Best practice - callback override / drag graphic elements...

Hi,

I am writing a set of short and self-contained demo scripts for didactic purposes and I need to code in some user interaction. I looked a bit around for ideas and I ended up with using callback overrides, nested functions and "shared" variables (not sure how to call them sorry, they turn cyan like globals... hf1 for instance in the example below). Is this kind of code design "ok"? Or would you rather suggest different/better ways to organize things? Is there any official documentation on all this (callback override examples, draggable graphic elements etc)? I just found here and there few sporadic user examples.

thanx! S

% Simple user interaction
%
function Simple()

    hf1 = figure(1); 
    clf;
    hf1.WindowButtonUpFcn = @stopdrag;
    xv = 2*pi*(0:0.01:1);
    yv = sin(xv);
    hpl = plot(xv,yv,'k','LineWidth',1); hold on;
    hln = line([pi pi],[-1.2,+1.2]);
    hpt = plot(pi,0,'o');
    xlabel('x');
    ylabel('sin(x)');
    axis([0 2*pi -1.2 1.2]);
    
    hln.ButtonDownFcn = @startdrag;
    
    % events
    function startdrag(src,event)
        hf1.WindowButtonMotionFcn = @move;     
    end
    function move(src,event)
        pt = get(gca, 'CurrentPoint');
        hln.XData = [1 1]*pt(1,1);
        hpt.XData = pt(1,1);
        hpt.YData = sin(pt(1,1));
    end
    function stopdrag(src,event)
        hf1.WindowButtonMotionFcn = [];  
    end

end

Answer 1

[Jan]

The code looks fine. I'd avoid gca, but use the 'Parent' property directly:

function move(src,event)
        pt = get(src.Parent, 'CurrentPoint');