Wednesday, February 29, 2012

Architecture of WPF

Architecture in the Presentation Layer
  • "The software architecture of a program or computing system is the structure or structures of the system, which comprise software elements, the externally visible properties of those elements, and the relationships among them."
    - From the book Software Architecture in Practice (2nd edition), (Bass, Clements, Kazman;Addison-Wesley 2003)
  • WPF has a rich and extensible architecture for designing compelling UI applications
WPF uses a multi layered architecture. At the top, application interacts with a high-level set of services that are completely written in managed C# code. The actual work of translating .NET objects into Direct3D textures and triangles happens behind the scenes, using a lower level unmanaged component called milcore.dll.
milcore.dll is implemented in unmanaged code because it needs tight integration with Direct3D and because it’s extremely performance-sensitive.
Figure : WPF rendering architecture
Key components:
  • PresentationFramework.dll holds the top-level WPF types, including those that represent windows, panels, and other types of controls. It also implements higher-level programming abstractions such as styles. Most of the classes you’ll use directly come from this assembly.
  • PresentationCore.dll holds base types, such as UIElement and Visual, from which all shapes and controls derive. If you don’t need the full window and control abstraction layer, you can drop down to this level and still take advantage of WPF’s rendering engine.
  • WindowsBase.dll holds even more basic ingredients that have the potential to be reused outside of WPF, such as DispatcherObject and DependencyObject, which introduces the plumbing for dependency properties.
  • milcore.dll is the core of the WPF rendering system and the foundation of the Media Integration Layer (MIL). Its composition engine translates visual elements into the triangle and textures that Direct3D expects. Although milcore.dll is considered a part of WPF, it’s also an essential system component for Windows Vista. In fact, the Desktop Window Manager (DWM) in Windows Vista uses milcore.dll to render the desktop.
  • milcore.dll is sometimes referred to as the engine for “managed graphics.” Much as the common language runtime (CLR) manages the lifetime of a .NET application, milcore.dll manages the display state. And just as the CLR saves you from worrying about releasing objects and reclaiming memory, milcore.dll saves you from thinking about invalidating and repainting a window.
  • WindowsCodecs.dll is a low-level API that provides imaging support (for example, processing, displaying, and scaling bitmaps and JPEGs).
  • Direct3D is the low-level API through which all the graphics in a WPF are rendered.
  • User32 is used to determine what program gets what real estate. As a result, it’s still involved in WPF, but it plays no part in rendering common controls.
The Class Hierarchy
Figure shows a basic overview with some of the key branches of the class hierarchy:
Figure : The fundamental classes of WPF

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