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xlim listener for zoom reset and linkaxes strange behavior

Asked by Jim Hokanson on 26 Nov 2017
Latest activity Commented on by Yair Altman on 27 Nov 2017
I've attached a 'XLim' listener to an axes object.
I had been previously using a timer due to issues with catching the events appropriately (for reasons I can't exactly remember). Now they're starting to come back to me ...
Here's some basic test code (from 2017b):
ax = gca;
plot(1:100)
L1 = addlistener(ax, 'XLim', 'PostSet', @(x,y)disp(y.AffectedObject.XLim));
When I zoom in my listener fires properly. However, when I double-click to reset the zoom (or right click and reset) no listener is fired! The 'XLim' property clearly changed but Matlab doesn't seem to care to inform me of this fact.
This seems like a bug to me. Looking at SO there is a suggestion that I listen to the zoom callback, but I'd rather not touch any callbacks since I might need 2 or more callbacks for a single axes.
Even more surprising is that by linking the axes an event is now fired on resetting the zoom. This seems to persist even if I turn the linking off.
clf
ax = gca;
plot(1:100)
L1 = addlistener(ax, 'XLim', 'PostSet', @(x,y)disp(y.AffectedObject.XLim));
linkaxes(ax,'x') %reset works as desired
linkaxes(ax,'x','off') %reset still works as desired
Questions are:
  1. How can I get a listener event for zoom reset (and pan reset) that is resistant to accidental overwriting (i.e. most likely by avoiding a single callback property)
  2. If the behavior is not a bug, why? See remark below on blog post.
  3. Why does running linkaxes fix this problem?
  4. Is there a way of accomplishing whatever the linkaxes function is doing without actually needing to modify the linkaxes behavior of the axes?
The following blog post comes to mind but it seems like a reset-zoom should trigger an event. In the linked example plotting new data that expands the x-limits doesn't throw an event. https://blogs.mathworks.com/loren/2015/12/14/axes-limits-scream-louder-i-cant-hear-you/
Update:
If you plot again the event stops getting thrown in response to resetting the zoom. ¯\_(ツ)_/¯
clf
ax = gca;
plot(1:100)
L1 = addlistener(ax, 'XLim', 'PostSet', @(x,y)disp(y.AffectedObject.XLim));
linkaxes(ax,'x')
linkaxes(ax,'x','off')
plot(1:100) %reset not working as desired

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1 Answer

Answer by Jim Hokanson on 27 Nov 2017
Edited by Jim Hokanson on 27 Nov 2017
 Accepted Answer

It turns out that there is a lot of publicly readable code behind linkaxes, or really, linkprop. After some debugging I discovered the MarkedClean event. More info on this interesting event can be found at: https://undocumentedmatlab.com/blog/undocumented-hg2-graphics-events
I now have the following code:
%Updated to point to XRuler instead of just axes_handle
%per Yair's recommendation
obj.L3 = ...
addlistener(axes_handle.XRuler,'MarkedClean',@(~,~) obj.cleanListen);
end
function cleanListen(obj)
if isequal(obj.xlim,get(obj.axes_handle,'XLim'))
return
end
obj.listenerCallback();
It seems like MarkedClean is perhaps one of the ultimate 'Always tell me about things' events.
I'm not entirely sure what the answers to my questions are, but this serves as a decent workaround for what I need.

  3 Comments

Jim - as I noted at the bottom of that article, if you're only interested in monitoring XLim, then it makes more sense to listen to the MarkedClean even on the axes' XRuler and not the entire axes. This will cause your callback to trigger only when the X-axis changes, not when something is redrawn in the current axes without changing x-axis, and not when just the y- or z-axis changes. This can be very important for performance.
Thanks Yair. I'm not familiar with XRuler but a quick search turned up this info from your site:
http://undocumentedmatlab.com/blog/customizing-axes-rulers
of course, where else? :-)

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