Direct3D is part of Microsoft's DirectX application programming interface (API). Direct3D is available for Microsoft Windows operating systems (Windows 95 and above), 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. Direct3D is used to render three dimensional graphics in applications where performance is important, such as games. Direct3D also allows applications to run fullscreen instead of embedded in a window, though they can still run in a window if programmed for that feature. Direct3D uses hardware acceleration if it is available on the graphics card, allowing for hardware acceleration of the entire 3D rendering pipeline or even only partial acceleration. Direct3D exposes the advanced graphics capabilities of 3D graphics hardware, including z-buffering, spatial anti-aliasing, alpha blending, mipmapping, atmospheric effects, and perspective-correct texture mapping. Integration with other DirectX technologies enables Direct3D to deliver such features as video mapping, hardware 3D rendering in 2D overlay planes, and even sprites, providing the use of 2D and 3D graphics in interactive media ties.
Direct3D is a 3D API. That is, it contains many commands for 3D rendering; however, since version 8, Direct3D has superseded the old DirectDraw framework and also taken responsibility for the rendering of 2D graphics. Microsoft strives to continually update Direct3D to support the latest technology available on 3D graphics cards. Direct3D offers full vertex software emulation but no pixel software emulation for features not available in hardware. For example, if software programmed using Direct3D requires pixel shaders and the video card on the user's computer does not support that feature, Direct3D will not emulate it, although it will compute and render the polygons and textures of the 3D models, albeit at a usually degraded quality and performance compared to the hardware equivalent. The API does include a Reference Rasterizer (or REF device), which emulates a generic graphics card in software, although it is too slow for most real-time 3D applications and is typically only used for debugging. A new real-time software rasterizer, WARP, designed to emulate complete feature set of Direct3D 10.1, is included with Windows 7 and Windows Vista Service Pack 2 with the Platform Update; its performance is said to be on par with lower-end 3D cards on multi-core CPUs.
Direct3D's main competitor is OpenGL. There are many features and issues that proponents of either API disagree over, see Comparison of OpenGL and Direct3D for a summary. Attempts by Microsoft and SGI to unify OpenGL and Direct3D were undertaken in the 1990s, but eventually halted.
- 1 History
- 2 Architecture
- 3 Pipeline
- 4 Feature levels
- 5 Direct3D Mobile
- 6 Related tools
- 7 Wine
- 8 Direct3D and Windows Vista
- 9 See also
- 10 References
- 11 External links
In 1992, Servan Keondjian started a company named RenderMorphics, which developed a 3D graphics API named Reality Lab, which was used in medical imaging and CAD software. Two versions of this API were released. Microsoft bought RenderMorphics in February 1995, bringing Keondjian on board to implement a 3D graphics engine for Windows 95. This resulted in the first version of Direct3D that shipped in DirectX 2.0 and DirectX 3.0.
Direct3D initially implemented "retained mode" and "immediate mode" 3D APIs. The retained mode was a COM-based scene graph API that attained little adoption. Game developers clamored for more direct control of the hardware's activities than the Direct3D retained mode could provide. Only two games that sold a significant volume, Lego Island and Lego Rock Raiders, were based on the Direct3D retained mode, so Microsoft did not update the retained mode after DirectX 3.0.
The first version of Direct3D immediate mode was based on an "execute buffer" programming model that Microsoft hoped hardware vendors would support directly. Execute buffers were intended to be allocated in hardware memory and parsed by the hardware in order to perform the 3D rendering. They were extremely awkward to program, however, hindering adoption of the new API and stimulating calls for Microsoft to adopt OpenGL as the official 3D rendering API for games as well as workstation applications. (see OpenGL vs. Direct3D)
Rather than adopt OpenGL as a gaming API, Microsoft chose to continue improving Direct3D, not only to be competitive with OpenGL, but to compete more effectively with proprietary APIs such as 3dfx's Glide. A team in Redmond took over development of the Direct3D Immediate mode, while Servan's RenderMorphics team continued work on the Retained mode.
Direct3D 4 was the version of Direct3D that included changes for Microsoft's Talisman project, a novel 3D hardware spec which used sprite-based image composition as a way to boost 3D rendering performance. The basic idea behind Talisman was to render separate 3D objects to offscreen render buffers, and then compose those 2D "sprites" back into the main scene. The primary goal of this approach was that individual objects could be re-used over and over again, which lightens the load dramatically on the 3D rendering hardware. Unfortunately, hardware vendors at the time backed out from adopting the Talisman design and instead chose a brute force approach to improve raw performance of more traditional 3D rendering hardware. As a result, the Talisman project was cancelled before any hardware was sold to the public.
In order to support Talisman, the necessary improvement to Direct3D was the SetRenderTarget API. This API allowed rendering 3D objects to arbitrary offscreen surfaces, rather than being fixed only to the backbuffer. That newly rendered surface could then be used as a texture, allowing for complex, multi-stage effects. Although Talisman, and Direct3D 4, never shipped, this API revolutionized the capabilities of 3D hardware, and is the basis of almost every 3D visual effect to this day. At the time, though, not all hardware vendors had designs that could support SetRenderTarget, so adoption was not immediate and universal. The challenge for some hardware vendors were hard-coded designs that separated texture memory from backbuffer memory. It's interesting to note that some hardware vendors, who were quite dominant in the industry at the time but refused to change their designs, ultimately went out of business.
At the time, many other changes to Direct3D were taking place, such as support for compressed textures. However, since Direct3D 4 was never released, those features would have to wait until the release of Direct3D 5.
Hardware vendors worked closely with Microsoft on new features like SetRenderTarget and texture compression, and were forced to add vendor-specific extensions to their OpenGL drivers. This is noteworthy because there was a war raging between Direct3D and OpenGL and prior to this, OpenGL had a stronghold in the industry. Direct3D was arguably more flexible in terms of what hardware it supported, but it's required method of having to check "capability bits" was disliked and even ridiculed. However, the eventual proliferation of vendor-specific extensions in OpenGL rendered the argument someone moot.
Direct3D 5 to 9
Direct3D 5.0 introduced the DrawPrimitive API that eliminated the need for applications to construct execute buffers.
Direct3D 6.0 introduced numerous features to cover contemporary hardware (such as multitexture and stencil buffers) as well as optimized geometry pipelines for x87, SSE and 3DNow! and optional texture management to simplify programming. Direct3D 6.0 also included support for features that had been licensed by Microsoft from specific hardware vendors for inclusion in the API, in exchange for the time-to-market advantage to the licensing vendor. S3 texture compression support was one such feature, renamed as DXTC for purposes of inclusion in the API. Another was TriTech's proprietary bump mapping technique. Microsoft included these features in DirectX, then added them to the requirements needed for drivers to get a Windows logo to encourage broad adoption of the features in other vendors' hardware.
Direct3D 7.0 introduced the .dds texture format and support for transform and lighting hardware acceleration (first available on PC hardware with Nvidia's GeForce), as well as the ability to allocate vertex buffers in hardware memory. Hardware vertex buffers represent the first substantive improvement over OpenGL in DirectX history. Direct3D 7.0 also augmented DirectX support for multitexturing hardware, and represents the pinnacle of fixed-function multitexture pipeline features: although powerful, it was so complicated to program that a new programming model was needed to expose the shading capabilities of graphics hardware.
Direct3D 8.0 introduced programmability in the form of vertex and pixel shaders, enabling developers to write code without worrying about superfluous hardware state. The complexity of the shader programs depended on the complexity of the task, and the display driver compiled those shaders to instructions that could be understood by the hardware. Direct3D 8.0 and its programmable shading capabilities were the first major departure from an OpenGL-style fixed-function architecture, where drawing is controlled by a complicated state machine. Direct3D 8.0 also eliminated DirectDraw as a separate API. Direct3D subsumed all remaining DirectDraw API calls still needed for application development, such as Present(), the function used to display rendering results.
Direct3D was not considered to be user friendly, but as of DirectX version 8.1, many usability problems were resolved. Direct3D 8 contained many powerful 3D graphics features, such as vertex shaders, pixel shaders, fog, bump mapping and texture mapping.
Direct3D 9.0 added a new version of the High Level Shader Language, support for floating-point texture formats, Multiple Render Targets, and texture lookups in the vertex shader. An extension only available in Windows Vista, called Direct3D 9Ex (previously versioned 9.0L), allows the use of the advantages offered by Windows Vista's Windows Display Driver Model (WDDM) and is used for Windows Aero. Direct3D 9Ex, in conjunction with DirectX 9 class WDDM drivers allows graphics memory to be virtualized and paged out to system memory, allows graphics operations to be interrupted and scheduled and allow DirectX surfaces to be shared across processes. Direct3D 9.0Ex was previously known as version 1.0 of Windows Graphics Foundation (WGF).
Windows Vista includes a major update to the Direct3D API. Originally called WGF 2.0 (Windows Graphics Foundation 2.0), then DirectX 10 and DirectX Next, Direct3D 10 features an updated shader model 4.0 and optional interruptibility for shader programs. In this model shaders still consist of fixed stages as on previous versions, but all stages support a nearly unified interface, as well as a unified access paradigm for resources such as textures and shader constants. The language itself has been extended to be more expressive, including integer operations, a greatly increased instruction count, and more C-like language constructs. In addition to the previously available vertex and pixel shader stages, the API includes a geometry shader stage that breaks the old model of one vertex in/one vertex out, to allow geometry to actually be generated from within a shader, allowing for complex geometry to be generated entirely on the graphics hardware.
Windows XP does not support DirectX 10 and above.
Unlike prior versions of the API, Direct3D 10 no longer uses "capability bits" (or "caps") to indicate which features are supported on a given graphics device. Instead, it defines a minimum standard of hardware capabilities which must be supported for a display system to be "Direct3D 10 compatible". This is a significant departure, with the goal of streamlining application code by removing capability-checking code and special cases based on the presence or absence of specific capabilities.
Because Direct3D 10 hardware was comparatively rare after the initial release of Windows Vista and because of the massive installed base of non-Direct3D 10 compatible graphics cards, the first Direct3D 10-compatible games still provide Direct3D 9 render paths. Examples of such titles are games originally written for Direct3D 9 and ported to Direct3D 10 after their release, such as Company of Heroes, or games originally developed for Direct3D 9 with a Direct3D 10 path retrofitted later in development, such as Hellgate: London or Crysis.
The DirectX 10 SDK became available in February 2007.
- Fixed pipelines are being done away with in favor of fully programmable pipelines (often referred to as unified pipeline architecture), which can be programmed to emulate the same.
- New state object to enable (mostly) the CPU to change states efficiently.
- Shader model 4.0 enhances the programmability of the graphics pipeline. It adds instructions for integer and bitwise calculations.
- Geometry shaders, which work on adjacent triangles which form a mesh.
- Texture arrays enable swapping of textures in GPU without CPU intervention.
- Predicated Rendering allows drawing calls to be ignored based on some other conditions. This enables rapid occlusion culling, which prevents objects from being rendered if it is not visible or too far to be visible.
- Instancing 2.0 support, allowing multiple instances of similar meshes, such as armies, or grass or trees, to be rendered in a single draw call, reducing the processing time needed for multiple similar objects to that of a single one.
Direct3D 10.1 was announced by Microsoft shortly after the release of Direct3D 10 as a minor update. The specification was finalized with the release of November 2007 DirectX SDK and the runtime was shipped with the Windows Vista SP1, which is available since mid-March 2008.
Direct3D 10.1 sets a few more image quality standards for graphics vendors, and gives developers more control over image quality. Features include finer control over anti-aliasing (both multisampling and supersampling with per sample shading and application control over sample position) and more flexibilities to some of the existing features (cubemap arrays and independent blending modes). Direct3D 10.1 level hardware must support the following features:
Unlike Direct3D 10 which strictly required Direct3D 10-class hardware and driver interfaces, Direct3D 10.1 runtime can run on Direct3D 10.0 hardware using a concept of "feature levels", but new features are supported exclusively by new hardware which expose feature level 10_1.
The only available Direct3D 10.1 hardware as of June 2008 were the Radeon HD 3000 series and Radeon HD 4000 series from ATI; in 2009, they were joined by Chrome 430/440GT GPUs from S3 Graphics and select lower-end models in GeForce 200 series from Nvidia. In 2011, Intel chipsets started supporting Direct3D 10.1 with the introduction of Intel HD Graphics 2000 (GMA HD).
Direct3D 11 was released as part of Windows 7. It was presented at Gamefest 2008 on July 22, 2008 and demonstrated at the Nvision 08 technical conference on August 26, 2008. AMD previewed working DirectX11 hardware at Computex on June 3, 2009, running some DirectX 11 SDK samples. Its features include:
- Tessellation — to increase at runtime the number of visible polygons from a low detail polygonal model
- Multithreaded rendering — to render to the same Direct3D device object from different threads for multi core CPUs
- Compute shaders — which exposes the shader pipeline for non-graphical tasks such as stream processing and physics acceleration, similar in spirit to what OpenCL, Nvidia CUDA, ATI Stream achieves, and HLSL Shader Model 5 among others.
Other notable features are the addition of two new texture compression algorithms for more efficient packing of high quality and HDR/alpha textures and an increased texture cache.
The Direct3D 11 runtime is able to run on Direct3D 9 and 10.x-class hardware and drivers using the concept of "feature levels", expanding on the functionality first introduced in Direct3D 10.1 runtime. Feature levels allow developers to unify the rendering pipeline under Direct3D 11 API and make use of API improvements such as better resource management and multithreading even on entry-level cards, though advanced features such as new shader models and rendering stages will only be exposed on up-level hardware. There are three "10 Level 9" profiles which encapsulate various capabilities of popular DirectX 9.0a cards, and Direct3D 10, 10.1, and 11 each have a separate feature level; each upper level is a strict superset of a lower level.
Tessellation was earlier considered for Direct3D 10, but was later abandoned. GPUs such as Radeon R600 feature a tessellation engine that can be used with Direct3D 9/10/10.1 and OpenGL, but it's not compatible with Direct3D 11 (according to Microsoft). Older graphics hardware such as Radeon 8xxx, GeForce 3/4 had support for another form of tesselation (RT patches, N patches) but those technologies never saw substantial use. As such, their support was dropped from newer hardware.
Microsoft has also hinted at other features such as order independent transparency, which was never exposed by the Direct3D API but supported almost transparently by early Direct3D hardware such as Videologic's PowerVR line of chips.
The Direct3D 11 Technical Preview has been included in November 2008 release of DirectX SDK.
First seen in the Release Candidate version, Windows 7 integrates the first released Direct3D 11 support. The Platform Update for Windows Vista includes full-featured Direct3D 11 runtime and DXGI 1.1 update, as well as other related components from Windows 7 like WARP, Direct2D, DirectWrite, and WIC.
Direct3D 11.1 is an update to the API that ships with Windows 8. The Direct3D runtime in Windows 8 features DXGI 1.2 and requires new WDDM 1.2 device drivers. Preliminary version of the Windows SDK for Windows 8 Developer Preview was released on September 13, 2011.
The new API features shader tracing, support for video playback, shader processing of video resources, and on-the-fly swapping between Direct3D 10 and 11 contexts and feature levels. Direct3D 11.1 includes new feature level 11_1, which brings minor updates to the shader language, such as larger constant buffers and optional double-precision instructions, as well as improved blending modes and mandatory support for 16-bit color formats to improve the performance of entry-level GPUs such as Intel HD Graphics.
The Platform Update for Windows 7 includes a limited set of features from Direct3D 11.1, though components that depend on WDDM 1.2 - such as feature level 11_1 and its related APIs, or quad buffering for stereoscopic rendering - are not present.
Direct3D 11.2 was released in June 2013 with Windows 8.1 Preview. New hardware features require DGXI 1.3 with WDDM 1.3 drivers and include runtime shader modification and linking, low-latency drawing, and optional GPU overlays with frame-buffer scaling for all feature levels. Feature levels 11_0 and 11_1 introduce optional support for mappable default buffers and tiled resources (page-based virtual memory). WARP was updated to fully support feature level 11_1.
Direct3D is a Microsoft DirectX API subsystem component. The aim of Direct3D is to abstract the communication between a graphics application and the graphics hardware drivers. It is presented like a thin abstract layer at a level comparable to GDI (see attached diagram). Direct3D contains numerous features that GDI lacks.
Direct3D is an Immediate mode graphics API. It provides a low-level interface to every video card 3D function (transformations, clipping, lighting, materials, textures, depth buffering and so on). It also had a higher level Retained mode component, that has now been officially discontinued.
Direct3D immediate mode presents three main abstractions: devices, resources and swap chains (see attached diagram). Devices are responsible for rendering the 3D scene. They provide an interface with different rendering capabilities. For example, the mono device provides white and black rendering, while the RGB device renders in color. There are four types of devices:
- HAL (hardware abstraction layer) device: For devices supporting hardware acceleration.
- Reference device: Simulates new functions not yet available in hardware. It is necessary to install the Direct3D SDK to use this device type.
- Null reference device: Does nothing. This device is used when the SDK is not installed and a reference device is requested.
- Pluggable software device: Performs software rendering. This device was introduced with DirectX 9.0.
Moreover, devices contain a collection of resources; specific data used during rendering. Each resource has four attributes:
- Type: Determines the type of resource: surface, volume, texture, cube texture, volume texture, surface texture, index buffer or vertex buffer.
- Pool: Describes how the resource is managed by the runtime and where it is stored. In the Default pool the resource will exist only in device memory. Resources in the managed pool will be stored in system memory, and will be sent to the device when required. Resources in system memory pool will only exist in system memory. Finally, the scratch pool is basically the same as the system memory pool, but resources are not bound by hardware restrictions.
- Format: Describes the layout of the resource data in memory. For example, D3DFMT_R8G8B8 format value means a 24 bits colour depth (8 bits for red, 8 bits for green and 8 bits for blue).
- Usage: Describes, with a collection of flag bits, how the resource will be used by the application. These flags dictate which resources are used in dynamic or static access patterns. Static resource values don’t change after being loaded, whereas dynamic resource values may be modified.
Direct3D implements two display modes:
- Fullscreen mode: The Direct3D application generates all of the graphical output for a display device. In this mode Direct3D automatically captures Alt-Tab and sets/restores screen resolution and pixel format without the programmer intervention. This also provides plenty of problems for debugging due to the 'Exclusive Cooperative Mode'.
- Windowed mode: The result is shown inside the area of a window. Direct3D communicates with GDI to generate the graphical output in the display. Windowed mode can have the same level of performance as full-screen, depending on driver support.
The Microsoft Direct3D 11 API defines a process to convert a group of vertices, textures, buffers, and state into an image on the screen. This process is described as a rendering pipeline with several distinct stages. The different stages of the Direct3D 11 pipeline are:
- Input Assembler: Reads in vertex data from an application supplied vertex buffer and feeds them down the pipeline.
- Vertex Shader: Performs operations on a single vertex at a time, such as transformations, skinning, or lighting.
- Hull Shader: Performs operations on sets of patch control points, and generates additional data known as patch constants.
- Tesselation stage: Subdivides geometry to create higher-order representations of the hull.
- Domain Shader: Performs operations on vertices output by the tessellation stage, in much the same way as a vertex shader.
- Geometry Shader: Processes entire primitives such as triangles, points, or lines. Given a primitive, this stage discards it, or generates one or more new primitives.
- Stream Output: Can write out the previous stage's results to memory. This is useful to recirculate data back into the pipeline.
- Rasterizer: Converts primitives into pixels, feeding these pixels into the pixel shader. The Rasterizer may also perform other tasks such as clipping what is not visible, or interpolating vertex data into per-pixel data.
- Pixel Shader: Determines the final pixel colour to be written to the render target and can also calculate a depth value to be written to the depth buffer.
- Output Merger: Merges various types of output data (pixel shader values, alpha blending, depth/stencil...) to build the final result.
The pipeline stages illustrated with a round box are fully programmable. The application provides a shader program that describes the exact operations to be completed for that stage. Many stages are optional and can be disabled altogether.
Direct3D 10.1 API introduces a concept of "feature levels" which encapsulate features of the hardware supported in a particular version of the API, with separate levels for 10.0 and 10.1 hardware. In previous releases of the Direct3D API, certain capabilities of the graphics hardware have been synonymous with main revision number of the API.
Feature levels allow developers to unify the rendering pipeline and use a single version of the API on both newer and older hardware, taking advantage of performance and usability improvements in the newer runtine. Each upper level is a strict superset of a lower level, with only a few optional features that move to the core functionality on an upper level. More advanced features such as new shader models and rendering stages are only exposed on up-level hardware, however the hardware is not required to support all of these feature levels.
There are seven feature levels provided by
D3D_FEATURE_LEVEL structure; levels 9_1, 9_2 and 9_3 (collectively known as Direct3D 10 Level 9) re-encapsulate various features of popular Direct3D 9 cards conforming to Shader Model 2.0, while levels 10_0, 10_1, 11_0 and 11_1 refer to respective versions of the Direct3D API. "10 Level 9" feature levels contain a subset of the Direct3D 10/11 API and require shaders to be written in HLSL conforming to Shader Model 4.0
4_0_LEVEL_9_x compiler profiles, and not in the actual "shader assembly" language of Shader Model 2.0; SM 3.0 (
ps_3_0) has been omitted deliberately in D3D 10 Level 9.
|Level||Hardware requirements||Supported GPUs|
|9_1||WDDM 1.0 or later. Shader Model 2.0 (
||Intel G965 chipset, Nvidia GeForce FX, Tegra 3 ULP GeForce GPU(Surface RT),Tegra 4 ULP GeForce GPU(Surface 2),|
|9_2||Occlusion queries, floating-point formats (no blending), extended caps, all 9_1 features.||ATI Radeon 9500|
||Nvidia GeForce 6600, ATI Radeon X1300, Adreno 22x/3xx, Matrox M-series, Mali-T 6xx|
|10_0||Shader Model 4.0, geometry shader, stream out, alpha-to-coverage, 8K textures, MSAA textures, 2-sided stencil, general render target views, texture arrays, BC4/BC5, optional DirectCompute (CS 4.0), full floating-point format support, all 9_3 features.||ATI Radeon HD2000 series; Nvidia GeForce 8/9/GTX 200 series, Intel GM965 chipset, Intel HD Graphics (Arrandale/Clarkdale)|
|10_1||Shader Model 4.1, cubemap arrays, extended MSAA, optional DirectCompute (CS 4.1), all 10_0 features.||ATI Radeon HD 3000/4000 series; Nvidia GTX 210/220; Intel HD Graphics 3000/2000 (Sandy Bridge)|
|11_0||WDDM 1.1 or later: Shader Model 5.0, hull & domain shaders, mandatory DirectCompute (CS 5.0), 16K textures, BC6H/BC7, all 10_1 features.
WDDM 1.3 or later: optional mappable buffers, optional tiled resources.
|AMD Radeon HD 5000/6000/7000 series; Nvidia GeForce GTX 400/500/600/700 series; Intel HD Graphics 4000/2500 (Ivy Bridge)|
|11_1||WDDM 1.2 or later. SM5.0 with optional extensions, logical blend operations, target-independent rasterization, UAVs at every stage, constant buffer offsetting and partial updates, UAV only rendering with force sample count, all 11_0 features.
WDDM 1.3 or later: optional mappable buffers, optional tiled resources.
|AMD HD 7000/8000 series, Intel HD Graphics 5000 (Haswell)|
|This section requires expansion. (October 2011)|
Direct3D comes with D3DX, a library of tools designed to perform common mathematical calculations on vectors, matrices and colors, calculating look-at and projection matrices, spline interpolations, and several more complicated tasks, such as compiling or assembling shaders used for 3D graphic programming, compressed skeletal animation storage and matrix stacks. There are several functions that provide complex operations over 3D meshes like tangent-space computation, mesh simplification, precomputed radiance transfer, optimizing for vertex cache friendliness and stripification, and generators for 3D text meshes. 2D features include classes for drawing screen-space lines, text and sprite based particle systems. Spatial functions include various intersection routines, conversion from/to barycentric coordinates and bounding box/sphere generators. D3DX is provided as a dynamic link library (DLL).
Some features present in previous versions of D3DX were removed in Direct3D 11, such as:
- A large part of the math library has been removed. Microsoft recommends use of the XNA Math library instead.
- The Effect framework has been removed and is now distributed as source.
- The Mesh interface has been removed.
DXUT (also called the sample framework) is a layer built on top of the Direct3D API. The framework is designed to help the programmer spend less time with mundane tasks, such as creating a window, creating a device, processing Windows messages and handling device events. It is only usable for writing simple technology-oriented demos, tutorials and workshops.
The Wine project has working implementations of the Direct3D 8, 9 and 10 APIs (they are, as of 23 July 2012, 100%, 78% and 79% complete respectively). Wine's implementation can also be run on Windows under certain conditions. Work on implementing Direct3D 10 began in Wine 1.1.7, using OpenGL via WGL.
Direct3D and Windows Vista
|This article is outdated. (September 2011)|
Windows Vista and its updated driver model brings some new improvements and changes compared to the Windows XP model, and is expected to evolve even more as the hardware and the OS evolve (via future service packs or in the next version of Windows).
Windows Vista forces multithreading, via a theoretically unlimited number of execution contexts on the GPU. Multithreading was already supported in Windows XP as two applications or more could execute in different windows and be hardware accelerated. Windows Vista makes it a requirement to support an arbitrarily large number of execution contexts (or threads) in hardware or in software. Vista, in its basic scheduling incarnation (the current driver model), manages threads all by itself, allowing the hardware to switch from one thread to the other when appropriate. This is a departure from Windows XP, where the hardware could decide to switch threads on its own, as the OS had limited control about what the GPU could do. Also Windows Vista handles memory management and paging (to system memory and to disk), which is a necessity in order to support a large number of execution contexts with their own resources. Each execution context is presented with a resource view of the GPU that matches the maximum available (or exceeds it for aware applications). Most of the management is implemented on the OS side in order to be properly integrated into the OS-kernel memory management.
Execution contexts are protected from each other. Because of the user-mode implementation of the Vista driver, a rogue or badly written app can take control of the execution of the driver and could potentially access data from another process within GPU memory by sending modified commands. Though protected from access by another app, a well-written app still needs to protect itself against failures and device loss caused by other applications. The user-mode implementation can reduce the occurrence of BSODs caused by graphics drivers (which is a much more catastrophic event to a running app than a device-lost event).
Regularly Microsoft spokespeople talked about the necessity to have a finer grain context switching (referred to as "advanced scheduling") so as to be able to switch two execution threads at the shader-instruction level instead of the single-command level or even batch of commands, as in yet-unpublished WDDM 2.x specification. This is not a requirement of Vista, nor of Direct3D 10 compatibility. Direct3D10 apps can run, and are now running, on top of the basic scheduling implementation. This is not typically a problem except for a potential application that would have very long execution of a single command/batch of commands (which is currently prevented under Windows Vista). Vista cannot enforce right now a finer-grained context switching, as it will require additional support from hardware vendors, but it may appear in the future.
Finer-grain preemptive multitasking was introduced in WDDM/DXGI 1.2 which shipped with Windows 8 Developer Preview.
- HLSL – High Level Shader Language
- DirectX – Collection of API's in which Direct3D is implemented
- OpenGL – Main competitor to Direct3D
- 3D computer graphics
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