The last three buttons of the Camera View toolbar (A, B, and C,) are the Display options and let you configure elements of the Viewer window display.
Display Options A.Trajectories B. 2D Magnifier C. Selective Redraw
To view the trajectory for any animated object, select the object, and click the Trajectories button. Expand the Trajectories menu to view the Trajectories menu options.
When the Selective Redraw option is activated it refreshes the current scene in the Viewer window without updating the operations in any other window.
