WPF Introduction

The Windows Presentation Foundation (or WPF) is a graphical subsystem for rendering user interfaces in Windows-based applications. WPF, was initially released as part of .NET Framework 3.0. Designed to remove dependencies on the aging GDI subsystem, WPF is built on DirectX, which provides hardware acceleration and enables modern UI features like transparency, gradients and transforms. WPF provides a consistent programming model for building applications and provides a clear separation between the user interface and the business logic.

WPF also offers a new markup language, known as XAML which is an alternative means for defining UI elements and relationships with other UI elements. A WPF application can be deployed on the desktop or hosted in a web browser. It also enables rich control, design, and development of the visual aspects of Windows programs. It aims to unify a number of application services: user interface, 2D and 3D drawing, fixed and adaptive documents, advanced typography, vector graphics, raster graphics, animation, data binding, audio and video.

Microsoft Silverlight is a web-based subset of WPF that enables Flash-like web and mobile applications with the same programming model as .NET applications. 3D features are not supported, but XPS and vector-based drawing are included.

It is compatible with multiple web browser products used on Microsoft Windows, Linux (using Novell Moonlight), Mac OS X operating systems & Mobile devices.

WPF is designed to allow you to create dynamic, data driven presentation systems. Every part of the system is designed to create objects through property sets that drive behavior. Data binding is a fundamental part of the system, and is integrated at every layer.

Traditional applications create a display and then bind to some data. In WPF, everything about the control, every aspect of the display, is generated by some type of data binding. The text found inside a button is displayed by creating a composed control inside of the button and binding its display to the button’s content property.

Display technology evolution on windows …

  • User32 : Standard controls like buttons, textbox etc. This provides the windows look and feel for buttons and textboxes and other UI elements. User32 lacked drawing capabilities. Window forms are using User32 to render several controls including .net 2.0,vb, vc++ etc.
  • GDI (Graphics device interface) : Abstract graphics of drawing from hardware’s like printers ,monitors etc. Microsoft introduced GDI to provide drawing capabilities. GDI not only provided drawing capabilities but also provided a high level of abstraction on the hardware display. In other words it encapsulates all complexities of hardware in the GDI API. Several GDI API are available in windows platform to perform custom drawing. Hooks like subclassing cab be used to override default drawing of win32 controls on windows Or developers can create custom controls and use GDI API’s to render on screen.
  • GDI+ : JPG, PNG Image support, gradient shading, Anti Alising. GDI+ was introduced which basically extends GDI and provides extra functionalities like jpg and PNG support, gradient shading and anti-aliasing. The biggest issue with GDI API was it did not use hardware acceleration and did not have animation and 3D support. Object oriented approach to flat GDI+ API’s are available in .net which internally based on GDI+.
  • DirectX : Targeted for game programmers, Hardware  Acceleration (is a process in which we use hardware to perform some functions rather than performing those functions using the software which is running in the CPU.),support for animation,3D support, full colour graphics, Capture and play streaming media. One of the biggest issues with GDI and its extension GDI+ was hardware acceleration and animation support. This came as a biggest disadvantage for game developers. To answer and server game developers Microsoft developed DirectX. DirectX exploited hardware acceleration, had support for 3D, full color graphics , media streaming facility and lot more.
  • WPF : Based on direct (internally), support for primitive objects like text, shapes, controls etc, declarative UI using XAML, support for audio , video formats, define styles and templates for UI elements.  DirectX had this excellent feature of using hardware acceleration. Microsoft wanted to develop UI elements like textboxes,button,grids etc using the DirectX technology by which they can exploit the hardware acceleration feature. As WPF stands on the top of directX you can not only build simple UI elements but also go one step further and develop special UI elements like Grid, FlowDocument, and Ellipse. Oh yes you can go one more step further and build animations.WPF is not meant for game development. DirectX still will lead in that scenario. In case you are looking for light animation ( not game programming ) WPF will be a choice. You can also express WPF using XML which is also called as XAML.In other words WPF is a wrapper which is built over DirectX.

 The figure shows the overall architecture of WPF. It has three major sections presentation core, presentation framework and milcore.

 User32 :  It decides which goes where on the screen. 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.

  • DirectX : WPF uses directX internally. DirectX talks with drivers and renders the content.
  • Milcore :  Mil stands for media integration library. This section is a unmanaged code because it acts like a bridge between WPF managed and DirectX / User32 unmanaged API. The composition engine in milcore is extremely performance sensitive, and required giving up many advantages of the CLR to gain performance. 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. Though milcore.dll is considered a part of WPF, it’s also an essential system component for Windows Vista. The Desktop Window Manager (DWM) in Windows Vista uses milcore.dll to render the desktop.
  • Presentation core :– This is a low level API exposed by WPF providing features for 2D , 3D , geometry etc.,  includes base types, such as UIElement and Visual, from which all shapes and controls derive.
  • Presentation framework :  This section has high level features like application controls , layouts . Content etc which helps you to build up your application. The vast majority of Windows Presentation Foundation developers will work exclusively with this layer.
  • *Red colour box indicate WPF layer.


Silverlight : WPF on web – platform independence

The Silverlight runtime plug-in is essentially a ‘micro’ version of the .NET CLR. This runtime is hosted�
within the client side browser. This runtime will host your Silverlight assemblies, as well as the Silverlight base class libraries. This runtime will JIT CIL code, handle threads, exceptions and garbage collection. This is a good thing, as your current .NET programming skills apply directly to Silverlight development.

In addition to the ‘micro-CLR’, Silverlight supports a subset of the .NET base class libraries. When a�
requesting browser loads a Silverlight page, any required assemblies are downloaded to the user’s machine, if they are currently not installed. Like any other .NET program, you can build your own code custom libraries for use within your Silverlight programs.

A Silverlight application is deployed from a web server as an ‘XAP’ (zip file) package. The XAP file contains the compiled Silverlight assembly, any embedded resources, and any referenced assemblies. The Silverlight runtime downloads the XAP package and executes its contents in web browser.

Once loaded by the plug-in, the SL application is able to make remote calls (to the web server or any arbitrary endpoint) using WCF technologies. The entire web page does *not* need to be refreshed when the SL web plug in changes state. This can greatly enhance the end user experience.

Silverlight architecture is altogether different that WPF, however it tries to implement the features available in WPF. From developer prospective there is no major difference in WPF or Silverlight even though Silverlight CLR is not same as WPF CLR.

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