MEP22: Toolbar rewrite

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Status

**Progress**

Branches and Pull requests

Previous work

* https://github.com/matplotlib/matplotlib/pull/1849

* https://github.com/matplotlib/matplotlib/pull/2557

* https://github.com/matplotlib/matplotlib/pull/2465

Pull Requests:

* Removing the NavigationToolbar classes

https://github.com/matplotlib/matplotlib/pull/2740 **CLOSED**

* Keeping the NavigationToolbar classes https://github.com/matplotlib/matplotlib/pull/2759 **CLOSED**

* Navigation by events: https://github.com/matplotlib/matplotlib/pull/3652

Abstract

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 https://github.com/matplotlib/matplotlib/issues/2694 also

the shortcuts are hardcoded and again not easily modifiable

https://github.com/matplotlib/matplotlib/issues/2699

The proposed solution is to take the actions out of the `Toolbar` and

the shortcuts out of the `Canvas`. This 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 appropiate `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.

Implementation

ToolBase(object)

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

**Methods**

* 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

ToolToggleBase(ToolBase)

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

It defines the following methods

* 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

NavigationBase

Defines the following attributes

* canvas:

* keypresslock: Lock to know if the `canvas` key_press_event` is

available and process it

* messagelock: Lock to know if the message is available to write

Public methods for **User use**:

* nav_connect(self, s, func): Connect to to navigation for events

* nav_disconnect(self, cid): Disconnect from navigation event

* message_event(self, message, sender=None): Emit a

tool_message_event event

* active_toggle(self): **Property** The currently toggled tools or

None

* get_tool_keymap(self, name): Return a list of keys that are

associated with the tool

* set_tool_keymap(self, name, *keys): Set the keys for the given tool

* tools(self) **Property**: Return a dict with available tools with

corresponding keymaps, descriptions and objects

* get_tool(self, name): Return the tool object

ToolbarBase

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` (emited 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 a 'navigation' key to

`rcsetup.validate_toolbar`, 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).]

MEP22