MEP22: Toolbar rewrite#



Branches and Pull requests#

Previous work:

Pull Requests:


The main goal of this MEP is to make it easier to modify (add, change, remove) the way the user interacts with the figures.

The user interaction with the figure is deeply integrated within the Canvas and Toolbar. Making extremely difficult to do any modification.

This MEP proposes the separation of this interaction into Toolbar, Navigation and Tools to provide independent access and reconfiguration.

This approach will make easier to create and share tools among users. In the far future, we can even foresee a kind of Marketplace for Tools where the most popular can be added into the main distribution.

Detailed description#

The reconfiguration of the Toolbar is complex, most of the time it requires a custom backend.

The creation of custom Tools sometimes interferes with the Toolbar, as example see matplotlib/matplotlib#2694 also the shortcuts are hardcoded and again not easily modifiable matplotlib/matplotlib#2699

The proposed solution is to take the actions out of the Toolbar and the shortcuts out of the Canvas. The actions and shortcuts will be in the form of Tools.

A new class Navigation will be the bridge between the events from the Canvas and Toolbar and redirect them to the appropriate Tool.

At the end the user interaction will be divided into three classes:

  • NavigationBase: This class is instantiated for each FigureManager and connect the all user interactions with the Tools

  • ToolbarBase: This existing class is relegated only as a GUI access to Tools.

  • ToolBase: Is the basic definition of Tools.



Tools can have a graphical representation as the SubplotTool or not even be present in the Toolbar as Quit.

The ToolBase has the following class attributes for configuration at definition time

  • keymap = None: Key(s) to be used to trigger the tool

  • description = '': Small description of the tool

  • image = None: Image that is used in the toolbar

The following instance attributes are set at instantiation:

  • name

  • navigation


  • trigger(self, event): This is the main method of the Tool, it is called when the Tool is triggered by:

    • Toolbar button click

    • keypress associated with the Tool Keymap

    • Call to navigation.trigger_tool(name)

  • set_figure(self, figure): Set the figure and navigation attributes

  • destroy(self, *args): Destroy the Tool graphical interface (if exists)

Available Tools#

  • ToolQuit

  • ToolEnableAllNavigation

  • ToolEnableNavigation

  • ToolToggleGrid

  • ToolToggleFullScreen

  • ToolToggleYScale

  • ToolToggleXScale

  • ToolHome

  • ToolBack

  • ToolForward

  • SaveFigureBase

  • ConfigureSubplotsBase


The ToolToggleBase has the following class attributes for configuration at definition time

  • radio_group = None: Attribute to group 'radio' like tools (mutually exclusive)

  • cursor = None: Cursor to use when the tool is active

The Toggleable Tools, can capture keypress, mouse moves, and mouse button press


  • enable(self, event): Called by ToolToggleBase.trigger method

  • disable(self, event): Called when the tool is untoggled

  • toggled: Property True or False

Available Tools#

  • ToolZoom

  • ToolPan


Methods (for backend implementation)#

  • add_toolitem(self, name, group, position, image, description, toggle): Add a toolitem to the toolbar. This method is a callback from tool_added_event (emitted by navigation)

  • set_message(self, s): Display a message on toolbar or in status bar

  • toggle_toolitem(self, name): Toggle the toolitem without firing event.

  • remove_toolitem(self, name): Remove a toolitem from the Toolbar

Backward compatibility#

For backward compatibility added 'navigation' to the list of values supported by rcParams["toolbar"] (default: 'toolbar2'), that is used for Navigation classes instantiation instead of the NavigationToolbar classes

With this parameter, it makes it transparent to anyone using the existing backends.

[@pelson comment: This also gives us an opportunity to avoid needing to implement all of this in the same PR - some backends can potentially exist without the new functionality for a short while (but it must be done at some point).]