Windows Presentation Foundation

Windows Presentation Foundation (WPF; codenamed Avalon) is a user interface subsystem that relies on .NET Framework and .NET Core. It was designed for more complex UI designs than the standard Windows Forms subsystem could offer. It also has support for DirectX and Direct3D graphical models.

The WPF runtime libraries are included in Windows starting from Windows Vista. WPF applications can be created using Visual Studio IDE and Microsoft Blend (formerly Microsoft Expression Blend). The system uses an XML-based language called XAML to define user elements and is extended onto the web by using Microsoft Silverlight.

Development
Just like WinFS, Avalon was first introduced in PDC 2003. At PDC, Microsoft explained how Avalon is a vector graphics-based app interface engine, how easy it is to program it with WinFX (later known as .NET Framework 3.0) and what it enables for applications (such as transparency and app animations).

Later, in PDC 2005, Microsoft announced 2 new tools to be used for developing Avalon apps:


 * Sparkle: Later known as Microsoft Blend/Microsoft Expression Blend
 * Cider: A tool to design WPF and Silverlight apps, later merged with Visual Studio.

December 2005 saw the release of WinFX Extensions for Visual Studio 2005 (Community Technology Preview) and WPF reached RTM on 21 November 2006 as part of .NET Framework 3.0. On the other hand, Sparkle was later renamed to Microsoft Expression Blend on December 2006. On January 2007, the first CTP of Expression Blend was released. Finally, the RTM of Expression Blend arrived on 30 April 2007.

Microsoft announced Windows Presentation Foundation would be open-source and will be released under the MIT license at the Microsoft Connect 2018 keynote. This also enabled WPF to use the open-source .NET Core framework.