Unify QtAgg nonblitting and blitting code paths.

Follow a similar architecture to the Gtk3Agg backend: a default draw can be implemented as a blitting of the entire canvas. Also unify the Qt4Agg and Qt5Agg canvas classes a bit more.
matplotlib · tacaswell · Jul 9, 2017 · Jun 18, 2017 · Jun 15, 2017 · Jun 14, 2017
commit 65a0ccc3294efd0bebd1485fb67d3c78920c0aaa
diff --git a/lib/matplotlib/backends/backend_qt4agg.py b/lib/matplotlib/backends/backend_qt4agg.py
@@ -15,7 +15,7 @@
 from matplotlib.figure import Figure
 
 
-from .backend_qt5agg import FigureCanvasQTAggBase as _FigureCanvasQTAggBase
+from .backend_qt5agg import FigureCanvasQTAggBase
 
 from .backend_agg import FigureCanvasAgg
 from .backend_qt4 import QtCore
@@ -54,13 +54,7 @@ def new_figure_manager_given_figure(num, figure):
     return FigureManagerQT(canvas, num)
 
 
-class FigureCanvasQTAggBase(_FigureCanvasQTAggBase):
-    def __init__(self, figure):
-        self._agg_draw_pending = False
-
-
-class FigureCanvasQTAgg(FigureCanvasQTAggBase,
-                        FigureCanvasQT, FigureCanvasAgg):
+class FigureCanvasQTAgg(FigureCanvasQTAggBase, FigureCanvasQT):
     """
     The canvas the figure renders into.  Calls the draw and print fig
     methods, creates the renderers, etc...
@@ -72,16 +66,6 @@ class FigureCanvasQTAgg(FigureCanvasQTAggBase,
 
     """
 
-    def __init__(self, figure):
-        if DEBUG:
-            print('FigureCanvasQtAgg: ', figure)
-        FigureCanvasQT.__init__(self, figure)
-        FigureCanvasQTAggBase.__init__(self, figure)
-        FigureCanvasAgg.__init__(self, figure)
-        self._drawRect = None
-        self.blitbox = []
-        self.setAttribute(QtCore.Qt.WA_OpaquePaintEvent)
-
 
 FigureCanvas = FigureCanvasQTAgg
 FigureManager = FigureManagerQT
diff --git a/lib/matplotlib/backends/backend_qt5agg.py b/lib/matplotlib/backends/backend_qt5agg.py
@@ -7,10 +7,11 @@
 import six
 
 import ctypes
-import sys
 import traceback
 
+from matplotlib import cbook
 from matplotlib.figure import Figure
+from matplotlib.transforms import Bbox
 
 from .backend_agg import FigureCanvasAgg
 from .backend_qt5 import QtCore
@@ -28,11 +29,6 @@
 
 DEBUG = False
 
-_decref = ctypes.pythonapi.Py_DecRef
-_decref.argtypes = [ctypes.py_object]
-_decref.restype = None
-
-
 def new_figure_manager(num, *args, **kwargs):
     """
     Create a new figure manager instance
@@ -52,7 +48,7 @@ def new_figure_manager_given_figure(num, figure):
     return FigureManagerQT(canvas, num)
 
 
-class FigureCanvasQTAggBase(object):
+class FigureCanvasQTAggBase(FigureCanvasAgg):
     """
     The canvas the figure renders into.  Calls the draw and print fig
     methods, creates the renderers, etc...
@@ -66,7 +62,10 @@ class FigureCanvasQTAggBase(object):
 
     def __init__(self, figure):
         super(FigureCanvasQTAggBase, self).__init__(figure=figure)
+        self.setAttribute(QtCore.Qt.WA_OpaquePaintEvent)
         self._agg_draw_pending = False
+        self._bbox_queue = []
+        self._drawRect = None
 
     def drawRectangle(self, rect):
         if rect is not None:
@@ -75,6 +74,11 @@ def drawRectangle(self, rect):
             self._drawRect = None
         self.update()
 
+    @property
+    @cbook.deprecated("2.1")
+    def blitbox(self):
+        return self._bbox_queue
+
     def paintEvent(self, e):
         """
         Copy the image from the Agg canvas to the qt.drawable.
@@ -86,88 +90,41 @@ def paintEvent(self, e):
         if not hasattr(self, 'renderer'):
             return
 
-        if DEBUG:
-            print('FigureCanvasQtAgg.paintEvent: ', self,
-                  self.get_width_height())
-
-        if len(self.blitbox) == 0:
-            # matplotlib is in rgba byte order.  QImage wants to put the bytes
-            # into argb format and is in a 4 byte unsigned int.  Little endian
-            # system is LSB first and expects the bytes in reverse order
-            # (bgra).
-            if QtCore.QSysInfo.ByteOrder == QtCore.QSysInfo.LittleEndian:
-                stringBuffer = self.renderer._renderer.tostring_bgra()
-            else:
-                stringBuffer = self.renderer._renderer.tostring_argb()
-
-            refcnt = sys.getrefcount(stringBuffer)
-
-            # convert the Agg rendered image -> qImage
-            qImage = QtGui.QImage(stringBuffer, self.renderer.width,
-                                  self.renderer.height,
-                                  QtGui.QImage.Format_ARGB32)
-            if hasattr(qImage, 'setDevicePixelRatio'):
-                # Not available on Qt4 or some older Qt5.
-                qImage.setDevicePixelRatio(self._dpi_ratio)
-            # get the rectangle for the image
-            rect = qImage.rect()
-            p = QtGui.QPainter(self)
-            # reset the image area of the canvas to be the back-ground color
-            p.eraseRect(rect)
-            # draw the rendered image on to the canvas
-            p.drawPixmap(QtCore.QPoint(0, 0), QtGui.QPixmap.fromImage(qImage))
-
-            # 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)
-                p.setPen(pen)
-                x, y, w, h = self._drawRect
-                p.drawRect(x, y, w, h)
-            p.end()
-
-            # This works around a bug in PySide 1.1.2 on Python 3.x,
-            # where the reference count of stringBuffer is incremented
-            # but never decremented by QImage.
-            # TODO: revert PR #1323 once the issue is fixed in PySide.
-            del qImage
-            if refcnt != sys.getrefcount(stringBuffer):
-                _decref(stringBuffer)
+        painter = QtGui.QPainter(self)
+
+        if self._bbox_queue:
+            bbox_queue = self._bbox_queue
         else:
-            p = QtGui.QPainter(self)
-
-            while len(self.blitbox):
-                bbox = self.blitbox.pop()
-                l, b, r, t = bbox.extents
-                w = int(r) - int(l)
-                h = int(t) - int(b)
-                t = int(b) + h
-                reg = self.copy_from_bbox(bbox)
-                stringBuffer = reg.to_string_argb()
-                qImage = QtGui.QImage(stringBuffer, w, h,
-                                      QtGui.QImage.Format_ARGB32)
-                if hasattr(qImage, 'setDevicePixelRatio'):
-                    # Not available on Qt4 or some older Qt5.
-                    qImage.setDevicePixelRatio(self._dpi_ratio)
-                # Adjust the stringBuffer reference count to work
-                # around a memory leak bug in QImage() under PySide on
-                # Python 3.x
-                if QT_API == 'PySide' and six.PY3:
-                    ctypes.c_long.from_address(id(stringBuffer)).value = 1
-
-                origin = QtCore.QPoint(l, self.renderer.height - t)
-                pixmap = QtGui.QPixmap.fromImage(qImage)
-                p.drawPixmap(origin / self._dpi_ratio, pixmap)
-
-            # 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)
-                p.setPen(pen)
-                x, y, w, h = self._drawRect
-                p.drawRect(x, y, w, h)
-
-            p.end()
+            painter.eraseRect(self.rect())
+            bbox_queue = [
+                Bbox([[0, 0], [self.renderer.width, self.renderer.height]])]
+        self._bbox_queue = []
+        for bbox in bbox_queue:
+            l, b, r, t = map(int, bbox.extents)
+            w = r - l
+            h = t - b
+            reg = self.copy_from_bbox(bbox)
+            buf = reg.to_string_argb()
+            qimage = QtGui.QImage(buf, w, h, QtGui.QImage.Format_ARGB32)
+            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)
+
+        painter.end()
 
     def draw(self):
         """
@@ -213,7 +170,7 @@ def blit(self, bbox=None):
         if bbox is None and self.figure:
             bbox = self.figure.bbox
 
-        self.blitbox.append(bbox)
+        self._bbox_queue.append(bbox)
 
         # repaint uses logical pixels, not physical pixels like the renderer.
         l, b, w, h = [pt / self._dpi_ratio for pt in bbox.bounds]
@@ -225,8 +182,7 @@ def print_figure(self, *args, **kwargs):
         self.draw()
 
 
-class FigureCanvasQTAgg(FigureCanvasQTAggBase,
-                        FigureCanvasQT, FigureCanvasAgg):
+class FigureCanvasQTAgg(FigureCanvasQTAggBase, FigureCanvasQT):
     """
     The canvas the figure renders into.  Calls the draw and print fig
     methods, creates the renderers, etc.
@@ -244,14 +200,11 @@ def __init__(self, figure):
         if DEBUG:
             print('FigureCanvasQtAgg: ', figure)
         super(FigureCanvasQTAgg, self).__init__(figure=figure)
-        self._drawRect = None
-        self.blitbox = []
         # We don't want to scale up the figure DPI more than once.
         # Note, we don't handle a signal for changing DPI yet.
         if not hasattr(self.figure, '_original_dpi'):
             self.figure._original_dpi = self.figure.dpi
         self.figure.dpi = self._dpi_ratio * self.figure._original_dpi
-        self.setAttribute(QtCore.Qt.WA_OpaquePaintEvent)
 
 
 FigureCanvas = FigureCanvasQTAgg