matplotlib · QuLogic · Jun 16, 2020 · Jun 15, 2020 · Jun 11, 2020 · Jun 15, 2020
diff --git a/lib/matplotlib/backend_bases.py b/lib/matplotlib/backend_bases.py
@@ -2293,7 +2293,7 @@ def start_event_loop(self, timeout=0):
         The event loop blocks until a callback function triggers
         `stop_event_loop`, or *timeout* is reached.
 
-        If *timeout* is negative, never timeout.
+        If *timeout* is 0 or negative, never timeout.
 
         Only interactive backends need to reimplement this method and it relies
         on `flush_events` being properly implemented.

diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
@@ -15,10 +15,12 @@
 import matplotlib.backends.qt_editor.figureoptions as figureoptions
 from matplotlib.backends.qt_editor.formsubplottool import UiSubplotTool
 from matplotlib.backend_managers import ToolManager
-
+from . import qt_compat
 from .qt_compat import (
     QtCore, QtGui, QtWidgets, _isdeleted, _getSaveFileName,
-    is_pyqt5, __version__, QT_API)
+    is_pyqt5, __version__, QT_API, _setDevicePixelRatioF,
+    _devicePixelRatioF)
+
 
 backend_version = __version__
 
@@ -267,12 +269,7 @@ def _update_figure_dpi(self):
 
     @property
     def _dpi_ratio(self):
-        # Not available on Qt4 or some older Qt5.
-        try:
-            # self.devicePixelRatio() returns 0 in rare cases
-            return self.devicePixelRatio() or 1
-        except AttributeError:
-            return 1
+        return _devicePixelRatioF(self)
 
     def _update_dpi(self):
         # As described in __init__ above, we need to be careful in cases with
@@ -454,8 +451,9 @@ def start_event_loop(self, timeout=0):
         if hasattr(self, "_event_loop") and self._event_loop.isRunning():
             raise RuntimeError("Event loop already running")
         self._event_loop = event_loop = QtCore.QEventLoop()
-        if timeout:
-            timer = QtCore.QTimer.singleShot(timeout * 1000, event_loop.quit)
+        if timeout > 0:
+            timer = QtCore.QTimer.singleShot(int(timeout * 1000),
+                                             event_loop.quit)
         event_loop.exec_()
 
     def stop_event_loop(self, event=None):
@@ -683,8 +681,7 @@ def _icon(self, name, color=None):
         if is_pyqt5():
             name = name.replace('.png', '_large.png')
         pm = QtGui.QPixmap(os.path.join(self.basedir, name))
-        if hasattr(pm, 'setDevicePixelRatio'):
-            pm.setDevicePixelRatio(self.canvas._dpi_ratio)
+        _setDevicePixelRatioF(pm, _devicePixelRatioF(self))
         if color is not None:
             mask = pm.createMaskFromColor(QtGui.QColor('black'),
                                           QtCore.Qt.MaskOutColor)

diff --git a/lib/matplotlib/backends/backend_qt5agg.py b/lib/matplotlib/backends/backend_qt5agg.py
@@ -11,7 +11,7 @@
 from .backend_qt5 import (
     QtCore, QtGui, QtWidgets, _BackendQT5, FigureCanvasQT, FigureManagerQT,
     NavigationToolbar2QT, backend_version)
-from .qt_compat import QT_API
+from .qt_compat import QT_API, _setDevicePixelRatioF
 
 
 class FigureCanvasQTAgg(FigureCanvasAgg, FigureCanvasQT):
@@ -64,9 +64,7 @@ def paintEvent(self, event):
 
             qimage = QtGui.QImage(buf, buf.shape[1], buf.shape[0],
                                   QtGui.QImage.Format_ARGB32_Premultiplied)
-            if hasattr(qimage, 'setDevicePixelRatio'):
-                # Not available on Qt4 or some older Qt5.
-                qimage.setDevicePixelRatio(self._dpi_ratio)
+            _setDevicePixelRatioF(qimage, self._dpi_ratio)
             # set origin using original QT coordinates
             origin = QtCore.QPoint(rect.left(), rect.top())
             painter.drawImage(origin, qimage)
@@ -87,7 +85,7 @@ def blit(self, bbox=None):
             bbox = self.figure.bbox
 
         # repaint uses logical pixels, not physical pixels like the renderer.
-        l, b, w, h = [pt / self._dpi_ratio for pt in bbox.bounds]
+        l, b, w, h = [int(pt / self._dpi_ratio) for pt in bbox.bounds]
         t = b + h
         self.repaint(l, self.renderer.height / self._dpi_ratio - t, w, h)
 

diff --git a/lib/matplotlib/backends/backend_qt5cairo.py b/lib/matplotlib/backends/backend_qt5cairo.py
@@ -2,7 +2,7 @@
 
 from .backend_cairo import cairo, FigureCanvasCairo, RendererCairo
 from .backend_qt5 import QtCore, QtGui, _BackendQT5, FigureCanvasQT
-from .qt_compat import QT_API
+from .qt_compat import QT_API, _setDevicePixelRatioF
 
 
 class FigureCanvasQTCairo(FigureCanvasQT, FigureCanvasCairo):
@@ -19,8 +19,8 @@ def draw(self):
     def paintEvent(self, event):
         self._update_dpi()
         dpi_ratio = self._dpi_ratio
-        width = dpi_ratio * self.width()
-        height = dpi_ratio * self.height()
+        width = int(dpi_ratio * self.width())
+        height = int(dpi_ratio * self.height())
         if (width, height) != self._renderer.get_canvas_width_height():
             surface = cairo.ImageSurface(cairo.FORMAT_ARGB32, width, height)
             self._renderer.set_ctx_from_surface(surface)
@@ -33,9 +33,7 @@ def paintEvent(self, event):
         # QImage under PySide on Python 3.
         if QT_API == 'PySide':
             ctypes.c_long.from_address(id(buf)).value = 1
-        if hasattr(qimage, 'setDevicePixelRatio'):
-            # Not available on Qt4 or some older Qt5.
-            qimage.setDevicePixelRatio(dpi_ratio)
+        _setDevicePixelRatioF(qimage, dpi_ratio)
         painter = QtGui.QPainter(self)
         painter.eraseRect(event.rect())
         painter.drawImage(0, 0, qimage)

diff --git a/lib/matplotlib/backends/qt_compat.py b/lib/matplotlib/backends/qt_compat.py
@@ -173,4 +173,38 @@ def is_pyqt5():
 # These globals are only defined for backcompatibility purposes.
 ETS = dict(pyqt=(QT_API_PYQTv2, 4), pyside=(QT_API_PYSIDE, 4),
            pyqt5=(QT_API_PYQT5, 5), pyside2=(QT_API_PYSIDE2, 5))
-QT_RC_MAJOR_VERSION = 5 if is_pyqt5() else 4
+
+QT_RC_MAJOR_VERSION = int(QtCore.qVersion().split(".")[0])
+
+
+def _devicePixelRatioF(obj):
+    """
+    Return obj.devicePixelRatioF() with graceful fallback for older Qt.
+
+    This can be replaced by the direct call when we require Qt>=5.6.
+    """
+    try:
+        # Not available on Qt<5.6
+        return obj.devicePixelRatioF() or 1
+    except AttributeError:
+        pass
+    try:
+        # Not available on Qt4 or some older Qt5.
+        # self.devicePixelRatio() returns 0 in rare cases
+        return obj.devicePixelRatio() or 1
+    except AttributeError:
+        return 1
+
+
+def _setDevicePixelRatioF(obj, val):
+    """
+    Call obj.setDevicePixelRatioF(val) with graceful fallback for older Qt.
+
+    This can be replaced by the direct call when we require Qt>=5.6.
+    """
+    if hasattr(obj, 'setDevicePixelRatioF'):
+        # Not available on Qt<5.6
+        obj.setDevicePixelRatioF(val)
+    elif hasattr(obj, 'setDevicePixelRatio'):
+        # Not available on Qt4 or some older Qt5.
+        obj.setDevicePixelRatio(val)
diff --git a/lib/matplotlib/tests/test_backend_qt.py b/lib/matplotlib/tests/test_backend_qt.py
@@ -253,6 +253,29 @@ def test_dpi_ratio_change():
         assert qt_canvas.get_width_height() == (600, 240)
         assert (fig.get_size_inches() == (5, 2)).all()
 
+        p.return_value = 1.5
+
+        assert qt_canvas._dpi_ratio == 1.5
+
+        qt_canvas.draw()
+        qApp.processEvents()
+        # this second processEvents is required to fully run the draw.
+        # On `update` we notice the DPI has changed and trigger a
+        # resize event to refresh, the second processEvents is
+        # required to process that and fully update the window sizes.
+        qApp.processEvents()
+
+        # The DPI and the renderer width/height change
+        assert fig.dpi == 180
+        assert qt_canvas.renderer.width == 900
+        assert qt_canvas.renderer.height == 360
+
+        # The actual widget size and figure physical size don't change
+        assert size.width() == 600
+        assert size.height() == 240
+        assert qt_canvas.get_width_height() == (600, 240)
+        assert (fig.get_size_inches() == (5, 2)).all()
+
 
 @pytest.mark.backend('Qt5Agg')
 def test_subplottool():