mono/MonoGame — pull request #1789 by borrillis (2013-06-14 11:21:25+00:00)
Title: Updated implementation of Texture2D.GetData<T> using subregion for MacOS and DirectX

Texture2D.GetData threw NotImplementedExceptions on both MacOS and DirectX if you supplied a Rectangle as the Source area. I have implemented that functionality for both platforms.