Function selection_frame 

pub fn selection_frame(
    world: &GameWorld,
    editor_state: &EditorState,
    view_info: &ViewInfo,
) -> Option<SelectionFrame>

The frame the manipulator occupies for the current selection, or None when nothing is selected.

The pivot is the mean of the selected origins, so a multi-selection rotates and scales as one body rather than each entity about itself.