Added clarity on bounding box construction.

pshriwise · pshriwise · commit 13237c2f116d · 2019-08-27T12:49:47.000-05:00
diff --git a/lib/matplotlib/backends/backend_qt5agg.py b/lib/matplotlib/backends/backend_qt5agg.py
@@ -48,9 +48,11 @@ def paintEvent(self, event):
         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
+        bottom = top - height
+        # same with the right side of the image
+        right = left + width
+        # create a buffer using the image bounding box
+        bbox = Bbox([[left, bottom], [right, top]])
         reg = self.copy_from_bbox(bbox)
         buf = cbook._unmultiplied_rgba8888_to_premultiplied_argb32(
             memoryview(reg))
