Windows Presentation Foundation: What, Why and When
A. WHY WPF: WPF is framework to build
application for windows. It is designed for .NET influenced by modern display
technologies like HTML and Flash and hardware acceleration.
Don't take WPF as
replacement for window forms which has been hot favorite for developers like us
for building application for windows.
1. Life before WPF:
It will be inevitable
not to look back and see what a standard windows application replies on two
well worn parts of windows operation system to create its user interface.
a) User32:
provides familiar windows look and feel for element.
b) GDI/GDI +: provides
drawing support for rendering shapes, text, images etc,
Newer framework
just provides a wrapper to interacting with User32 or GDI. These API as
wrappers just provide improvement in efficiently, reduce complexity.
The
problem with User32 and GDI are that they are designed decade back and couldn't
catch up well with advancement of hardware
i.e. graphics card, introduction to high resolution screens. So we were still
using a decade old technology and with on growing hardware. So Microsoft
created one way around the limitations of the User32 and GDI/GDI+ libraries: DirectX,
which was used for creating games on the windows platform. The ultimate purpose
was to give hardware acceleration to DirectX from video card of computer, to
compute complex textures, special effects, some special effects, 3D graphics
etc.
Problem
with DirectX was that due to its raw complexity, it was almost never used in
traditional types of Windows applications (such as business software).
Another
factor which window forms based on above named technologies suffered was resolution.
Traditional
Windows applications are bound by certain assumptions about resolution. We usually
assume a standard monitor resolution (such as 1024 by 768 pixels), design our windows
with that in mind, and try to ensure reasonable resizing behavior for smaller
and larger dimensions
2. Wind of Change, WPF: WPF changes all this and is
fundamentally different from window forms. WPF's underlying technology isn't GDI/GDI+,
instead it uses DirectX. So WPF uses DirectX no matter what type of user
interface we create. So it's like whether we are creating complex 3D graphics
or just drawing a button , all the drawing work have to pass through DirectX
pipeline. Since WPF relies on DirectX, now we can take advantage of hardware
acceleration as well , which means this will hand off much work as possible to
the GPU(graphics processing unit ) which is dedicated processor on video card,
and our CPU(central processing unit ) could do some rest. J
3. Do WPF rely on User32? WPF still relies on User32 for certain
services, such as handling and routing input and sorting out which application
owns which portion of screen real estate. However, all the drawing is funneled
through DirectX.
This is the most
significant change in WPF. WPF is not a wrapper for GDI/GDI+. Instead,
it's a replacement-a separate layer that works through DirectX.
4. What does it means" hardware
acceleration": It is to offload as much of the work as
possible on the video card so that complex graphics routines are render-bound
(limited by the GPU) rather than processor-bound (limited by our
computer's CPU). That way, we keep the CPU free for other work, we make the
best use of our video card, and we are able to take advantage of performance
increases in newer video cards as they become available.
5. How Hardware acceleration is achieved
with WPF: WPF is
intelligent enough to use hardware optimizations where possible by the use of
drivers, but it has a software fallback for everything. So if we run a WPF
application on a computer with a legacy video card, the interface will still
appear the way we designed it. Of course, the software alternative may be much
slower, so we'll find that computers with older video cards won't run rich WPF
applications very well.
6. Resolution independence: The problem with the user interface
in traditional Windows applications that they aren't scalable. As a result, if we
use a high monitor resolution that crams pixels in more densely, our application
windows become smaller and more difficult to read. This is particularly a
problem with newer monitors that have high pixel densities and run at
correspondingly high resolutions.
WPF doesn't
suffer from this problem because it renders all user interface elements itself,
from simple shapes to common controls such as buttons. As a result, if we
create a button that's 1 inch wide on our computer monitor, it can remain 1
inch wide on a high-resolution monitor-WPF will simply render it in greater
detail and with more pixels. Most importantly, we need to realize that WPF
bases it's scaling on the system DPI setting, not the DPI of our
physical display device.
So how does WPF
determine how big an application window should be? The short answer is
that WPF uses the system DPI setting when it calculates sizes.
7. Not possible to integrate or overlap
technologies like User32, GDI, DirectX ,Flash etc.
One of the
challenges of the desktop world is with these technologies is of mixing them altogether.
Infact whatever shortcoming which discussed above in the article already has
the solutions before WPF come into the picture. Say wants to get design ability
benefit of web, well we nobody is stopping using HTML in desktop applications. Want
scalable animated graphics, well flash does that and we can use it in our
desktop application. Need support of accessibility in the software, well Win32 do
the work for us? And when it comes to take full advantage of graphics hardware,
well we can use DirectX.
But the problem
arises when we need some combination of these features; say I want to use visual
capability of flash with accessibility usability of classic Win32; well it's
tough to do. Need to put Wind32 buttons listbox inside DirectX scene, well
tough m we can't do that.
Problem here is
that each of these technologies is isolated, we can combine these technologies,
but we have to partition our screen, so that areas rendered by DirectX do not
overlap area rendered by HTML. We can make flash content overlap with HTML, but
there is issue of visual handling, we do not get proper overlap, there is some
hack. And in general we can't apply element of one technology to a different technology,
there is no any integration across these pieces.
WPF solves this,
as it is described as single integrated solution. Its unique feature is
integration of all these unique features technologies, i.e. this composibility is single best feature.
B. WHAT is WPF? A high level API:
WPF is the
beginning of the future of Windows development. In time, it will become a system
like User32 and GDI/GDI+, on top of which more enhancements and higher-level features
are added.
1. WPF Evolution: WPF exists in two versions:
a. WPF 3.0: Along
with WCF, WWF all three together were called the .NET framework 3.0
b. WPF 3.5: These
have minor refinement with some bug fixing and performance improvement.
c. WPF 4.0:
Differences between
3.0 and 3.5 are below;
a. Significant
difference between WPF 3.0 and 3.5 is design-time support.
b. The .NET Framework
3.0 was released without a corresponding version of Visual Studio. The .NET
Framework 3.5 was released in conjunction with Visual Studio 2008, and as a result,
it offers much better design-time support for building WPF applications.
2. Visual Studio support and WPF: Visual Studio 2008 allows us to create applications that are
specifically designed to work with .NET 2.0, .NET 3.0, or .NET 3.5.
To understand how
the Visual Studio multitargeting
system works, we need to know a bit more about how .NET 3.5 is structured. Essentially,
.NET 3.5 is built out of three separate pieces-a copy of the original .NET 2.0
assemblies, a copy of the assemblies that were added in .NET 3.0 (for WPF, WCF,
and WF), and the new assemblies that were added in .NET 3.5 (for LINQ and a
number of miscellaneous features). However, when we create and test an
application in Visual Studio, we are always using the .NET 3.5 assemblies. When
we choose to target an earlier version of .NET, Visual Studio simply uses a
subset of the .NET 3.5 assemblies.
3. WPF Architecture: WPF uses a multilayered architecture.
At the top, our 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.
Let us discuss in detail about role of each DLL classes.
1. 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 we'll use directly come from this assembly.
2. PresentationCore.dll
holds base types, such as UIElement and Visual, from which all shapes and
controls derive. If we don't need the full window and control abstraction layer,
we can drop down to this level and still take advantage of WPF's rendering engine.
3. 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.
4. 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.
5. WindowsCodecs.dll
is a low-level
API that provides imaging support (for example, processing, displaying, and
scaling bitmaps and JPEGs).
6. Direct3D is
the low-level API through which all the graphics in a WPF are rendered.
7. 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.
4. WPF some features: If the only thing WPF offered was
hardware acceleration through DirectX, it would be a compelling improvement,
but not a revolutionary one. But WPF actually includes a basket of high-level
services designed for application programmers.
a. A web-like layout
model. Rather than fix controls in place with specific coordinates, WPF
emphasizes flexible flow layout that
arranges controls based on their content. The result is a user interface that
can adapt to show highly dynamic content or different languages.
b. A rich
drawing model. Rather than painting pixels, in WPF we deal with primitives-basic
shapes, blocks of text, and other graphical ingredients. We also have new
features, such as true transparent controls, the ability to stack multiple
layers with different opacities, and native 3-D support.
c. Animation
as a first-class programming concept. Yes, we could use a timer to force a form
to repaint it. But in WPF, animation is an intrinsic part of the framework. We define
animations with declarative tags, and WPF puts them into action automatically
d. Styles and
templates. Styles allow us to standardize formatting and reuse it
throughout our application. Templates allow us to change the way any element is
rendered, even a core control such as the button. It's never been easier to
build modern skinned interfaces.
e. Page-based
applications. Using WPF, we can build a browser-like application that lets we
move through a collection of pages, complete with forward and back navigation buttons.
WPF handles the messy details, such as the page history. We can even deploy our
project as a browser-based application that runs right inside Internet Explorer.
C. WHEN to use WPF: WPF is the platform for the future of
Windows user interface development. However, it won't displace Windows Forms
overnight. Windows Forms is in many ways the culmination of the display
technology built on GDI/GDI+ and User32. It's more mature than WPF and still includes
features that haven't made their way into the WPF toolkit (such as the
WebBrowser control, the DataGridView control, and the HelpProvider component).
So which platform
should we choose when we begin designing a new Windows application?
a. If we are
starting from the ground up, WPF is an ideal choice and it offers the best
prospects for future enhancements and longevity.
b. Similarly, if we
need one of the features that WPF provides and Windows Forms does not-such as 3D
drawing or page-based applications-it makes sense to make the shift. On the
other hand, if we have a considerable investment in a Windows Forms-based
business application, there's no need to recode our efforts.
c. WPF is an
especially great platform to use if our applications involve various media
types. For example, if we need to
incorporate video, or documents, or 3D content, or animated transitions between
a sequence of images, or a combination of any of the above.
d. WPF is also great if we need to create a skinned user interface,
or if we need to bind to XML data, or dynamically load portions of a user
interface from a Web service, or want to create a desktop application with a
Web-like navigation style.
e. If we are building applications with no need for the extensive
modern functionality in WPF, then there is no compelling reason to leave behind
a time-tested developer-approved platform like WinForms
f. Lastly, don't
forget that it is possible to use WPF controls in a WinForms app, and WinForms
controls in a WPF app. If we have a substantial investment in a WinForms
code-base, but want to use some aspect(s) of WPF, we can leverage the interop
support to make that possible.
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reading
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