Using Direct2D with WPF

Introduction

With Windows 7, Microsoft introduced a new technology called Direct2D (which is also supported on Windows Vista SP2 with the Platform Update installed). Looking through all its documentation, you'll notice it's aimed at Win32 developers; however, the Windows API Code Pack allows .NET developers to use the features of Windows 7 easily, with Direct2D being one of the features supported. Unfortunately, all the WPF examples included with the Code Pack require hosting the control in a HwndHost, which is a problem as it has airspace issues. This basically means that the Direct2D control needs to be separated from the rest of the WPF controls, which means no overlapping controls with transparency.

The attached code allows Direct2D to be treated as a normal WPF control and, thanks to some COM interfaces, doesn't require you to download the DirectX SDK or even play around with any C++ - the only dependency is the aforementioned Code Pack (the binaries of which are included in the attached). This article is more about the problems found along the way the challenges involved in creating the control, so feel free to skip to the Using the code section if you want to jump right in.

Background

WPF architecture

WPF is built on top of DirectX 9, and uses a retained rendering system. What this means is that you don't draw anything to the screen, but instead create a tree of visual objects; their drawing instructions are cached and later rendered automatically by the framework. This, coupled with using DirectX to do the graphics processing, enables WPF applications not only to remain responsive when they have to be redrawn, but also allows WPF to use a "painter's algorithm" painting model. In this model, each component (starting at the back of the display, going towards the front) is asked to draw itself, allowing them to paint over the previous component's display. This is the reason it's so easy to have complex and/or partially transparent shapes with WPF - because it was designed taking this scenario into account. For more information, check out the MSDN article.

Read more: Codeproject

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