This approach solves a common problem in apps that need to surface a lot of controls.
Problem 1: Sliders take up a lot of space.
Problem 2: Fine control of a mouse or touch-driven interface is provided by sliding, not by rotational gestures.
The idea here is to use a virtual knob to save space, while providing the fine control possible with a sliding interface. The sliding direction is generally chosen to be intuitive to the function of the knob. (Locking to horizontal or vertical also assists with fine control.)
Problem 1: Sliders take up a lot of space.
Problem 2: Fine control of a mouse or touch-driven interface is provided by sliding, not by rotational gestures.
The idea here is to use a virtual knob to save space, while providing the fine control possible with a sliding interface. The sliding direction is generally chosen to be intuitive to the function of the knob. (Locking to horizontal or vertical also assists with fine control.)