Returns an image based on the contents of the current bitmap-based graphics context.
- iOS 2.0+
- tvOS 9.0+
- watchOS 2.0+
A image object containing the contents of the current bitmap graphics context.
You should call this function only when a bitmap-based graphics context is the current graphics context. If the current context is
nil or was not created by a call to
UIGraphics, this function returns
This function may be called from any thread of your app.