Simplify canvas class control in FigureFrameWx.

Remember that the wx backends have a slightly different init order
because the canvas cannot be instantiated *before* the containing window
(a "frame" in wx parlance), so previously different wx backends
implemented different frame subclasses so that each of them can
instantiate different canvas subclasses.

Instead of doing that (and having to assign them to the private
`_frame_class` attribute, which is a problem e.g. for third-party
backends such as mplcairo), directly pass the canvas class as a
parameter to FigureFrameWx.

Author: anntzer

doc/api/next_api_changes/behavior/21983-AL.rst

@@ -0,0 +1,8 @@
+``FigureFrameWx`` constructor, subclasses, and ``get_canvas``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The ``FigureCanvasWx`` constructor gained a *canvas_class* keyword-only
+parameter which specifies the canvas class that should be used.  This
+parameter will become required in the future.  The ``get_canvas`` method,
+which was previously used to customize canvas creation, is deprecated.  The
+``FigureFrameWxAgg`` and ``FigureFrameWxCairo`` subclasses, which overrode
+``get_canvas``, are deprecated.

lib/matplotlib/backends/backend_wx.py

@@ -892,7 +892,7 @@ def _print_image(self, filetype, filename):
 
 
 class FigureFrameWx(wx.Frame):
-    def __init__(self, num, fig):
+    def __init__(self, num, fig, *, canvas_class=None):
         # On non-Windows platform, explicitly set the position - fix
         # positioning bug on some Linux platforms
         if wx.Platform == '__WXMSW__':
@@ -905,7 +905,15 @@ def __init__(self, num, fig):
         self.num = num
         _set_frame_icon(self)
 
-        self.canvas = self.get_canvas(fig)
+        # The parameter will become required after the deprecation elapses.
+        if canvas_class is not None:
+            self.canvas = canvas_class(self, -1, fig)
+        else:
+            _api.warn_deprecated(
+                "3.6", message="The canvas_class parameter will become "
+                "required after the deprecation period starting in Matplotlib "
+                "%(since)s elapses.")
+            self.canvas = self.get_canvas(fig)
         w, h = map(math.ceil, fig.bbox.size)
         self.canvas.SetInitialSize(wx.Size(w, h))
         self.canvas.SetFocus()
@@ -953,6 +961,8 @@ def _get_toolbar(self):
             toolbar = None
         return toolbar
 
+    @_api.deprecated(
+        "3.6", alternative="the canvas_class constructor parameter")
     def get_canvas(self, fig):
         return FigureCanvasWx(self, -1, fig)
 
@@ -1393,7 +1403,6 @@ def trigger(self, *args, **kwargs):
 class _BackendWx(_Backend):
     FigureCanvas = FigureCanvasWx
     FigureManager = FigureManagerWx
-    _frame_class = FigureFrameWx
 
     @classmethod
     def new_figure_manager(cls, num, *args, **kwargs):
@@ -1410,7 +1419,7 @@ def new_figure_manager(cls, num, *args, **kwargs):
 
     @classmethod
     def new_figure_manager_given_figure(cls, num, figure):
-        frame = cls._frame_class(num, figure)
+        frame = FigureFrameWx(num, figure, canvas_class=cls.FigureCanvas)
         figmgr = frame.get_figure_manager()
         if mpl.is_interactive():
             figmgr.frame.Show()

lib/matplotlib/backends/backend_wxagg.py

@@ -1,11 +1,14 @@
 import wx
 
+from .. import _api
 from .backend_agg import FigureCanvasAgg
 from .backend_wx import (
     _BackendWx, _FigureCanvasWxBase, FigureFrameWx,
     NavigationToolbar2Wx as NavigationToolbar2WxAgg)
 
 
+@_api.deprecated(
+    "3.6", alternative="FigureFrameWx(..., canvas_class=FigureCanvasWxAgg)")
 class FigureFrameWxAgg(FigureFrameWx):
     def get_canvas(self, fig):
         return FigureCanvasWxAgg(self, -1, fig)
@@ -56,4 +59,3 @@ def _rgba_to_wx_bitmap(rgba):
 @_BackendWx.export
 class _BackendWxAgg(_BackendWx):
     FigureCanvas = FigureCanvasWxAgg
-    _frame_class = FigureFrameWxAgg

lib/matplotlib/backends/backend_wxcairo.py

@@ -1,11 +1,14 @@
 import wx.lib.wxcairo as wxcairo
 
+from .. import _api
 from .backend_cairo import cairo, FigureCanvasCairo
 from .backend_wx import (
     _BackendWx, _FigureCanvasWxBase, FigureFrameWx,
     NavigationToolbar2Wx as NavigationToolbar2WxCairo)
 
 
+@_api.deprecated(
+    "3.6", alternative="FigureFrameWx(..., canvas_class=FigureCanvasWxCairo)")
 class FigureFrameWxCairo(FigureFrameWx):
     def get_canvas(self, fig):
         return FigureCanvasWxCairo(self, -1, fig)
@@ -36,4 +39,3 @@ def draw(self, drawDC=None):
 @_BackendWx.export
 class _BackendWxCairo(_BackendWx):
     FigureCanvas = FigureCanvasWxCairo
-    _frame_class = FigureFrameWxCairo