Editing Direct Rendering Infrastructure (section)

== Software architecture ==
The basic architecture of the Direct Rendering Infrastructure involves three main components:<ref name="Martin et all 1999 DRI low level">{{cite web|last1=Martin|first1=Kevin E.|last2=Faith|first2=Rickard E.|last3=Owen|first3=Jens|last4=Akin|first4=Allen|title=Direct Rendering Infrastructure, Low-Level Design Document|url=http://dri.sourceforge.net/doc/design_low_level.html|access-date=18 May 2016|date=11 May 1999|archive-date=23 July 2016|archive-url=https://web.archive.org/web/20160723091323/http://dri.sourceforge.net/doc/design_low_level.html|url-status=dead}}</ref>
* the DRI client &mdash;for example, an X client performing "direct rendering"&mdash; needs a hardware-specific "driver" able to manage the current video card or graphics adapter in order to render on it. These ''DRI drivers'' are typically provided as [[shared libraries]] to which the client is [[Dynamic linker|dynamically linked]]. Since DRI was conceived to take advantage of 3D graphics hardware, the libraries are normally presented to clients as hardware-accelerated implementations of a 3D API such as [[OpenGL]], provided by either the 3D-hardware vendor itself or a third party such as the [[Mesa 3D]] [[free software]] project.
* the X Server provides an [[X Window System core protocol|X11 protocol extension]] &mdash;the DRI extension&mdash; that the DRI clients use to coordinate with both the [[windowing system]] and the DDX driver.<ref name="DRI extension">{{cite web|last1=Owen|first1=Jens|last2=Martin|first2=Kevin|title=DRI Extension for supporting Direct Rendering - Protocol Specification|url=http://dri.sourceforge.net/doc/dri_extensions_low_level.txt|access-date=18 May 2016|date=11 May 1999}}</ref> As part of the DDX driver, it's quite common that the X Server process also dynamically links to the same DRI driver that the DRI clients do, but to provide hardware-accelerated 3D rendering to the X clients using the [[GLX]] extension for indirect rendering (for example, remote X clients that can't use direct rendering). For 2D rendering, the DDX driver must also take into account the DRI clients using the same graphics device.
* the access to the video card or graphics adapter is regulated by a kernel component called the [[Direct Rendering Manager]] (DRM).<ref name="Faith 1999">{{cite web|last1=Faith|first1=Rickard E.|title=The Direct Rendering Manager: Kernel Support for the Direct Rendering Infrastructure|url=https://dri.sourceforge.net/doc/drm_low_level.html|date=11 May 1999|access-date=18 May 2016|archive-date=21 May 2024|archive-url=https://web.archive.org/web/20240521055530/https://dri.sourceforge.net/doc/drm_low_level.html|url-status=dead}}</ref> Both the X Server's DDX driver and each X client's DRI driver must use DRM to access the graphics hardware. DRM provides [[Synchronization (computer science)|synchronization]] to the shared resources of the graphics hardware &mdash;resources such as the command queue, the card registers, the video memory, the DMA engines, ...&mdash; ensuring that the concurrent access of all those multiple competing user-space processes don't interfere with each other. DRM also serves as a basic security enforcer that doesn't allow any X client to access the hardware beyond what it needs to perform the 3D rendering.