Undocumented HG2 graphics events

14 Responses to Undocumented HG2 graphics events

1. Yaroslav says:

   May 28, 2015 at 1:21 am

   The HG2 axes events became hidden in version R2015a. In my R2014b they are visible:

   >> events(gca)
   Events for class matlab.graphics.axis.Axes:
       LocationChanged
       SizeChanged
       ClaReset
       ClaPreReset
       Cla
       ObjectBeingDestroyed
       Hit
       LegendableObjectsUpdated
       MarkedDirty
       MarkedClean
       Error
       Reparent
       Reset
       PropertyAdded
       PropertyRemoved

   I recall making use of the Hit event on several occasions. IMHO, it is the most useful event in the list. Can’t see why TMW decided to hide it in the latest release.

   The only hidden events in R2014b are PreUpdate and PostUpdate, which have a protected Observable value:

   >> mc = metaclass(gca);
   >> [{mc.EventList.Name}; ...
       {mc.EventList.ListenAccess}; ...
       arrayfun(@mat2str, [mc.EventList.Hidden], 'Uniform',false)]'
   ans = 
       'LocationChanged'             'public'       'false'
       'SizeChanged'                 'public'       'false'
       'ClaReset'                    'public'       'false'
       'ClaPreReset'                 'public'       'false'
       'Cla'                         'public'       'false'
       'ObjectBeingDestroyed'        'public'       'false'
       'Hit'                         'public'       'false'
       'LegendableObjectsUpdated'    'public'       'false'
       'MarkedDirty'                 'public'       'false'
       'MarkedClean'                 'public'       'false'
       'PreUpdate'                   'protected'    'false'
       'PostUpdate'                  'protected'    'false'
       'Error'                       'public'       'false'
       'Reparent'                    'public'       'false'
       'Reset'                       'public'       'false'
       'PropertyAdded'               'public'       'false'
       'PropertyRemoved'             'public'       'false'

   Reply
   • Yair Altman says:

     May 28, 2015 at 1:25 am

     @Yaroslav – thanks. It would be useful to hear how and why you’ve used the Hit event.
   • Yaroslav says:

     May 28, 2015 at 1:56 am

     @Yair — let’s examine a minimal working example:

     ax=axes('NextPlot','add');
     addlistener(ax,'Hit',@(obj,evd)plot(evd.IntersectionPoint(1),evd.IntersectionPoint(2),'ob'));

     It plots a point on the axes each time it is hit. One could argue that the ButtonDownFcn property does the same thing. Yet, upon closer inspection, under the hood ButtonDownFcn uses Hit to operate:

     ax.ButtonDownFcn = @(obj,evd)display(evd);

     <Clicks on the axes>

     evd = 
      
       Hit with properties:
      
                    Button: 1
         IntersectionPoint: [0.4223 0.3771 0]
                    Source: [1x1 Axes]
                 EventName: 'Hit'

     If one needs only a single callback, I guess that ButtonDownFcn will suffice. If there is a necessity for more than one, Hit is invaluable.
   • Thomas says:

     September 14, 2016 at 10:52 am

     Hey thanks, i will use ‘Hit’!
2. Vlad Atanasiu says:

   May 31, 2015 at 7:18 am

   Hello Yair,

   You contributed to this discussion https://www.mathworks.com/matlabcentral/newsreader/view_thread/283529 on how to change event listening of such toolbar objects as zoom or pan. The solution consisted in using

   set(hManager.WindowListenerHandles,'Enable','off');

   FYI it appears however that in R2014b modifying WindowListenerHandles is not possible: its SetAccess property is set to protected. Additionally, the former property Enable, a string ( ‘on’ | ‘off’ ), is now called Enabled and has become a scalar ( 0|1 ). Try:

   hManager = uigetmodemanager(gcf);
   mc = metaclass(hManager)
   mc.PropertyList(5)

   Thanks, Vlad

   Reply
   • Yair Altman says:

     May 31, 2015 at 7:55 am

     @Vlad – that post is 5 years old and used undocumented/unsupported functionality. What’s surprising is not that it finally broke in R2014b, but that it kept working for so long. You can’t expect undocumented/unsupported functionality to keep working forever.

     Specifically, R2014b broke quite a lot of undocumented features in its change of the graphics system (HG2). In most cases, things that broke have similarly-undocumented (or documented) equivalents in HG2, you just need to dig around a bit to discover them. The hard part was discovering the initial undocumented features in HG1; finding their equivalents in HG2 should be much easier.

     Good luck!
3. Daniel says:

   June 2, 2015 at 2:42 am

   While it seems like you can prevent re-entry with

   persistent inCallback
   if ~isempty(inCallback),  return;  end
   inCallback = 1;  % disable callback re-entrancy

   since MATLAB timers run asynchronously and can execute between any two lines of code, if a timer callback occurs between the check and setting of inCallback, then you can get re-entry if the timer callback either calls reformatTickLabels or flushes the event queue and reformatTickLabels is in the event queue. I think to be safe you would need to do the check and setting of inCallback atomically, possibly with a mex file.

   Reply
   • Yair Altman says:

     June 2, 2015 at 3:53 am

     @Daniel – I agree that an atomic (mutexed) test-and-set function would be better, although in practice the probability of reentrancy with the above code is low. If you create such a MEX-based function and post it on the Matlab File Exchange , I’ll be happy to reference it in this blog.
4. Nick says:

   November 2, 2016 at 11:40 pm

   I’ve been trying to find a way to prevent our users from deleting axes when they are deleting annotations. (This happens way more than I expected, and it is a major source of frustration). I thought it’d be easy to find an event or callback to hook into and pop up a dialog, but it’s proven fairly difficult for me to crack.

   I thought maybe I could set a listener for ObjectBeingDestroyed, but it fires after the object is gone (or there’s a synch issue).

   Is there some kind of ObjectAboutToBeDestroyed or DestroyObjectRequest thats double-secret-undocumented?

   Any thoughts as to how I can hook into this behavior (or as a welcomed alternative, turn off the ability to delete axes with the keyboard – I mean seriously, why is that even a thing?)

   function testAxesDelete
       hs = struct('fig', figure);
       hs.fig.MenuBar = 'none';
       hs.fig.ToolBar = 'figure';
       hs.fig.KeyPressFcn = @myKeyCallback;
    
       hs.ax = axes;
       hs.line = plot([0 0], [-1 1]);
    
       hs.ax.DeleteFcn = @myDeleteCallback;
       hs.ax.ButtonDownFcn = @myButtonCallback;
    
       addlistener(hs.ax, 'ObjectBeingDestroyed', @obdCallback);    
   end
    
   function myKeyCallback(hobj, event, varargin)
       disp('Pressed a key on figure!');
       disp('Axes still is deleted if you press delete with the axis selected');
       disp('Axis is deleted prior to executing this function')
       keyboard
   end
    
   function myDeleteCallback(hobj, event, varargin)
       disp('Deleting axes!');
       disp('Axis is deleted prior to executing this function')
       keyboard
   end
    
   function myButtonCallback(hobj, event, varargin)
       disp('Does not intercept delete key');
       keyboard
   end
    
   function obdCallback(hobj, event, varargin)
       disp('Object being destroyed callback');
       disp('this happens *after* the axes have been deleted ');
       keyboard
   end

   Reply
   • Yair Altman says:

     November 3, 2016 at 8:57 am

     @Nick –

     set(gca,'HitTest','off')
   • Nick says:

     November 3, 2016 at 3:25 pm

     You are my hero – thank you for this invaluable resource. And thank you for pointing me to an (embarrassed) *documented* feature.

     Cheers!
   • Nick says:

     November 3, 2016 at 6:48 pm

     I just learned a fun fact: plotting to an axes object who’s HitTest property is set to ‘off’ appears to reset HitTest to ‘on’
   • Yair Altman says:

     November 3, 2016 at 7:07 pm

     @Nick – this is a “known” undocumented side-effect of using the high-level plotting functions (such as plot), which reset several axes properties including HitTest and Tag. In contrast, the low-level plotting functions (such as line) do not reset these properties.
   • Nick says:

     November 3, 2016 at 8:05 pm

     Yair – It looks like setting the Axes ‘NextPlot’ property to ‘add’ may prevent the resetting of HitTest. There is more behavior to investigate, but at least I seem to be on some kind of path. Thank you again