Because the X server is single-threaded, rendering takes more time by the number of cards. Each card maintains its own copy of all the rendering state, which means that all pixmaps (images) must be copied to every card, too. When any accelerated 2D rendering operation (core, Render, or Xv) is performed, it must be executed on every card. The drawbacks of Xinerama are noticeable. For applications (window managers), there is the Xinerama library, libXinerama for using the Xinerama extension. For instance, a Xinerama-aware window manager can maximize a window to fit one monitor instead of covering all monitors. This allows windows to span more than one monitor, and allow moving windows from monitor to monitor.Īlong with the Xinerama feature came the Xinerama extension, which allows applications to query the physical monitor configuration. The Xinerama desktop feature was developed to combine the graphics cards into a single SCREEN. The above limitation with SCREENs and applications is very inconvenient, when one has several graphics cards to run several monitors. Multiple Graphics Cards, or the story of Xinerama The SCREEN cannot be changed without opening a new connection to the X server, which in practice means you have to quit and restart the application. In other words, the SCREEN where the application windows will appear, must be selected before the application starts (or connects to the X server). Screen number specifies the SCREEN the application has access to. Displaynumber specifies the X server instance, as one computer may have several X servers running. Host specifies the computer, as the X11 protocol can work over a network. The value of DISPLAY is of the form host:displaynumber.screen and the default value set by practically all graphical environments is :0.0, which means the local computer, the X server instance 0, and SCREEN 0. Usually the environment variable DISPLAY specifies which X server to connect to. When a graphical application starts, it connects to an X server. Internally, each SCREEN is driven by a separate driver (DDX) instance, since SCREENs had one-to-one correspondence with graphics cards, too. The only way (that your author knows about) to switch focus from one SCREEN to another is with the mouse. Windows can never span more than one SCREEN, nor can they be moved from one SCREEN to another. They can have, not only different video modes, but also different color depths and resolution (dots-per-inch, used in scaling e.g. The X configuration file ( nf) has one Section "Screen" for each SCREEN, either explicitly written in the file, or nowadays implicitly created by the X server. Dual- or multi-head graphics cards did not really exist, and things were simple. Traditionally in X11, a SCREEN had a one-to-one correspondence with a physical display device (a monitor). The most important concept in understanding how X deals with multiple monitors is the X protocol screen. For actual configuration tutorials, see the links on RandR 1.2 page. You need to know these terms, if you ever need help with a multi-monitor environment. This article explains the basic concepts and terms related to monitors and graphics cards in the X11 world.
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