[Octave-bug-tracker] [bug #59076] subplot replaces previously created axes

[Markus Mützel]

Update of bug #59076 (project octave):

                Severity:              3 - Normal => 2 - Minor              
                Priority:              5 - Normal => 3 - Low                
              Item Group:                    None => Feature Request        
                  Status:                    None => Confirmed              
                 Release:                  6.0.90 => dev                    
        Operating System:       Microsoft Windows => Any                    
                 Summary: subplot clears the plot => subplot replaces
previously created axes

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Follow-up Comment #1:

Confirmed here.

Something leads to the positions of the existing axes and the axes that
"subplot" wants to create not matching. That means that the following action
(from the doc) is executed:
> Any previously existing axes that would be (partly) covered by the newly
created axes are deleted. 
The difference is only very minor. And I agree that the old axes should
probably be reused.
There have been a bunch of similar bug reports in the past.

If I run your code in Matlab R2020a, the axes are reused (instead of
replaced).
I see that the figure has the following user appdata:

>> getappdata(gcf)

ans = 

  struct with fields:

    SubplotDefaultAxesLocation: [0.1300 0.1100 0.7750 0.8150]
              SubplotListeners: []
       SubplotListenersManager: [1×1
matlab.graphics.internal.SubplotListenersManager]
                  SubplotDirty: []
                   SubplotGrid: [2×1 Axes]


The two axes handles in "SubplotGrid" correspond to the two axes in the
subplot.

AFAICS, Octave tries to recognize subplot axes "from scratch" each time it is
called. It doesn't keep track of which axes are part of a "subplot" layout.
Maybe doing something similar in Octave would make it easier for "subplot" to
recognize axes it could re-use (instead of replace).

In the meantime, you could call "subplot" with the handle to the existing axes
(like you already wrote).

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  <https://savannah.gnu.org/bugs/?59076>

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