The file sound.c++ contains a subtree that positions volume controls at the top of the viewing screen for the application. The node layout is shown in Figure 5. The "Up" and "Down" displayed text are selectable and their respective callback functions change the volume of the audio out port. Each consists of a SoSelection node, a transform and the SoText2 itself. Between the two selectable texts is the "Volume" label. This text is not selectable.