A brave new world
Windows 8 will ship with a pair of runtimes; a new .NET runtime (currently version stamped 4.5), and a native code C++ runtime (technically, COM, or a derivative thereof), named WinRT. There will be a new native user interface library, DirectUI, that builds on top of the native Direct2D and DirectWrite APIs that were introduced with Windows 7. A new version of Silverlight, apparently codenamed Jupiter, will run on top of DirectUI. WinRT and DirectUI will both be directly accessible from .NET through built-in wrappers.
WinRT provides a clean and modern API for many of the things that Win32 does presently. It will be, in many ways, a new, modern Win32. The API is designed to be easy to use from "modern" C++ (in contrast to the 25 year old, heavily C-biased design of Win32); it will also map cleanly onto .NET concepts. In Windows 8, it's unlikely that WinRT will cover everything Win32 can do—Win32 is just so expansive that modernizing it is an enormous undertaking—but I'm told that this is the ultimate, long-term objective. And WinRT is becoming more and more extensive with each new build that leaks from Redmond.
WinRT isn't just providing a slightly nicer version of the existing Win32 API, either. Microsoft is taking the opportunity to improve the API's functionality, too. The clipboard API, for example, has been made easier to use and more flexible. There will also be pervasive support for asynchronous operations, providing a clean and consistent way to do long-running tasks in the background.
DirectUI is built around a core subset of current WPF/Silverlight technology. It includes support for XAML, the XML language for laying out user interfaces, and offers the rich support for layouts that Win32 has never had. This core will give C++ programs their modern user interface toolkit and, at its heart, it will be the same toolkit that .NET developers use too. (DirectUI is a name Microsoft has used before, internally, for a graphics library used by Windows Live Messenger. The new DirectUI appears to be unrelated.)
Jupiter is essentially Silverlight 6; a fully-featured, flexible toolkit for building applications. The exact relationship between DirectUI and Jupiter isn't entirely clear at the moment. It's possible that they're one and the same—and that DirectUI will grow in functionality until it's able to do everything that Silverlight can do. It's also possible that DirectUI will retain only core functionality, with a more complete framework built on top of its features. Another option is that Jupiter refers specifically to immersive, full-screen, touch-first applications.
Read more: Ars technica
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