% This functions craetes a figure window and allows user to
% pick an arbitrary interface.
% Pressing the spacebar terminates the sequence of points.
% Parameters:
%   width and hight are the dimensions of the area,
% Returns:
%   layer is array of picked points (each row cotains x and y of picked point)

function [layer] = picklayer(width,height)

  layer = [];       % initial empty array of points

  fig = figure(1);
  
  while true        % infinite loop waiting for user inputs
      
    clf
    hold on;
    axis([0,width,0,height]);   % plot range
    set(gca,'YDir','reverse');  % reverse the vertical axis
    xlabel("Distance (m)");
    ylabel("Depth (m)");

           % plot line and nodes
    
    if size(layer,1) > 1
      plot(layer(:,1),layer(:,2),'b-');
    end
    
    if size(layer,1) > 0
      plot(layer(:,1),layer(:,2),'bo');
    end
         % read mouse position (x,y) and key ptessed by the user 
  
    [ x, y, key ] = ginput(1);   
    
          % interpret user's action

    if x < 0 || x > width || y < 0 || y > height	% outside of plot range
	break
    end
 
    switch key 
        case  32   % spacebar pressed - drop out of the loop
            break
        case 1      % left mouse button - pick a new point
              
            if isempty(layer)     % doing first point
                layer = [x,y];
            else                  % need to insert a point
                
                  % add a point at the end and then sort by X
              layer = [ layer; x, y ];      
              
              [xsort, ind] = sort(layer(:,1));
              
              layer = layer(ind,:);
            end
            
         otherwise
            continue
            
    end     % switch
 
  end   % big loop
    
  close(fig);
  
end   % function