| ====================================== | |
| MEP27: Decouple pyplot from backends | |
| ====================================== | |
| .. contents:: | |
| :local: | |
| Status | |
| ====== | |
| **Progress** | |
| Branches and Pull requests | |
| ========================== | |
| Main PR (including GTK3): | |
| + https://github.com/matplotlib/matplotlib/pull/4143 | |
| Backend specific branch diffs: | |
| + https://github.com/OceanWolf/matplotlib/compare/backend-refactor...OceanWolf:backend-refactor-tkagg | |
| + https://github.com/OceanWolf/matplotlib/compare/backend-refactor...OceanWolf:backend-refactor-qt | |
| + https://github.com/OceanWolf/matplotlib/compare/backend-refactor...backend-refactor-wx | |
| Abstract | |
| ======== | |
| This MEP refactors the backends to give a more structured and | |
| consistent API, removing generic code and consolidate existing code. | |
| To do this we propose splitting: | |
| 1. ``FigureManagerBase`` and its derived classes into the core | |
| functionality class ``FigureManager`` and a backend specific class | |
| ``WindowBase`` and | |
| 2. ``ShowBase`` and its derived classes into ``Gcf.show_all`` and ``MainLoopBase``. | |
| Detailed description | |
| ==================== | |
| This MEP aims to consolidate the backends API into one single uniform | |
| API, removing generic code out of the backend (which includes | |
| ``_pylab_helpers`` and ``Gcf``), and push code to a more appropriate | |
| level in matplotlib. With this we automatically remove | |
| inconsistencies that appear in the backends, such as | |
| ``FigureManagerBase.resize(w, h)`` which sometimes sets the canvas, | |
| and other times set the entire window to the dimensions given, | |
| depending on the backend. | |
| Two main places for generic code appear in the classes derived from | |
| ``FigureManagerBase`` and ``ShowBase``. | |
| 1. ``FigureManagerBase`` has **three** jobs at the moment: | |
| 1. The documentation describes it as a *Helper class for pyplot | |
| mode, wraps everything up into a neat bundle* | |
| 2. But it doesn't just wrap the canvas and toolbar, it also does | |
| all of the windowing tasks itself. The conflation of these two | |
| tasks gets seen the best in the following line: | |
| ``self.set_window_title("Figure %d" % num)`` This combines | |
| backend specific code ``self.set_window_title(title)`` with | |
| matplotlib generic code ``title = "Figure %d" % num``. | |
| 3. Currently the backend specific subclass of ``FigureManager`` | |
| decides when to end the mainloop. This also seems very wrong | |
| as the figure should have no control over the other figures. | |
| 2. ``ShowBase`` has two jobs: | |
| 1. It has the job of going through all figure managers registered | |
| in ``_pylab_helpers.Gcf`` and telling them to show themselves. | |
| 2. And secondly it has the job of performing the backend specific | |
| ``mainloop`` to block the main programme and thus keep the | |
| figures from dying. | |
| Implementation | |
| ============== | |
| The description of this MEP gives us most of the solution: | |
| 1. To remove the windowing aspect out of ``FigureManagerBase`` letting | |
| it simply wrap this new class along with the other backend classes. | |
| Create a new ``WindowBase`` class that can handle this | |
| functionality, with pass-through methods (:arrow_right:) to | |
| ``WindowBase``. Classes that subclass ``WindowBase`` should also | |
| subclass the GUI specific window class to ensure backward | |
| compatibility (``manager.window == manager.window``). | |
| 2. Refactor the mainloop of ``ShowBase`` into ``MainLoopBase``, which | |
| encapsulates the end of the loop as well. We give an instance of | |
| ``MainLoop`` to ``FigureManager`` as a key unlock the exit method | |
| (requiring all keys returned before the loop can die). Note this | |
| opens the possibility for multiple backends to run concurrently. | |
| 3. Now that ``FigureManagerBase`` has no backend specifics in it, to | |
| rename it to ``FigureManager``, and move to a new file | |
| ``backend_managers.py`` noting that: | |
| 1. This allows us to break up the conversion of backends into | |
| separate PRs as we can keep the existing ``FigureManagerBase`` | |
| class and its dependencies intact. | |
| 2. And this also anticipates MEP22 where the new | |
| ``NavigationBase`` has morphed into a backend independent | |
| ``ToolManager``. | |
| +--------------------------------------+------------------------------+---------------------+--------------------------------+ | |
| |FigureManagerBase(canvas, num) |FigureManager(figure, num) |``WindowBase(title)``|Notes | | |
| | | | | | | |
| +======================================+==============================+=====================+================================+ | |
| |show | |show | | | |
| +--------------------------------------+------------------------------+---------------------+--------------------------------+ | |
| |destroy |calls destroy on all |destroy | | | |
| | |components | | | | |
| +--------------------------------------+------------------------------+---------------------+--------------------------------+ | |
| |full_screen_toggle |handles logic |set_fullscreen | | | |
| +--------------------------------------+------------------------------+---------------------+--------------------------------+ | |
| |resize | |resize | | | |
| +--------------------------------------+------------------------------+---------------------+--------------------------------+ | |
| |key_press |key_press | | | | |
| +--------------------------------------+------------------------------+---------------------+--------------------------------+ | |
| |get_window_title | |get_window_title | | | |
| +--------------------------------------+------------------------------+---------------------+--------------------------------+ | |
| |set_window_title | |set_window_title | | | |
| +--------------------------------------+------------------------------+---------------------+--------------------------------+ | |
| | |_get_toolbar | |A common method to all | | |
| | | | |subclasses of FigureManagerBase | | |
| +--------------------------------------+------------------------------+---------------------+--------------------------------+ | |
| | | |set_default_size | | | |
| +--------------------------------------+------------------------------+---------------------+--------------------------------+ | |
| | | |add_element_to_window| | | |
| +--------------------------------------+------------------------------+---------------------+--------------------------------+ | |
| +----------+------------+-------------+ | |
| |ShowBase |MainLoopBase|Notes | | |
| +==========+============+=============+ | |
| |mainloop |begin | | | |
| +----------+------------+-------------+ | |
| | |end |Gets called | | |
| | | |automagically| | |
| | | |when no more | | |
| | | |instances of | | |
| | | |the subclass | | |
| | | |exist | | |
| +----------+------------+-------------+ | |
| |__call__ | |Method moved | | |
| | | |to | | |
| | | |Gcf.show_all | | |
| +----------+------------+-------------+ | |
| Future compatibility | |
| ==================== | |
| As eluded to above when discussing MEP 22, this refactor makes it easy | |
| to add in new generic features. At the moment, MEP 22 has to make | |
| ugly hacks to each class extending from ``FigureManagerBase``. With | |
| this code, this only needs to get made in the single ``FigureManager`` | |
| class. This also makes the later deprecation of | |
| ``NavigationToolbar2`` very straightforward, only needing to touch the | |
| single ``FigureManager`` class | |
| MEP 23 makes for another use case where this refactored code will come | |
| in very handy. | |
| Backward compatibility | |
| ====================== | |
| As we leave all backend code intact, only adding missing methods to | |
| existing classes, this should work seamlessly for all use cases. The | |
| only difference will lie for backends that used | |
| ``FigureManager.resize`` to resize the canvas and not the window, due | |
| to the standardisation of the API. | |
| I would envision that the classes made obsolete by this refactor get | |
| deprecated and removed on the same timetable as | |
| ``NavigationToolbar2``, also note that the change in call signature to | |
| the ``FigureCanvasWx`` constructor, while backward compatible, I think | |
| the old (imho ugly style) signature should get deprecated and removed | |
| in the same manner as everything else. | |
| +-------------------------+-------------------------+-------------------------+ | |
| |backend |manager.resize(w,h) |Extra | | |
| +=========================+=========================+=========================+ | |
| |gtk3 |window | | | |
| +-------------------------+-------------------------+-------------------------+ | |
| |Tk |canvas | | | |
| +-------------------------+-------------------------+-------------------------+ | |
| |Qt |window | | | |
| +-------------------------+-------------------------+-------------------------+ | |
| |Wx |canvas |FigureManagerWx had | | |
| | | |``frame`` as an alias to | | |
| | | |window, so this also | | |
| | | |breaks BC. | | |
| +-------------------------+-------------------------+-------------------------+ | |
| Alternatives | |
| ============ | |
| If there were any alternative solutions to solving the same problem, | |
| they should be discussed here, along with a justification for the | |
| chosen approach. | |
| Questions | |
| ========= | |
| Mdehoon: Can you elaborate on how to run multiple backends | |
| concurrently? | |
| OceanWolf: @mdehoon, as I say, not for this MEP, but I see this MEP | |
| opens it up as a future possibility. Basically the ``MainLoopBase`` | |
| class acts a per backend Gcf, in this MEP it tracks the number of | |
| figures open per backend, and manages the mainloops for those | |
| backends. It closes the backend specific mainloop when it detects | |
| that no figures remain open for that backend. Because of this I | |
| imagine that with only a small amount of tweaking that we can do | |
| full-multi-backend matplotlib. No idea yet why one would want to, but | |
| I leave the possibility there in MainLoopBase. With all the | |
| backend-code specifics refactored out of ``FigureManager`` also aids | |
| in this, one manager to rule them (the backends) all. | |
| Mdehoon: @OceanWolf, OK, thanks for the explanation. Having a uniform | |
| API for the backends is very important for the maintainability of | |
| matplotlib. I think this MEP is a step in the right direction. | |