Make the Qt interactive zoom rectangle black & white.

anntzer · anntzer · commit e0b65253a61a · 2020-05-01T18:59:41.000+02:00
Explicitly drawing white segments makes it visible even over dark
backgrounds.
diff --git a/doc/users/next_whats_new/2020-03-16-qtzoom.rst b/doc/users/next_whats_new/2020-03-16-qtzoom.rst
@@ -0,0 +1,4 @@
+Qt zoom rectangle now black and white
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This makes it visible even over a dark background.
diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
@@ -479,10 +479,15 @@ def drawRectangle(self, rect):
         # 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)
+                scaled_rect = [pt / self._dpi_ratio for pt in rect]
+                pen = QtGui.QPen(QtCore.Qt.black, 1 / self._dpi_ratio)
+                pen.setDashPattern([3, 3])
                 painter.setPen(pen)
-                painter.drawRect(*(pt / self._dpi_ratio for pt in rect))
+                painter.drawRect(*scaled_rect)
+                pen.setDashOffset(3)
+                pen.setColor(QtCore.Qt.white)
+                painter.setPen(pen)
+                painter.drawRect(*scaled_rect)
         else:
             def _draw_rect_callback(painter):
                 return
