An initial investigation into WDDM on ReactOS

Summary

The history of ReactOS spans a wider range than the lives of many of the people who work on it today. Incredible individuals have come and gone from the project with vastly different goals for what they want to see developed. In recent years, better hardware support has emerged as one of those goals. As ReactOS gazes towards the world of Vista and beyond, a few questions about how hardware works emerge. Vista introduced massive overhauls to how hardware drivers are written and maintained. Gradually we’re trying to handle many of these overhauls with great success. Today we talk about WDDM, or the Windows Display Driver Model. The “Overhaul” I’ve always found the video driver documentation lacking for both architectures, enough to get started but not really enough to get deep into the world of 3D. Thankfully in recent years this has changed enough to where some open-source drivers have popped up. WDDM is a major overhaul that shifts responsibility of managing the GPU away from Win32k and gives better control over the GPU to the driver vendor. Dxgkrnl.sys, the DirectX graphics driver, talks to a miniport driver to provide varying levels of WDDM interfaces. The WDDM revision (WDDM 1.0, 1.1, 1.2….) primarily describes how many of these interfaces are supported and implemented. This is different than the feature level that is described in DxDiag. DxDiag on Windows 10 Wait… What happened to XDDM? Officially starting with Windows 8, every GPU driver for the system had to be a WDDM driver. But all that was really dropped was the miniport driver. Vista and 7 could still load older GPU drivers using the XDDM architecture without complaint. Outside of the miniport driver, modern Windows still has XDDM remnants all over the place, including mechanisms for WDDM. The first example of this came when trying to load OpenGL installable client drivers (ICDs) from Vista, or loading our ICDs on Vista, 7, 8, and so on. For WDDM, the communication back to the miniport driver is more direc...