Nikolaj - I don't understand your saxsgui function. You pass in a variable number of arguments but don't try to use anything and instead reference something called gui. How was this passed in to your function? This same function also returns (has an output parameter) hgui but this is never initialized. What is this for? Perhaps show how you call saxsgui from your main code.
As for the zoomon_click callback, the two input parameters are not the handles structure or the gui (?) but the handle to the source/object that caused the callback to fire (so the object that the callback is attached to) and some event data (if any exists). The signature should look more like
function zoomon_click(hObject, eventdata)
If you wish to pass additional parameters to this function (like the figure or GUI handle), then you would do this when you assign the callback
gui.rth_axes.ButtonDownFcn = {@zoomon_click, hGui};
and youd callback signature would become
function zoomon_click(hObject, eventdata, hGui)
The trick will be to pass the GUI handle into your saxsgui function...
