| ====================================== |
| MEP27: Decouple pyplot from backends |
| ====================================== |
|
|
| .. contents:: |
| :local: |
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| Status |
| ====== |
| **Progress** |
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|
| Branches and Pull requests |
| ========================== |
| Main PR (including GTK3): |
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| + https://github.com/matplotlib/matplotlib/pull/4143 |
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| Backend specific branch diffs: |
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| + 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 |
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| 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. | |
| +-------------------------+-------------------------+-------------------------+ |
|
|
|
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| 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. |
|
|
