Windows Display Driver Model
Encyclopedia
Windows Display Driver Model (WDDM, also WVDDM during the Vista time-frame) is the graphic driver architecture for video card
drivers
running Microsoft Windows
versions beginning with Windows Vista
.
It is a replacement for the Windows XP display driver architecture aimed at enabling better performance graphics and new graphics functionality.
WDDM provides the functionality required to render the desktop and applications using Desktop Window Manager
, a compositing
window manager
running on top of Direct3D
. It also supports new DXGI interfaces required for basic device management and creation. The WDDM specification requires at least Direct3D 9-capable video card and the display driver must implement the device driver interfaces
for the Direct3D 9Ex runtime in order to run legacy Direct3D applications; it may optionally implement runtime interfaces for Direct3D 10/10.1 and higher.
of video memory into system RAM. In case the video memory available turns out to be insufficient to store all the video data and textures, currently unused data is moved out to system RAM or to the disk. When the swapped out data is needed, it is fetched back. Virtualization could be supported on previous driver models (such as the XP Driver Model) to some extent, but was the responsibility of the driver, instead of being handled at the runtime level.
graphics surface is the memory area that contains information about the textured
mesh
es used for rendering a 2D or 3D scene. WDDM allows Direct3D surfaces to be shared across processes
. Thus, an application can incorporate a mesh created by another application into the scene it is rendering. Sharing textures between processes before WDDM was difficult, as it would have required copying the data from video memory to system memory and then back to video memory for the new device.
Drivers under Windows XP were free to deal with hardware faults as they saw fit either by reporting it to the user or by attempting to recover silently. With a WDDM driver, all hardware faults cause the driver to be reset and the user will be notified by a popup; this unifies the behavior across vendors.
Previous drivers were fully implemented in kernel mode, whereas WDDM is implemented partly in user mode. If the user mode area fails with an unrecoverable error, it will, at the most, cause the application to quit unexpectedly instead of producing a blue screen error
as it would in previous driver models.
WDDM also allows the graphics hardware to be reset or unplugged without a proper reboot. In practice, a driver update should not necessitate a reboot.
. Since the desktop and application windows managed by DWM are Direct3D applications, the number of open windows directly affects the amount of video memory required. Because there is no limit on the number of open windows, the video memory available may prove insufficient, necessitating virtualization. As the window contents that DWM composes into the final desktop are generated by different processes, cross-process surface sharing is necessary. Also, because there can be other DirectX applications running alongside DWM on the DWM-managed desktop, they must be able to access the GPU in a shared manner, necessitating scheduling.
Though this is true for Microsoft's implementation of a composited desktop under Windows Vista, on the other hand, a composited desktop need not theoretically require a new display driver model to work as expected. Successful implementations of composited desktops were done before Windows Vista on other platforms such as Quartz
, Compiz
, WindowFX. The approach Microsoft attempted was to try to make sure WDDM was a unified experience across different GPUs from multiple vendors by standardizing their features and performance. The software features missing from other driver models could be made immaterial by extensions or if a less restrictive or simply different driver model was in place.
s. However, according to Microsoft as of 2009, only about 1-2 percent of hardware used the XPDM, with the rest already WDDM capable. It also requires some other hardware features; consequently some SM 2.0-supporting hardware such as the Intel GMA
900 fails the WDDM certification.
One of the limitations of WDDM driver model version 1.0 is that it does not support multiple drivers in a multi-adapter, multi-monitor setup. If a multi-monitor system has more than one graphics adapter powering the monitors, both the adaptors must use the same WDDM driver. If more than one driver is used, Windows will disable one of them. WDDM 1.1 does not have this limitation.
WDDM 1.0/1.1 does not allow some modes that were previously handled by the driver such as spanning mode (stretching the desktop across two monitors) although Dual View is still available.
Hardware acceleration of GDI and Direct2D/DirectWrite operations helps reduce memory footprint in Windows 7, because DWM compositing engine no longer needs to keep a system memory copy of all surfaces used by GDI/GDI+, as in Windows Vista.
DXGI 1.1, Direct3D 11, Direct2D and DirectWrite were made available with Windows Vista Platform Update; however GDI/GDI+ in Vista continues to rely on software rendering and the Desktop Window Manager
continues to use Direct3D 9Ex.
WDDM 1.1 drivers are backward compatible with WDDM 1.0 specification; both 1.0 and 1.1 drivers can be used in Windows Vista with or without the Platform Update.
includes WDDM 1.2 and DXGI 1.2. New features were first previewed at the Windows BUILD conference and include performance improvements as well as support for stereoscopic 3D
rendering and video playback.
Other major features include finer preemptive multitasking granularity (DMA buffer, primitive, triangle, pixel, or instruction-level), reduced memory footprint, improved resource sharing and faster timeout detection and recovery. 16-bit color surface formats (565, 5551, 4444) are mandatory in Windows 8, and Direct3D 11 Video supports YUV 4:4:4/4:2:2/4:2:0/4:1:1
video formats with 8, 10, and 16-bit precision, as well as 4 and 8-bit palletized formats.
2006, Microsoft talked about how it was planning a major change to WDDM to allow for better multitasking
on GPUs
. According to Microsoft, WDDM 1.0 only allows rudimentary task scheduling with rendering "batch queue" granularity. WDDM 2.0 and WDDM 2.1, which at that time were expected post-Vista but on which Microsoft had not put an introduction date, would offer fine grain preemptive multitasking and would require a new generation of GPUs. Since these features are present in WDDM 1.2, it seems likely that Microsoft elected to use a different version number for the same update.
Video card
A video card, Graphics Card, or Graphics adapter is an expansion card which generates output images to a display. Most video cards offer various functions such as accelerated rendering of 3D scenes and 2D graphics, MPEG-2/MPEG-4 decoding, TV output, or the ability to connect multiple monitors...
drivers
Device driver
In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
running Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
versions beginning with Windows Vista
Windows Vista
Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
.
It is a replacement for the Windows XP display driver architecture aimed at enabling better performance graphics and new graphics functionality.
WDDM provides the functionality required to render the desktop and applications using Desktop Window Manager
Desktop Window Manager
Desktop Window Manager is the window manager in Windows Vista and Windows 7 that enables the Windows Aero graphical user interface and visual theme. The Desktop Window Manager requires video cards supporting DirectX 9.0 and Shader Model 2.0. DWM is not included with Windows Vista Starter edition...
, a compositing
Compositing window manager
A compositing window manager is a type of window manager. A window manager is software that draws a graphical user interface on a computer display – it positions windows, draws additional elements on windows , and controls how windows interact with each other, and with the rest of the desktop...
window manager
Window manager
A window manager is system software that controls the placement and appearance of windows within a windowing system in a graphical user interface. Most window managers are designed to help provide a desktop environment...
running on top of Direct3D
Direct3D
Direct3D is part of Microsoft's DirectX application programming interface . Direct3D is available for Microsoft Windows operating systems , and for other platforms through the open source software Wine. It is the base for the graphics API on the Xbox and Xbox 360 console systems...
. It also supports new DXGI interfaces required for basic device management and creation. The WDDM specification requires at least Direct3D 9-capable video card and the display driver must implement the device driver interfaces
Device driver
In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
for the Direct3D 9Ex runtime in order to run legacy Direct3D applications; it may optionally implement runtime interfaces for Direct3D 10/10.1 and higher.
Features enabled by the WDDM
WDDM drivers enable new areas of functionality which were not uniformly provided by earlier display driver models. These include:Virtualized video memory
In the context of graphics, virtualization means that individual processes (in user mode) cannot see the memory of adjacent processes even by means of insertion of forged commands in the command stream. WDDM drivers allow video memory to be virtualized, and video data to be paged outPaging
In computer operating systems, paging is one of the memory-management schemes by which a computer can store and retrieve data from secondary storage for use in main memory. In the paging memory-management scheme, the operating system retrieves data from secondary storage in same-size blocks called...
of video memory into system RAM. In case the video memory available turns out to be insufficient to store all the video data and textures, currently unused data is moved out to system RAM or to the disk. When the swapped out data is needed, it is fetched back. Virtualization could be supported on previous driver models (such as the XP Driver Model) to some extent, but was the responsibility of the driver, instead of being handled at the runtime level.
Scheduling
The runtime handles scheduling of concurrent graphics contexts. Each list of commands is put in a queue for execution by the GPU, and it can be preempted by the runtime if a more critical task arrives and if it has not begun execution. This differs from native threads on the CPU where one task cannot be interrupted and therefore can take longer than necessary and make the computer appear less responsive. A hybrid scheduling algorithm between native and light threads with cooperation between the threads would achieve seamless parallelism. It is important to note that scheduling is not a new concept but it was previously the responsibility of individual driver developers. WDDM attempts to unify the experience across different vendors by controlling the execution of GPU tasks.Cross-process sharing of Direct3D surfaces
A Direct3DDirect3D
Direct3D is part of Microsoft's DirectX application programming interface . Direct3D is available for Microsoft Windows operating systems , and for other platforms through the open source software Wine. It is the base for the graphics API on the Xbox and Xbox 360 console systems...
graphics surface is the memory area that contains information about the textured
Procedural texture
A procedural texture is a computer generated image created using an algorithm intended to create a realistic representation of natural elements such as wood, marble, granite, metal, stone, and others....
mesh
Mesh
Mesh consists of semi-permeable barrier made of connected strands of metal, fiber, or other flexible/ductile material. Mesh is similar to web or net in that it has many attached or woven strands.-Types of mesh:...
es used for rendering a 2D or 3D scene. WDDM allows Direct3D surfaces to be shared across processes
Process (computing)
In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system , a process may be made up of multiple threads of execution that execute instructions concurrently.A computer program is a...
. Thus, an application can incorporate a mesh created by another application into the scene it is rendering. Sharing textures between processes before WDDM was difficult, as it would have required copying the data from video memory to system memory and then back to video memory for the new device.
Enhanced fault-tolerance
If a WDDM driver hangs or encounters a fault, the graphics stack will restart the driver. A graphics hardware fault will be intercepted and if necessary the driver will be reset.Drivers under Windows XP were free to deal with hardware faults as they saw fit either by reporting it to the user or by attempting to recover silently. With a WDDM driver, all hardware faults cause the driver to be reset and the user will be notified by a popup; this unifies the behavior across vendors.
Previous drivers were fully implemented in kernel mode, whereas WDDM is implemented partly in user mode. If the user mode area fails with an unrecoverable error, it will, at the most, cause the application to quit unexpectedly instead of producing a blue screen error
Blue Screen of Death
To forse a BSOD Open regedit.exe,Then search: HKLM\SYSTEM\CurrentControlSet\services\i8042prt\ParametersThen make a new DWORD called "CrashOnCtrlScroll" And set the value to 1....
as it would in previous driver models.
WDDM also allows the graphics hardware to be reset or unplugged without a proper reboot. In practice, a driver update should not necessitate a reboot.
Need for a new display driver model
One of the chief scenarios the Windows Display Driver Model enables is the Desktop Window ManagerDesktop Window Manager
Desktop Window Manager is the window manager in Windows Vista and Windows 7 that enables the Windows Aero graphical user interface and visual theme. The Desktop Window Manager requires video cards supporting DirectX 9.0 and Shader Model 2.0. DWM is not included with Windows Vista Starter edition...
. Since the desktop and application windows managed by DWM are Direct3D applications, the number of open windows directly affects the amount of video memory required. Because there is no limit on the number of open windows, the video memory available may prove insufficient, necessitating virtualization. As the window contents that DWM composes into the final desktop are generated by different processes, cross-process surface sharing is necessary. Also, because there can be other DirectX applications running alongside DWM on the DWM-managed desktop, they must be able to access the GPU in a shared manner, necessitating scheduling.
Though this is true for Microsoft's implementation of a composited desktop under Windows Vista, on the other hand, a composited desktop need not theoretically require a new display driver model to work as expected. Successful implementations of composited desktops were done before Windows Vista on other platforms such as Quartz
Quartz (graphics layer)
Quartz specifically refers to a pair of Mac OS X technologies, each part of the Core Graphics framework: Quartz 2D and Quartz Compositor. It includes both a 2D renderer in Core Graphics and the composition engine that sends instructions to the graphics card...
, Compiz
Compiz
Compiz is one of the first compositing window managers for the X Window System that uses 3D graphics hardware to create fast compositing desktop effects for window management. The effects, such as a minimization effect and a cube workspace are implemented as loadable plugins...
, WindowFX. The approach Microsoft attempted was to try to make sure WDDM was a unified experience across different GPUs from multiple vendors by standardizing their features and performance. The software features missing from other driver models could be made immaterial by extensions or if a less restrictive or simply different driver model was in place.
Limitations
The new driver model requires the graphics hardware to have Shader Model 2.0 support at least, since the fixed function pipeline is now translated to 2.0 shaderShader
In the field of computer graphics, a shader is a computer program that is used primarily to calculate rendering effects on graphics hardware with a high degree of flexibility...
s. However, according to Microsoft as of 2009, only about 1-2 percent of hardware used the XPDM, with the rest already WDDM capable. It also requires some other hardware features; consequently some SM 2.0-supporting hardware such as the Intel GMA
Intel GMA
The Intel Graphics Media Accelerator, or GMA, is a series of Intel integrated graphics processors built into various motherboard chipsets....
900 fails the WDDM certification.
One of the limitations of WDDM driver model version 1.0 is that it does not support multiple drivers in a multi-adapter, multi-monitor setup. If a multi-monitor system has more than one graphics adapter powering the monitors, both the adaptors must use the same WDDM driver. If more than one driver is used, Windows will disable one of them. WDDM 1.1 does not have this limitation.
WDDM 1.0/1.1 does not allow some modes that were previously handled by the driver such as spanning mode (stretching the desktop across two monitors) although Dual View is still available.
WDDM 1.1
Windows 7 supports major additions to WDDM known as WDDM 1.1; the details of this new version were unveiled at WinHEC 2008. New features include:- DXGIDXGIDirectX Graphics Infrastructure is a user-mode component of Windows Vista and above which provides a mapping between particular graphics APIs such as Direct3D 10.0 and above and the graphics kernel, which in turn interfaces with the user-mode Windows Display Driver Model driver...
1.1, which features return of hardware 2D2D computer graphics2D computer graphics is the computer-based generation of digital images—mostly from two-dimensional models and by techniques specific to them...
acceleration for use by GDIGraphics Device InterfaceThe Graphics Device Interface is a Microsoft Windows application programming interface and core operating system component responsible for representing graphical objects and transmitting them to output devices such as monitors and printers....
(but not GDI+) and Direct2DDirect2DDirect2D is a 2D and vector graphics application programming interface designed by Microsoft and implemented in Windows 7 and Windows Server 2008 R2, and also Windows Vista and Windows Server 2008 and Platform Update Supplement for Windows Vista and for Windows Server 2008 & KB2505189 update...
/DirectWriteDirectWriteDirectWrite is a text-layout and glyph-rendering API by Microsoft. It was designed to replace GDI/GDI+ and Uniscribe for screen-oriented rendering and was shipped with Windows 7 and Windows Server 2008 R2, as well as Windows Vista and Windows Server 2008 DirectWrite is a text-layout and...
- BitBltBit blitBit BLIT is a computer graphics operation in which several bitmaps are combined into one using a raster operator....
, StretchBlt, TransparentBlt - AlphaBlend, ColorFill
- ClearTypeClearTypeClearType is a trademark for Microsoft's implementation of subpixel rendering technology. ClearType attempts to improve the appearance of text on certain types of computer display screens by sacrificing color fidelity for additional intensity variation. This trade-off is asserted to work well on...
font support
- BitBlt
- Direct3D 11 Device Driver Interface (DDIDevice driverIn computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
) - DXVA-HD DDI
- Hardware video overlayHardware overlayIn computing, hardware overlay, a type of video overlay, provides a method of rendering an image to a display screen with a dedicated memory buffer inside computer video hardware. The technique aims to improve the display of a fast-moving video image — such as a computer game, a DVD, or the signal...
DDI - Optional AES 128 encryption
- Optional decoding of encrypted video content
- Support multiple drivers in a multi-adapter and multi-monitor setup
Hardware acceleration of GDI and Direct2D/DirectWrite operations helps reduce memory footprint in Windows 7, because DWM compositing engine no longer needs to keep a system memory copy of all surfaces used by GDI/GDI+, as in Windows Vista.
DXGI 1.1, Direct3D 11, Direct2D and DirectWrite were made available with Windows Vista Platform Update; however GDI/GDI+ in Vista continues to rely on software rendering and the Desktop Window Manager
Desktop Window Manager
Desktop Window Manager is the window manager in Windows Vista and Windows 7 that enables the Windows Aero graphical user interface and visual theme. The Desktop Window Manager requires video cards supporting DirectX 9.0 and Shader Model 2.0. DWM is not included with Windows Vista Starter edition...
continues to use Direct3D 9Ex.
WDDM 1.1 drivers are backward compatible with WDDM 1.0 specification; both 1.0 and 1.1 drivers can be used in Windows Vista with or without the Platform Update.
WDDM 1.2
Windows 8Windows 8
Windows 8 is the codename for the next version of the Microsoft Windows computer operating system following Windows 7. It has many changes from previous versions. In particular it adds support for ARM microprocessors in addition to the previously supported x86 microprocessors from Intel and AMD...
includes WDDM 1.2 and DXGI 1.2. New features were first previewed at the Windows BUILD conference and include performance improvements as well as support for stereoscopic 3D
Stereoscopy
Stereoscopy refers to a technique for creating or enhancing the illusion of depth in an image by presenting two offset images separately to the left and right eye of the viewer. Both of these 2-D offset images are then combined in the brain to give the perception of 3-D depth...
rendering and video playback.
Other major features include finer preemptive multitasking granularity (DMA buffer, primitive, triangle, pixel, or instruction-level), reduced memory footprint, improved resource sharing and faster timeout detection and recovery. 16-bit color surface formats (565, 5551, 4444) are mandatory in Windows 8, and Direct3D 11 Video supports YUV 4:4:4/4:2:2/4:2:0/4:1:1
Chroma subsampling
Chroma subsampling is the practice of encoding images by implementing less resolution for chroma information than for luma information, taking advantage of the human visual system's lower acuity for color differences than for luminance....
video formats with 8, 10, and 16-bit precision, as well as 4 and 8-bit palletized formats.
WDDM 2.0
At WinHECWindows Hardware Engineering Conference
The Windows Hardware Engineering Conference is the annual software and hardware developer-oriented trade show and business conference where Microsoft elaborates on its hardware plans for Microsoft Windows-compatible PCs...
2006, Microsoft talked about how it was planning a major change to WDDM to allow for better multitasking
Computer multitasking
In computing, multitasking is a method where multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is actively executing instructions for...
on GPUs
Graphics processing unit
A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...
. According to Microsoft, WDDM 1.0 only allows rudimentary task scheduling with rendering "batch queue" granularity. WDDM 2.0 and WDDM 2.1, which at that time were expected post-Vista but on which Microsoft had not put an introduction date, would offer fine grain preemptive multitasking and would require a new generation of GPUs. Since these features are present in WDDM 1.2, it seems likely that Microsoft elected to use a different version number for the same update.