Direct Graphics Access is a plug-in for the X

display server In computing, a windowing system (or window system) is software that manages separately different parts of display screens. It is a type of graphical user interface (GUI) which implements the WIMP (windows, icons, menus, pointer) paradigm for ...

s that allows client programs direct access to the

frame buffer A framebuffer (frame buffer, or sometimes framestore) is a portion of random-access memory (RAM) containing a bitmap that drives a video display. It is a memory buffer containing data representing all the pixels in a complete video frame. Modern ...

Graphics hardware Graphics hardware is computer hardware that generates computer graphics and allows them to be shown on a display, usually using a graphics card (video card) in combination with a device driver to create the images on the screen. Types Gra ...

communicates via a chunk of

memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...

called a frame buffer. This is an array of values that represent

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the smal ...

color values on the

screen Screen or Screens may refer to: Arts * Screen printing (also called ''silkscreening''), a method of printing * Big screen, a nickname associated with the motion picture industry * Split screen (filmmaking), a film composition paradigm in which mul ...

. Writing the appropriate values into the frame buffer therefore allows a program to ''paint'' areas of the screen. However, as with any

shared resource In computing, a shared resource, or network share, is a System resource, computer resource made available from one Host (network), host to other hosts on a computer network. It is a device or piece of information on a computer that can be remot ...

, problems occur when multiple programs attempt to access the same resource, as they tend to write over each other's work. In the

X Window System The X Window System (X11, or simply X) is a windowing system for bitmap displays, common on Unix-like operating systems. X provides the basic framework for a GUI environment: drawing and moving windows on the display device and interacting wit ...

, this is solved by having a central

that mediates between programs that want to draw on the screen. The display server also used to perform a lot of the drawing work, allowing programs to say ''Draw me a circle of this radius filled with this pattern'' or ''draw this text in this font''. The X server does all this work, freeing programmers from having to write their own drawing code. Another advantage of the X architecture is that it works over a

network Network, networking and networked may refer to: Science and technology * Network theory, the study of graphs as a representation of relations between discrete objects * Network science, an academic field that studies complex networks Mathematics ...

, allowing programs on one machine to display output on the screen of another. Direct Graphics Access allows direct access to the frame buffer and the X-server hands over control of the frame buffer to the client program and waits for the client to hand it back. This means that the client program has control of the whole screen, and so it is mostly used for full-screen video/games.

External links

XFree86 server 4.x Design (DRAFT) : DGA Extension

XDGA man page
{{XWinSys Image processing X Window extensions

See also

External links