function drawbspline(action)

buttonh = findobj(gcbf,'Tag','Curvebutton');

switch(action)
case 'draw'
   makecontrol('stop');
   set(buttonh,'String','Erase curve')
   set(buttonh,'Callback','drawbspline(''erase'')')

   polyhandle = findobj(gcbf,'Tag','Bpolygon');
   set(polyhandle,'ButtonDownFcn','drawbspline(''start'')')
   pp = [get(polyhandle,'XData'); get(polyhandle,'YData')];
   % find the order and knots in UserData for this figure
   t = get(polyhandle,'UserData');
   if isempty(t)
      k=4;  % default: cubic with uniform knots, endpoint mult. 4

      t=[zeros(1,k)  1:size(pp,2)-k  (size(pp,2)-k+1)*ones(1,k)];
   else
      k=t(1);
      t = t(2:length(t));
   end
   
   yy=compcurve(k,t,pp);   % function included below
   
   axishandle = findobj(gcbf,'Tag','CurveAxes');
   axes(axishandle);

   handle = line(yy(1,:),yy(2,:),'Color','b');   
   set(handle,'Tag','Bcurve')
   set(handle,'EraseMode','xor')
   set(handle,'UserData',[k t])
   set(handle,'ButtonDownFcn','drawbspline(''start'')')
   
case 'erase'
   set(buttonh,'String','Draw B-spline curve')
   delete(findobj(gcbf,'Tag','Bcurve'))
   set(buttonh,'Callback','drawbspline(''draw'')')
   polyhandle = findobj(gcbf,'Tag','Bpolygon');
   set(polyhandle,'ButtonDownFcn','')

case 'start',
   currPt = get(gca,'CurrentPoint');
   pos =[currPt(1,1); currPt(1,2)];
   polyhandle = findobj(gcbf,'Tag','Bpolygon');
   pp = [get(polyhandle,'XData'); get(polyhandle,'YData')];
   index = find( sum(abs(pp-repmat(pos,1,length(pp)))) < 0.1);
   if  length(index)>0
      set(gcbf,'WindowButtonMotionFcn','drawbspline move')
      set(gcbf,'WindowButtonUpFcn','drawbspline stop')
      set(gcbf,'UserData',index(1))
   end
   % clear other objects in the picture
   convexprop clearweak;
   convexprop clearstrong;
   makecontrol hidebez;
% display(index);
case 'move'
   currPt = get(gca,'CurrentPoint');
   pos =[currPt(1,1); currPt(1,2)];
   polyhandle = findobj(gcbf,'Tag','Bpolygon');
   pp = [get(polyhandle,'XData'); get(polyhandle,'YData')];
   index = get(gcbf,'UserData');
   pp(:,index(1)) = pos;
   set(polyhandle,'XData',pp(1,:))
   set(polyhandle,'YData',pp(2,:))
   curvehandle = findobj(gcbf,'Tag','Bcurve');
   t = get(curvehandle,'UserData');
      k=t(1);   %order
      t = t(2:length(t));  %knots
      
   yy = compcurve(k,t,pp);
   set(curvehandle,'XData',yy(1,:),'YData',yy(2,:));
   
case 'stop'
   set(gcbf,'WindowButtonMotionFcn','')
   set(gcbf,'WindowButtonUpFcn','')
   set(gcbf,'UserData',[])

end

function y=compcurve(k,t,pp)
   tmin = t(k);
   tmax = t(length(t)-k+1);

   step = (tmax-tmin)/100;

   y = bspval(t,pp,tmin:step:tmax);
%end