matplotlib · jklymak · Feb 5, 2018 · Jan 10, 2018 · Feb 4, 2018 · Feb 4, 2018
diff --git a/doc/api/backend_qt4cairo_api.rst b/doc/api/backend_qt4cairo_api.rst
@@ -0,0 +1,8 @@
+
+:mod:`matplotlib.backends.backend_qt4cairo`
+===========================================
+
+.. automodule:: matplotlib.backends.backend_qt4cairo
+   :members:
+   :undoc-members:
+   :show-inheritance:
diff --git a/doc/api/backend_qt5cairo_api.rst b/doc/api/backend_qt5cairo_api.rst
@@ -0,0 +1,8 @@
+
+:mod:`matplotlib.backends.backend_qt5cairo`
+===========================================
+
+.. automodule:: matplotlib.backends.backend_qt5cairo
+   :members:
+   :undoc-members:
+   :show-inheritance:
diff --git a/doc/api/index_backend_api.rst b/doc/api/index_backend_api.rst
@@ -19,7 +19,9 @@ backends
    backend_pgf_api.rst
    backend_ps_api.rst
    backend_qt4agg_api.rst
+   backend_qt4cairo_api.rst
    backend_qt5agg_api.rst
+   backend_qt5cairo_api.rst
    backend_svg_api.rst
    backend_tkagg_api.rst
    backend_webagg_api.rst

diff --git a/doc/users/next_whats_new/more-cairo.rst b/doc/users/next_whats_new/more-cairo.rst
@@ -0,0 +1,5 @@
+Cairo rendering for Qt canvases
+-------------------------------
+
+The new ``Qt4Cairo`` and ``Qt5Cairo`` backends allow Qt canvases to use Cairo
+rendering instead of Agg.
diff --git a/lib/matplotlib/backends/backend_agg.py b/lib/matplotlib/backends/backend_agg.py
@@ -429,6 +429,9 @@ def draw(self):
             # if toolbar:
             #     toolbar.set_cursor(cursors.WAIT)
             self.figure.draw(self.renderer)
+            # A GUI class may be need to update a window using this draw, so
+            # don't forget to call the superclass.
+            super(FigureCanvasAgg, self).draw()
         finally:
             # if toolbar:
             #     toolbar.set_cursor(toolbar._lastCursor)

diff --git a/lib/matplotlib/backends/backend_qt4cairo.py b/lib/matplotlib/backends/backend_qt4cairo.py
@@ -0,0 +1,6 @@
+from .backend_qt5cairo import _BackendQT5Cairo
+
+
+@_BackendQT5Cairo.export
+class _BackendQT4Cairo(_BackendQT5Cairo):
+    pass
diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
@@ -8,6 +8,7 @@
 import signal
 import sys
 from six import unichr
+import traceback
 
 import matplotlib
 
@@ -226,19 +227,16 @@ class FigureCanvasQT(QtWidgets.QWidget, FigureCanvasBase):
                # QtCore.Qt.XButton2: None,
                }
 
-    def _update_figure_dpi(self):
-        dpi = self._dpi_ratio * self.figure._original_dpi
-        self.figure._set_dpi(dpi, forward=False)
-
     @_allow_super_init
     def __init__(self, figure):
         _create_qApp()
         super(FigureCanvasQT, self).__init__(figure=figure)
 
-        figure._original_dpi = figure.dpi
         self.figure = figure
+        # We don't want to scale up the figure DPI more than once.
+        # Note, we don't handle a signal for changing DPI yet.
+        figure._original_dpi = figure.dpi
         self._update_figure_dpi()
-        self.resize(*self.get_width_height())
         # In cases with mixed resolution displays, we need to be careful if the
         # dpi_ratio changes - in this case we need to resize the canvas
         # accordingly. We could watch for screenChanged events from Qt, but
@@ -248,13 +246,23 @@ def __init__(self, figure):
         # needed.
         self._dpi_ratio_prev = None
 
+        self._draw_pending = False
+        self._is_drawing = False
+        self._draw_rect_callback = lambda painter: None
+
+        self.setAttribute(QtCore.Qt.WA_OpaquePaintEvent)
         self.setMouseTracking(True)
+        self.resize(*self.get_width_height())
         # Key auto-repeat enabled by default
         self._keyautorepeat = True
 
         palette = QtGui.QPalette(QtCore.Qt.white)
         self.setPalette(palette)
 
+    def _update_figure_dpi(self):
+        dpi = self._dpi_ratio * self.figure._original_dpi
+        self.figure._set_dpi(dpi, forward=False)
+
     @property
     def _dpi_ratio(self):
         # Not available on Qt4 or some older Qt5.
@@ -263,6 +271,26 @@ def _dpi_ratio(self):
         except AttributeError:
             return 1
 
+    def _update_dpi(self):
+        # As described in __init__ above, we need to be careful in cases with
+        # mixed resolution displays if dpi_ratio is changing between painting
+        # events.
+        # Return whether we triggered a resizeEvent (and thus a paintEvent)
+        # from within this function.
+        if self._dpi_ratio != self._dpi_ratio_prev:
+            # We need to update the figure DPI.
+            self._update_figure_dpi()
+            self._dpi_ratio_prev = self._dpi_ratio
+            # The easiest way to resize the canvas is to emit a resizeEvent
+            # since we implement all the logic for resizing the canvas for
+            # that event.
+            event = QtGui.QResizeEvent(self.size(), self.size())
+            self.resizeEvent(event)
+            # resizeEvent triggers a paintEvent itself, so we exit this one
+            # (after making sure that the event is immediately handled).
+            return True
+        return False
+
     def get_width_height(self):
         w, h = FigureCanvasBase.get_width_height(self)
         return int(w / self._dpi_ratio), int(h / self._dpi_ratio)
@@ -453,6 +481,60 @@ def stop_event_loop(self, event=None):
         if hasattr(self, "_event_loop"):
             self._event_loop.quit()
 
+    def draw(self):
+        """Render the figure, and queue a request for a Qt draw.
+        """
+        # The renderer draw is done here; delaying causes problems with code
+        # that uses the result of the draw() to update plot elements.
+        if self._is_drawing:
+            return
+        self._is_drawing = True
+        try:
+            super(FigureCanvasQT, self).draw()
+        finally:
+            self._is_drawing = False
+        self.update()
+
+    def draw_idle(self):
+        """Queue redraw of the Agg buffer and request Qt paintEvent.
+        """
+        # The Agg draw needs to be handled by the same thread matplotlib
+        # modifies the scene graph from. Post Agg draw request to the
+        # current event loop in order to ensure thread affinity and to
+        # accumulate multiple draw requests from event handling.
+        # TODO: queued signal connection might be safer than singleShot
+        if not (self._draw_pending or self._is_drawing):
+            self._draw_pending = True
+            QtCore.QTimer.singleShot(0, self._draw_idle)
+
+    def _draw_idle(self):
+        if self.height() < 0 or self.width() < 0:
+            self._draw_pending = False
+        if not self._draw_pending:
+            return
+        try:
+            self.draw()
+        except Exception:
+            # Uncaught exceptions are fatal for PyQt5, so catch them instead.
+            traceback.print_exc()
+        finally:
+            self._draw_pending = False
+
+    def drawRectangle(self, rect):
+        # Draw the zoom rectangle to the QPainter.  _draw_rect_callback needs
+        # to be called at the end of paintEvent.
+        if rect is not None:
+            def _draw_rect_callback(painter):
+                pen = QtGui.QPen(QtCore.Qt.black, 1 / self._dpi_ratio,
+                                 QtCore.Qt.DotLine)
+                painter.setPen(pen)
+                painter.drawRect(*(pt / self._dpi_ratio for pt in rect))
+        else:
+            def _draw_rect_callback(painter):
+                return
+        self._draw_rect_callback = _draw_rect_callback
+        self.update()
+
 
 class MainWindow(QtWidgets.QMainWindow):
     closing = QtCore.Signal()

diff --git a/lib/matplotlib/backends/backend_qt5agg.py b/lib/matplotlib/backends/backend_qt5agg.py
@@ -7,7 +7,6 @@
 import six
 
 import ctypes
-import traceback
 
 from matplotlib import cbook
 from matplotlib.transforms import Bbox
@@ -19,32 +18,11 @@
 from .qt_compat import QT_API
 
 
-class FigureCanvasQTAggBase(FigureCanvasAgg):
-    """
-    The canvas the figure renders into.  Calls the draw and print fig
-    methods, creates the renderers, etc...
-
-    Attributes
-    ----------
-    figure : `matplotlib.figure.Figure`
-        A high-level Figure instance
-
-    """
+class FigureCanvasQTAgg(FigureCanvasAgg, FigureCanvasQT):
 
     def __init__(self, figure):
-        super(FigureCanvasQTAggBase, self).__init__(figure=figure)
-        self.setAttribute(QtCore.Qt.WA_OpaquePaintEvent)
-        self._agg_draw_pending = False
-        self._agg_is_drawing = False
+        super(FigureCanvasQTAgg, self).__init__(figure=figure)
         self._bbox_queue = []
-        self._drawRect = None
-
-    def drawRectangle(self, rect):
-        if rect is not None:
-            self._drawRect = [pt / self._dpi_ratio for pt in rect]
-        else:
-            self._drawRect = None
-        self.update()
 
     @property
     @cbook.deprecated("2.1")
@@ -57,27 +35,10 @@ def paintEvent(self, e):
         In Qt, all drawing should be done inside of here when a widget is
         shown onscreen.
         """
-        # if there is a pending draw, run it now as we need the updated render
-        # to paint the widget
-        if self._agg_draw_pending:
-            self.__draw_idle_agg()
-        # As described in __init__ above, we need to be careful in cases with
-        # mixed resolution displays if dpi_ratio is changing between painting
-        # events.
-        if self._dpi_ratio != self._dpi_ratio_prev:
-            # We need to update the figure DPI
-            self._update_figure_dpi()
-            self._dpi_ratio_prev = self._dpi_ratio
-            # The easiest way to resize the canvas is to emit a resizeEvent
-            # since we implement all the logic for resizing the canvas for
-            # that event.
-            event = QtGui.QResizeEvent(self.size(), self.size())
-            # We use self.resizeEvent here instead of QApplication.postEvent
-            # since the latter doesn't guarantee that the event will be emitted
-            # straight away, and this causes visual delays in the changes.
-            self.resizeEvent(event)
-            # resizeEvent triggers a paintEvent itself, so we exit this one.
+        if self._update_dpi():
+            # The dpi update triggered its own paintEvent.
             return
+        self._draw_idle()  # Only does something if a draw is pending.
 
         # if the canvas does not have a renderer, then give up and wait for
         # FigureCanvasAgg.draw(self) to be called
@@ -100,72 +61,20 @@ def paintEvent(self, e):
             reg = self.copy_from_bbox(bbox)
             buf = reg.to_string_argb()
             qimage = QtGui.QImage(buf, w, h, QtGui.QImage.Format_ARGB32)
+            # Adjust the buf reference count to work around a memory leak bug
+            # in QImage under PySide on Python 3.
+            if QT_API == 'PySide' and six.PY3:
+                ctypes.c_long.from_address(id(buf)).value = 1
             if hasattr(qimage, 'setDevicePixelRatio'):
                 # Not available on Qt4 or some older Qt5.
                 qimage.setDevicePixelRatio(self._dpi_ratio)
             origin = QtCore.QPoint(l, self.renderer.height - t)
             painter.drawImage(origin / self._dpi_ratio, qimage)
-            # Adjust the buf reference count to work around a memory
-            # leak bug in QImage under PySide on Python 3.
-            if QT_API == 'PySide' and six.PY3:
-                ctypes.c_long.from_address(id(buf)).value = 1
 
-        # draw the zoom rectangle to the QPainter
-        if self._drawRect is not None:
-            pen = QtGui.QPen(QtCore.Qt.black, 1 / self._dpi_ratio,
-                             QtCore.Qt.DotLine)
-            painter.setPen(pen)
-            x, y, w, h = self._drawRect
-            painter.drawRect(x, y, w, h)
+        self._draw_rect_callback(painter)
 
         painter.end()
 
-    def draw(self):
-        """Draw the figure with Agg, and queue a request for a Qt draw.
-        """
-        # The Agg draw is done here; delaying causes problems with code that
-        # uses the result of the draw() to update plot elements.
-        if self._agg_is_drawing:
-            return
-
-        self._agg_is_drawing = True
-        try:
-            super(FigureCanvasQTAggBase, self).draw()
-        finally:
-            self._agg_is_drawing = False
-        self.update()
-
-    def draw_idle(self):
-        """Queue redraw of the Agg buffer and request Qt paintEvent.
-        """
-        # The Agg draw needs to be handled by the same thread matplotlib
-        # modifies the scene graph from. Post Agg draw request to the
-        # current event loop in order to ensure thread affinity and to
-        # accumulate multiple draw requests from event handling.
-        # TODO: queued signal connection might be safer than singleShot
-        if not (self._agg_draw_pending or self._agg_is_drawing):
-            self._agg_draw_pending = True
-            QtCore.QTimer.singleShot(0, self.__draw_idle_agg)
-
-    def __draw_idle_agg(self, *args):
-        # if nothing to do, bail
-        if not self._agg_draw_pending:
-            return
-        # we have now tried this function at least once, do not run
-        # again until re-armed.  Doing this here rather than after
-        # protects against recursive calls triggered through self.draw
-        # The recursive call is via `repaintEvent`
-        self._agg_draw_pending = False
-        # if negative size, bail
-        if self.height() < 0 or self.width() < 0:
-            return
-        try:
-            # actually do the drawing
-            self.draw()
-        except Exception:
-            # Uncaught exceptions are fatal for PyQt5, so catch them instead.
-            traceback.print_exc()
-
     def blit(self, bbox=None):
         """Blit the region in bbox.
         """
@@ -182,23 +91,13 @@ def blit(self, bbox=None):
         self.repaint(l, self.renderer.height / self._dpi_ratio - t, w, h)
 
     def print_figure(self, *args, **kwargs):
-        super(FigureCanvasQTAggBase, self).print_figure(*args, **kwargs)
+        super(FigureCanvasQTAgg, self).print_figure(*args, **kwargs)
         self.draw()
 
 
-class FigureCanvasQTAgg(FigureCanvasQTAggBase, FigureCanvasQT):
-    """
-    The canvas the figure renders into.  Calls the draw and print fig
-    methods, creates the renderers, etc.
-
-    Modified to import from Qt5 backend for new-style mouse events.
-
-    Attributes
-    ----------
-    figure : `matplotlib.figure.Figure`
-        A high-level Figure instance
-
-    """
+@cbook.deprecated("2.2")
+class FigureCanvasQTAggBase(FigureCanvasQTAgg):
+    pass
 
 
 @_BackendQT5.export