Removes the current bitmap-based graphics context from the top of the stack.
- iOS 2.0+
- tvOS 9.0+
- watchOS 2.0+
You use this function to clean up the drawing environment put in place by the
UIGraphics function and to remove the corresponding bitmap-based graphics context from the top of the stack. If the current context was not created using the
UIGraphics function, this function does nothing.
This function may be called from any thread of your app.