ginput and sliders/slider callback

Hi there! I have written a code to produce a fern leaf fractal...which is great but I'd like it to be able to zoom in! My goal is to create a slider function that zooms in on a particular point (that is picked by the users mouse), then use the slider to zoom in or out on the particular point.

At this point I would even be happy having it just be able to zoom with the slider.

I have googled, looked at other code, to no avail.

I know I need to create a slider_cb but I'm not even too sure as to how it relates and what it is trying to call.

Anyone think they can help??

Here is where I am at so far...

function main()

shg

clf reset

set(gcf,'color','white','menubar','none', ...
   'numbertitle','off','name','Fractal Fern');

a=-3;
b=3;
c=0;
d=10;

x = [.5; .5];

kh = plot(x(1),x(2),'.');

treegreen = [3/5 2/3 1/8];

set(kh,'markersize',1,'color',treegreen,'erasemode','none');

axis([a b c d]);

axis off

%stop button with random color....oooh fancy
stop = uicontrol('style','toggle','string','stop', ...
   'background',rand(1,3));

drawnow

h  = [ .85  .92  .99  1.00];
A1 = [ .85  .04; -.04  .85];  b1 = [0; 1.6];
A2 = [ .20 -.26;  .23  .22];  b2 = [0; 1.6];
A3 = [-.15  .28;  .26  .24];  b3 = [0; .44];
A4 = [  0    0 ;   0   .16];

%sets count
cnt = 1;

%create the fractal
%here we use elseif statements to plot points

start_slider(1)
while ~get(stop,'value');
   r = rand;
   if r < h(1);
      x = A1*x + b1;
   elseif r < h(2);
      x = A2*x + b2;
   elseif r < h(3);
      x = A3*x + b3;
   else
      x = A4*x;
   end
   set(kh,'xdata',x(1),'ydata',x(2));
   drawnow
   cnt = cnt + 1;

end

%stop then close
set(stop,'style','pushbutton','string','close','callback','close (gcf)')

end

%
%START SLIDER
%

function start_slider(fignum)

smin = 0;
smax = 10;
slider_step = [(smax-smin)/100 0.1];
s0 = 0;

h = uicontrol(fignum,'style','Slider','Value',s0);
set(h,'Min',smin,'Max',smax,'position',[50 8 500 20]);
set(h,'Callback',@slider_cb);
set(h,'sliderstep',slider_step);   %Default : [0.01 0.1];

set(h,'Value',s0);
% slider_cb(h,[]);

lh = addlistener(h,'ContinuousValueChange',@slider_cb);
while(waitforbuttonpress)
    % This will continuously update the plot as the slider is moved.
end

end

function slider_cb(slider_handle,event_data)

val = get(slider_handle,'Value');
fprintf('value = %12.4f\n',val);

end