MEP23: Multiple Figures per GUI window

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Discussion

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Previous work - https://github.com/matplotlib/matplotlib/pull/2465 To-delete

Abstract

Add the possibility to have multiple figures grouped under the same FigureManager

Detailed description

Under the current structure, every canvas has its own window.

This is and may continue to be the desired method of operation for most use cases.

Sometimes when there are too many figures open at the same time, it is desirable to be able to group these under the same window [see](https://github.com/matplotlib/matplotlib/issues/2194).

The proposed solution modifies FigureManagerBase to contain and manage more than one canvas. The settings parameter rcParams['backend.multifigure'] control when the MultiFigure behaviour is desired.

Note

It is important to note, that the proposed solution, assumes that the [MEP22](https://github.com/matplotlib/matplotlib/wiki/Mep22) is already in place. This is simply because the actual implementation of the Toolbar makes it pretty hard to switch between canvases.

Implementation

The first implementation will be done in GTK3 using a Notebook as canvas container.

FigureManagerBase

will add the following new methods

• add_canvas: To add a canvas to an existing FigureManager object
• remove_canvas: To remove a canvas from a FigureManager object, if it is the last one, it will be destroyed
• move_canvas: To move a canvas from one FigureManager to another.
• set_canvas_title: To change the title associated with a specific canvas container
• get_canvas_title: To get the title associated with a specific canvas container
• get_active_canvas: To get the canvas that is in the foreground and is subject to the gui events. There is no set_active_canvas because the active canvas, is defined when show is called on a Canvas object.

new_figure_manager

To control which FigureManager will contain the new figures, an extra optional parameter figuremanager will be added, this parameter value will be passed to new_figure_manager_given_figure

new_figure_manager_given_figure

• If figuremanager parameter is give, this FigureManager object will be used instead of creating a new one.
• If rcParams['backend.multifigure'] == True: The last FigureManager object will be used instead of creating a new one.

NavigationBase

Modifies the NavigationBase to keep a list of canvases, directing the actions to the active one

Backward compatibility

For the MultiFigure properties to be visible, the user has to activate them directly setting rcParams['backend.multifigure'] = True

It should be backwards compatible for backends that adhere to the current FigureManagerBase structure even if they have not implemented the MultiFigure magic yet.

Alternatives

Insted of modifying the FigureManagerBase it could be possible to add a parallel class, that handles the cases where rcParams['backend.multifigure'] = True. This will warranty that there won’t be any problems with custom made backends, but also makes bigger the code, and more things to maintain.