Using different corner to avoid off-by-one issue.

pshriwise · pshriwise · commit 7db54c0ab554 · 2019-06-04T23:11:27.000-05:00
diff --git a/lib/matplotlib/backends/backend_qt5agg.py b/lib/matplotlib/backends/backend_qt5agg.py
@@ -38,13 +38,15 @@ def paintEvent(self, event):
 
         painter = QtGui.QPainter(self)
 
-        # get bounding box scaled to the figure
+        # See documentation of QRect: bottom() and right() are off by 1, so use
+        # left() + width() and top() + height().
         rect = event.rect()
-        left, top = self.mouseEventCoords(rect.bottomLeft())
         width = rect.width() * self._dpi_ratio
         height = rect.height() * self._dpi_ratio
-        # See documentation of QRect: bottom() and right() are off by 1, so use
-        # left() + width() and top() + height().
+        left, top = self.mouseEventCoords(rect.topLeft())
+        # shift the "top" by the height of the image to get the
+        # correct corner for our coordinate system
+        top -= height
         bbox = Bbox([[left, top], [left + width, top + height]])
         # create a buffer using this bounding box
         reg = self.copy_from_bbox(bbox)
@@ -59,6 +61,7 @@ def paintEvent(self, event):
         if hasattr(qimage, 'setDevicePixelRatio'):
             # Not available on Qt4 or some older Qt5.
             qimage.setDevicePixelRatio(self._dpi_ratio)
+        # set origin using original QT coordinates
         origin = QtCore.QPoint(rect.left(), rect.top())
         painter.drawImage(origin, qimage)
         # Adjust the buf reference count to work around a memory
