
+        ##ny *= daratio(2);
+        ##nz *= daratio(3);
+        ##len = sqrt (nx.^2 + ny.^2 + nz.^2);
+        ##nx ./= len;
+        ##ny ./= len;
+        ##nz ./= len;
+        plot3 ([x(:).'; x(:).' + nx(:).' ; NaN(size(x(:).'))](:),
+               [y(:).'; y(:).' + ny(:).' ; NaN(size(y(:).'))](:),
+               [z(:).'; z(:).' + nz(:).' ; NaN(size(z(:).'))](:),
+               "r");
       unwind_protect_cleanup
         set (hax, "nextplot", old_hold_state);
       end_unwind_protect
@@ -150,17 +177,25 @@
 %!demo
 %! clf;
 %! colormap ('default');
-%! [x, y, z] = peaks (10);
-%! surfnorm (x, y, z);
+%! surfnorm (peaks (32));
+%! shading interp;
+%! title ({'surfnorm() shows surface and normals at each vertex', ...
+%!         'peaks() function with 32 faces'});
 
 %!demo
 %! clf;
 %! colormap ('default');
-%! surfnorm (peaks (10));
+%! [x, y, z] = sombrero (10);
+%! surfnorm (x, y, z);
 
-%!demo
-%! clf;
-%! colormap ('default');
-%! surfnorm (peaks (32));
-%! shading interp;
+%% Test input validation
+%!error surfnorm ()
+%!error surfnorm (1,2)
+%!error <X, Y, and Z must be 2-D real matrices> surfnorm (i)
+%!error <X, Y, and Z must be 2-D real matrices> surfnorm (i, 1, 1)
+%!error <X, Y, and Z must be 2-D real matrices> surfnorm (1, i, 1)
+%!error <X, Y, and Z must be 2-D real matrices> surfnorm (1, 1, i)
+%!error <X, Y, and Z must have the same dimensions> surfnorm ([1 2], 1, 1)
+%!error <X, Y, and Z must have the same dimensions> surfnorm (1, [1 2], 1)
+%!error <X, Y, and Z must have the same dimensions> surfnorm (1, 1, [1 2])