• User32 provides the familiar Windows look and feel for elements such as windows, buttons, text boxes, and so on.

• GDI/GDI+ provides drawing support for rendering shapes, text, and images at the cost

of additional complexity (and often lackluster performance). Over the years, both technologies have been refined, and the APIs that developers use to interact with them have changed dramatically. But whether you're crafting an application with .NET and Windows Forms, or lingering in the past with Visual Basic 6 or MFC-based C++ code, behind the scenes the same parts of the Windows operating system are at work. Newer frameworks simply deliver better wrappers for interacting with User32 and GDI/GDI+. They can provide improvements in efficiency, reduce complexity, and add prebaked features so you don't have to code them yourself; but they can't remove the fundamental limitations of a system component that was designed more than a decade ago.

Note The basic division of labor between User32 and GDI/GDI+ was introduced more than 15 years ago and was well established in Windows 3.0. Of course, User32 was simply User at that point, because software hadn't yet entered the 32-bit world.

DirectX: The New Graphics Engine

Microsoft created one way around the limitations of the User32 and GDI/GDI+ libraries: DirectX. DirectX began as a cobbled-together, error-prone toolkit for creating games on the Windows platform. Its design mandate was speed, and so Microsoft worked closely with video card vendors to give DirectX the hardware acceleration needed for complex textures, special effects such as partial transparency, and three-dimensional graphics.

Over the years since it was first introduced (shortly after Windows 95), DirectX has matured. It's now an integral part of Windows, with support for all modern video cards. However, the programming API for DirectX still reflects its roots as a game developer's toolkit. Because of its raw complexity, DirectX is almost never used in traditional types of Windows applications (such as business software).

WPF changes all this. In WPF, the underlying graphics technology isn't GDI/GDI+. Instead, it's DirectX. Remarkably, WPF applications use DirectX no matter what type of user interface you create. That means that whether you're designing complex three-dimensional graphics (DirectX's forté) or just drawing buttons and plain text, all the drawing work travels through the DirectX pipeline. As a result, even the most mundane business applications can use rich effects such as transparency and anti-aliasing. You also benefit from hardware acceleration, which simply means DirectX hands off as much work as possible to the GPU (graphics processing unit), which is the dedicated processor on the video card.

Note DirectX is more efficient because it understands higher-level ingredients such as textures and gradients, which can be rendered directly by the video card. GDI/GDI+ doesn't, so it needs to convert them to pixel-by-pixel instructions, which are rendered much more slowly by modern video cards.

One component that's still in the picture (to a limited extent) is User32. That's because 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.

Note 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.

Hardware Acceleration and WPF

You're probably aware that video cards differ in their support for specialized rendering features and optimizations. When programming with DirectX, that's a significant headache. With WPF, it's a much smaller concern, because WPF has the ability to perform everything it does using software calculations rather than relying on built-in support from the video card.

Note There's one exception to WPF's software support. Due to poor driver support, WPF only performs anti-aliasing for 3-D drawings if you're running your application on Windows Vista (and you have a native Windows Vista driver for your video card). That means that if you draw three-dimensional shapes on a Windows XP computer, you'll end up with slightly jagged edges rather than nicely smoothed lines. Anti-aliasing is always provided for 2-D drawings, regardless of the operating system and driver support.

Having a high-powered video card is not an absolute guarantee that you'll get fast, hardware-accelerated performance in WPF. Software also plays a significant role. For example, WPF can't provide hardware acceleration to video cards that are using out-of-date drivers. (If you're using an older video card, these out-of-date drivers are quite possibly the only ones that were provided in the retail package.) WPF also provides better performance under the Windows Vista operating system, where it can take advantage of the new Windows Vista Display Driver Model (WDDM). WDDM offers several important enhancements beyond the Windows XP Display Driver Model (XPDM). Most importantly, WDDM allows several GPU operations to be scheduled at once, and it allows video card memory to be paged to normal system memory if you exceed what's available on the video card.

As a general rule of thumb, WPF offers some sort of hardware acceleration to all WDDM (Windows Vista) drivers and to XPDM (Windows XP) drivers that were created after November 2004, which is when Microsoft released new driver development guidelines. Of course, the level of support differs. When the WPF infrastructure first starts up, it evaluates your video card and assigns it a rating from 0 to 2, as described in the sidebar "WPF Tiers."

Part of the promise of WPF is that you don't need to worry about the details and idiosyncrasies of specific hardware. WPF is intelligent enough to use hardware optimizations where possible, but it has a software fallback for everything. So if you run a WPF application on a computer with a legacy video card, the interface will still appear the way you designed it. Of course, the software alternative may be much slower, so you'll find that computers with older video cards won't run rich WPF applications very well, especially ones that incorporate complex animations or other intense graphical effects. In practice, you might choose to scale down complex effects in the user interface, depending on the level of hardware acceleration that's available in the client (as indicated by the RenderCapability.Tier property).

Note The goal of WPF 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 your computer's CPU). That way, you keep the CPU free for other work, you make the best use of your video card, and you are able to take advantage of performance increases in newer video cards as they become available.