Variables scope issue with nested functions and callback

   I'm having an issue about variable scope in my function. (a customized ginput). I think the solution is simple, but after numerous test and research,  I'm still not able to fix it. All the algorithm seems to work. I get at the end of the ginput2 function the matrix zone I want, but the variable zone in the main function doesn't change its value, even though I use nested functions.
How can I fix it ?
Thanks
Here the code:

function zone=getzone1_2b(matrice,h2)

% Determine the points inside a polygone (zone) defined by the coordinates clicked by the user on a matrice plotted in a figure h2. zone is a matrix the same size of matrice, with zone(x,y)=1 for a point inside the polygone, zone(x,y)=0 otherwise.

zone=zeros(size(matrice)); i=1; x=[]; y=[]; ht=[];

set(h2,'WindowButtonDownFcn',@ginput2); set(h2,'WindowButtonMotionFcn',@dispcoor);

% get coordinates of the points clicked by users

function ginput2(src,eventdata)

%Left click on the mouse is used to get the user click coordinates or to erase it if it was already clicked

         if strcmp(get(src,'SelectionType'),'normal')
            cp = get(gca,'CurrentPoint');
            a=round(cp(1,1));
            b=round(cp(1,2));
            iseq=find(x==a & y==b);
            if isempty(iseq)
               x(i)=a;
               y(i)=b;
               ha(i)=plot(x(i),y(i),'o','MarkerFaceColor','k','MarkerSize',10);
               i=i+1;
            else
                x(iseq)=[];
                y(iseq)=[];
                delete(ha(iseq));
                i=i-1;
            end;
          end;

% If the right button on the mouse is pressed, stop the acquisition and determine the matrix zone

          if strcmp(get(src,'SelectionType'),'alt')
             n=length(x);
 % One point
             if n==1
                zone(x,y)=1;
             end;
% For a line
             if n==2
                if y(1)==y(2)
                   zone(min(x(1),x(2)):max(x(1),x(2)),y(1))=1;
                elseif x(1)==x(2)
                       zone(x(1),min(y(1),y(2)):max(y(1),y(2)))=1;
                else
                     p=polyfit(x,y,1);
                     p=round(p);
                     if abs(p(1))==1
                        xa=[min(x(1),x(2)):max(x(1),x(2))];
                        ya=xa*p(1)+p(2);
                        B=sub2ind(size(matrice.noeud),xa,ya);
                        zone(B)=1;
                     else
                         h = msgbox('Ligne non prise en compte','Erreur','error');
                     end;
                end;
              end;
% polygon
              if n>2
                 zone=inpolygon(matrice.i,matrice.j,x,y);
              end;
             % Stop acquisition
             set(h2,'WindowButtonDownFcn','');
             set(h2,'WindowButtonMotionFcn','');

           end;

end

 % display the coordinates of the cursor

function dispcoor(src,eventdata) delete(ht); set(src,'pointer','crosshair'); cpt = get(gca,'CurrentPoint'); xt=round(cpt(1,1)); yt=round(cpt(1,2)); ht=text(cpt(1,1),cpt(1,2),['x = ' num2str(xt) ', y = ',num2str(yt)],'BackgroundColor',[1 1 1]) ; end end