HGGLDial Open Source

This dial widget is an advanced rotation control that you can easily include into any Android project in the form of an AAR file (Androids’ equivalent of a JAR file). You can think of this Dial control as a gesture library that is just concerned with rotation; having all of the conceivable behaviour you could possibly want in a rotation control.
Features of the HGGLDial Library:

1 Powered by OpenGLES 2.0 this is a very powerful and responsive library.
2 Simple classic Android usage, modeled on classic Android programming patterns.
3 A dynamic return type, returned in a callback containing all the status information you will need for any programming scenarios.
4 Open ended architecture to achieve maximum usage scenarios.
5 Dial objects have the ability to act upon other dial objects, ie interacting with one dial can cause rotation in another dial at various rates of rotation (see Clock Demo in the demo app).
6 Feature to distort a dial and rotate along the distortion (see Distortion Demo in the demo app).
7 Advanced rotate snapping behavior with advanced proximity settings (ability to rotate freely for a certain amount of degrees before snap event occurs).
8 Sensitivity settings. You can make the dial rotate slower or faster than the gesture or even in the opposite direction of the gesture.
9 Single finger or dual finger mode.
10 Cumulative and non cumulative rotation behavior. The dial can rotate directly to where the gesture starts or only rotate when the gesture moves; moving relative to the touch motion.
11 The control keeps track of: The number of circular gestures, the number of image rotations, the direction of rotation, the XY positions of the touches from the gesture and the angle at which the touch is occurring.
12 Minimum/Maximum rotation constraints. You can set the dial control to stop rotating at a certain number of rotations (clockwise or counter-clockwise).
13 Alpha blending (see Clock Demo in the demo app).
14 It is possible to adjust the center point of rotation for any image.
15 It is possible to change the touch XY origin allowing you to rotate from a different position.
16 It has a variable dial behavior causing the rotation rate to change depending on how close the gesture is the center of the dial.
17 Last but not least: It’s open source and FREE to use.

This library supports API 9+
There is a Canvas/Extended View version of this library. If you don't need the distorted dial feature or do not need to have one dial act upon another then it is best to use the library 'HGDial' which can be found in the same repository.