Though WPF is mainly used for desktop applications, you can also create web-based applications. Thus, WPF applications can be of two types:
- Desktop-based executables (EXE)
- Web-based applications (XBAP)
The desktop applications are the normal .exe executables, which you normally run on any of your Windows-based systems, whereas the web-based applications are the .xbap files that can be deployed in web servers and can run inside any supported browser. The .NET Framework is mandatory to run any of these application types.
When you run a WPF application, it starts in two threads. The UI thread uses the System.Threading.DispatcherObject to create the messaging system and that maintains the UI operations queue. Just like the Win32 message pumping, it performs the UI operation based on the priority set for it.
The other thread is the background thread, which is used to handle the rendering engine being managed by WPF. It picks up a copy of the visual tree and performs actions to show the visual components in the Direct3D surface. Then it calls the UI elements to determine the size and arranges the child elements by their parents.