Merge pull request matplotlib#18737 from alexschlueter/fix_transformed_img_cursor

Fix data cursor for images with additional transform

Author: jklymak

lib/matplotlib/image.py

@@ -660,7 +660,8 @@ def contains(self, mouseevent):
         # collection on nonlinear transformed coordinates.
         # TODO: consider returning image coordinates (shouldn't
         # be too difficult given that the image is rectilinear
-        x, y = mouseevent.xdata, mouseevent.ydata
+        trans = self.get_transform().inverted()
+        x, y = trans.transform([mouseevent.x, mouseevent.y])
         xmin, xmax, ymin, ymax = self.get_extent()
         if xmin > xmax:
             xmin, xmax = xmax, xmin
@@ -982,13 +983,14 @@ def get_cursor_data(self, event):
         if self.origin == 'upper':
             ymin, ymax = ymax, ymin
         arr = self.get_array()
-        data_extent = Bbox([[ymin, xmin], [ymax, xmax]])
-        array_extent = Bbox([[0, 0], arr.shape[:2]])
-        trans = BboxTransform(boxin=data_extent, boxout=array_extent)
-        point = trans.transform([event.ydata, event.xdata])
+        data_extent = Bbox([[xmin, ymin], [xmax, ymax]])
+        array_extent = Bbox([[0, 0], [arr.shape[1], arr.shape[0]]])
+        trans = self.get_transform().inverted()
+        trans += BboxTransform(boxin=data_extent, boxout=array_extent)
+        point = trans.transform([event.x, event.y])
         if any(np.isnan(point)):
             return None
-        i, j = point.astype(int)
+        j, i = point.astype(int)
         # Clip the coordinates at array bounds
         if not (0 <= i < arr.shape[0]) or not (0 <= j < arr.shape[1]):
             return None

lib/matplotlib/tests/test_image.py

@@ -325,6 +325,15 @@ def test_cursor_data():
     event = MouseEvent('motion_notify_event', fig.canvas, xdisp, ydisp)
     assert im.get_cursor_data(event) is None
 
+    # Now try with additional transform applied to the image artist
+    trans = Affine2D().scale(2).rotate(0.5)
+    im = ax.imshow(np.arange(100).reshape(10, 10),
+                   transform=trans + ax.transData)
+    x, y = 3, 10
+    xdisp, ydisp = ax.transData.transform([x, y])
+    event = MouseEvent('motion_notify_event', fig.canvas, xdisp, ydisp)
+    assert im.get_cursor_data(event) == 44
+
 
 @pytest.mark.parametrize(
     "data, text_without_colorbar, text_with_colorbar", [