% grads_colormap -- generates a grads 2 colormap from a matlab colormap
%
% Copyright (C) 2010-2011 Samuel G Trahan
% 
% This program is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
% 
% This program is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU General Public License for more details.
% 
% You should have received a copy of the GNU General Public License
% along with this program.  If not, see <http://www.gnu.org/licenses/>.

function [txt]=grads_colormap(N,cm,cax)
% txt=grads_colormap(N,cm,cax)
%
% Generates a grads 2.0 script that will reproduce a matlab
% colormap and color axis limit.
%
%   N -- optional.  The number of colors to place in the grads
%     colormap.  If missing, then min(240,size(cm,1)) will be
%     used.
%
%   cm -- optional.  The matlab colormap as an Nx3 array of real
%     numbers from 0 to 1.  If missing, colormap() will be used.
%
%   cax -- optional.  Color axis limit; the first and last data
%     values to use in contour plotting.  If missing, caxis()
%     will be used.
%
% NOTE: grads has a limit of 240 colors for contour plots, so this
% routine will abort if N>240.  Also, N must be at least 3.
%

  if(nargin<3)
    cax=caxis();
    if(nargin<2)
      cm=colormap();
    end   
  end

  nc=size(cm,1);
  if(nc<2)
    error(['This function requires at least 2 colors in the ' ...
           'colormap.'])
  end
  if(numel(cax)~=2 || ~isreal(cax))
    error('cax must be a two-argument real vector');
  end
  if(any(cm<0 | cm>1 | ~isreal(cm)))
    error(['There are invalid values in your colomap.  It must contain ' ...
           'only real numbers from 0 to 1.']);
  end

  if(nargin<1)
    N=min(240,nc);
  else
    if(N>240 || N<3)
      error('N must be between 3 and 240, inclusive.')
    end
  end

  if(N~=nc)
    cm=interp1(1:nc,cm,linspace(1,nc,N));
  end

  cax=sort(cax);
  c=floor(round(cm*255));

  txt='';
  for i=1:size(cm,1)
    txt=[txt,sprintf('''set rgb %d %d %d %d''\n',...
                i+15,c(i,1),c(i,2),c(i,3))];
  end
  txt=[txt,sprintf('\n')];
  txt=[txt,'''set clevs ',num2str(linspace(cax(1),cax(2),N-1)),sprintf('''\n')];
  txt=[txt,'''set ccols ',num2str(15+(1:N)),sprintf('''\n')];
  txt=[txt,sprintf('''set gxout shaded''\n')];

end