kEAGLDrawablePropertyRetainedBacking

The key specifying whether the drawable surface retains its contents after displaying them. The value for this key is an NSNumber object containing a BOOL data type. If false, you may not rely on the contents being the same after the contents are displayed. If true, then the contents will not change after being displayed. Setting the value to true is recommended only when you need the content to remain unchanged, as using it can result in both reduced performance and additional memory usage. The default value is false.

let kEAGLDrawablePropertyRetainedBacking: String