When calculating view directions, check ndim, not just ndisplay (napa…

…ri#7301)

# References and relevant issues

Closes: napari#7299

# Description

Rather than just checking ndisplay, which can be 3 for a 2D layer (ndim
being 2), this PR adds a check that `ndim` isn't 2.

I also added a test that fails without this PR, but passes with it.

napari/_qt/_tests/test_qt_viewer.py

@@ -517,6 +517,35 @@ def on_click(layer, event):
     view.canvas._process_mouse_event(mouse_press_callbacks, mouse_event)
 
 
+def test_process_mouse_event_2d_layer_3d_viewer(make_napari_viewer):
+    """Test that _process_mouse_events can handle 2d layers in 3D.
+
+    This is a test for: https://github.com/napari/napari/issues/7299
+    """
+
+    # make a mock mouse event
+    new_pos = [5, 5]
+    mouse_event = MouseEvent(
+        pos=new_pos,
+    )
+    data = np.zeros((20, 20))
+
+    viewer = make_napari_viewer()
+    view = viewer.window._qt_viewer
+    image = viewer.add_image(data)
+
+    @image.mouse_drag_callbacks.append
+    def on_click(layer, event):
+        expected_position = view.canvas._map_canvas2world(new_pos)
+        np.testing.assert_almost_equal(expected_position, list(event.position))
+
+    assert viewer.dims.ndisplay == 2
+    view.canvas._process_mouse_event(mouse_press_callbacks, mouse_event)
+
+    viewer.dims.ndisplay = 3
+    view.canvas._process_mouse_event(mouse_press_callbacks, mouse_event)
+
+
 @skip_local_popups
 def test_memory_leaking(qtbot, make_napari_viewer):
     data = np.zeros((5, 20, 20, 20), dtype=int)

napari/_vispy/canvas.py

@@ -640,7 +640,7 @@ def _add_overlay_to_visual(self, overlay: Overlay) -> None:
     def _calculate_view_direction(self, event_pos: list[float]) -> list[float]:
         """calculate view direction by ray shot from the camera"""
         # this method is only implemented for 3 dimension
-        if self.viewer.dims.ndisplay == 2:
+        if self.viewer.dims.ndisplay == 2 or self.viewer.dims.ndim == 2:
             return self.viewer.camera.calculate_nd_view_direction(
                 self.viewer.dims.ndim, self.viewer.dims.displayed
             )