function locklines(tagmoved,taglocked,delta,movecall,upcall)
%LOCKLINES locks two movable straight lines created with TESTLINE
%
%    Format: locklines(tagmoved,taglocked,delta,movecall,upcall)
%       -tagmoved = tag of line that is currently being moved
%       -taglocked = tag of line locked to moved line
%       -delta = x or y difference between lines to lock
%          delta='unlock' removes the movecall callback from both lines
%          delta='lock' sets the movecall callback for both lines
%       -movecall:
%            -if lines are locked, movecall is evaluated here
%            -if 'unlock' is given, userdata(4) of testlines are set to movecall
%
% Bill Miller
% Updated April 10, 2001

if nargin<3,return,end

if ~exist('movecall')
   movecall='';
end

hm=findobj('tag',tagmoved);
hl=findobj('tag',taglocked);

if (isempty(hm) | isempty(hl)),return,end

hax=get(hm,'parent');
pt=get(gca,'currentpoint');
pt=[pt(1,1) pt(1,2)];

ul=get(hl,'userdata');
um=get(hm,'userdata');

tp(1)=um{2};
tp(2)=ul{2};

if ~strcmp(tp(1),tp(2)),return,end

xposm=get(hm,'xdata');
yposm=get(hm,'ydata');
xposl=get(hl,'xdata');
yposl=get(hl,'ydata');

xlim=get(hax,'xlim');
ylim=get(hax,'ylim');

if isstr(delta)
	switch delta
   	case 'lock'
         switch tp(1)
         	case 'h'
            	delta=abs(yposm(1)-yposl(1));   
            case 'v'
               delta=abs(xposm(1)-xposl(1));
         end
         sdelta=num2str(delta);
   
      	ul{3}=['locklines(''' taglocked ''',''' tagmoved ''',' sdelta ');'];
   	   um{3}=['locklines(''' tagmoved ''',''' taglocked ''',' sdelta ');'];
         set(hl,'userdata',ul)
         set(hm,'userdata',um)

      case 'unlock'
	      ul{3}=movecall;
   	   um{3}=movecall;
         set(hl,'userdata',ul)
         set(hm,'userdata',um)
      otherwise
   end
   return   
end

%delta is a number


switch tp(1)
	case 'h'
      postype='ydata';
      
      if yposl(1)<yposm(1)
         
         if (pt(2)-delta)<ylim(1)
            pos=yposl+delta;
		      poshnd=hm;
         else
            pos=yposm-delta;
		      poshnd=hl;
         end
         
      else
         if (pt(2)+delta)>ylim(2)
            pos=yposl-delta;
		      poshnd=hm;
         else
            pos=yposm+delta;
 		      poshnd=hl;
        end
      end
            
   case 'v'
      postype='xdata';

   	if xposl(1)<xposm(1)
         
         if (pt(1)-delta)<xlim(1)
            pos=xposl+delta;
		      poshnd=hm;
         else
         	pos=xposm-delta;
  		      poshnd=hl;
         end
      else
         
         if (pt(1)+delta)>xlim(2)
            pos=xposl-delta;
		      poshnd=hm;
         else
            pos=xposm+delta;
            poshnd=hl;
         end
      end
end      


wbmf=get(gcf,'WindowButtonMotionFcn');
set(gcf,'WindowButtonMotionFcn','');
drawnow

set(poshnd,postype,pos)
   
set(gcf,'WindowButtonMotionFcn',wbmf);

drawnow

%evaluate movecall
eval(movecall)