The 'QmitkSliceNavigationListener' and its 'SliceChanged' signal work, but the currently selected position does not return the correct position. This is due to the fact, that the 'QmitkStdMultiWidgetEditor' returns the cross-position of the StdMultiWidget when calling 'GetSelectedPosition(nullptr)'. The cross-position itself is in turn computed by the intersection of the different plane geometries. Since the planes do not have a point of intersection anymore, this approach does not work either.

The current way to go is now to catch the mouse click event of a render window and process it to return the correct position. This works but navigating using the ImageNavigatorPlugin does not show the crosshair correctly.

There seems to be a problem with this approach, too: When setting all three 2D render windows to the same plane, the mouse click event is still caught and the position changes according to the click-position. But the point from the point set does not change its position accordingly. The approach works if one of the 2D render windows is set to a different view plane.

EDIT: There was a render window update call missing. The update call needs to be done explicitly in this case. If all render windows show an image from the same view direction (same anatomical plane) and the position of the crosshair is changed via mouse click, the image itself is not redrawn, since the crosshair is only moved along the plane (mouse click in 2D). No slice is changed. Therefore no render window update was performed in this case.

Pushed new branch T22876-Render-window-manager-crosshair.

An update is needed, since an already existing crosshair from a previously opened render window manager won't be overwritten / reused. This leads to multiple Render Window Manager Crosshairs in the DataManager if the plugin is closed and reopened several times.