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Direct3D is a graphics application programming interface (API) for Microsoft Windows. Direct3D is used to render three-dimensional graphics in applications where performance is important, such as games. 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, W-buffering, Stencil buffering , spatial anti-aliasing, alpha blending, colour blending, mipmapping, texture blending,clipping, Culling, atmospheric effects, perspective-correct texture mapping, programmable HLSL shaders and effects. 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 Direct3D contains many commands for 3D computer graphics rendering; however, since version 8, Direct3D has superseded the DirectDraw framework and also taken responsibility for the rendering of 2D graphics.〔(【引用サイトリンク】title=DirectX Software Development Kit, October 2006 )〕 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.〔(【引用サイトリンク】title=Windows Advanced Rasterization Platform (WARP) Guide - WARP Architecture and Performance )〕 Part of DirectX, Direct3D is available for Windows 95 and above, and is the base for the vector graphics API on the Xbox and Xbox 360 console systems. The Wine compatibility layer, a free software reimplementation of several Windows APIs, includes an implementation of Direct3D. Direct3D's main competitor is OpenGL. Fahrenheit was an attempt by Microsoft and SGI to unify OpenGL and Direct3D in the 1990s, but was eventually cancelled. ==DirectX 2.0 and 3.0== 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. The first version of Direct3D shipped in DirectX 2.0 (June 2, 1996) and DirectX 3.0 (September 26, 1996). Direct3D initially implemented "retained mode" and "immediate mode" 3D APIs. Like other DirectX APIs, such as DirectDraw, both were based on COM. The retained mode was a 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. For DirectX 2.0 and 3.0, the Direct3D immediate mode used 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 to perform the 3D rendering. They were extremely awkward to program, however, hindering adoption of the new API and prompting 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. From the beginning, the immediate mode also supported Talisman's tiled rendering with the BeginScene/EndScene methods of the IDirect3DDevice interface. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Direct3D」の詳細全文を読む スポンサード リンク
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