to a window and vice versa. This allows for techniques such as double buffering. Most of the graphical operations that can be done on windows can also be done on pixmaps. Windows and pixmaps are collectively named drawables, and their content data resides on the server. A client can however request the content of a drawable to be transferred from the server to the client or vice versa. Graphic contexts and fonts The client can request a number of graphic operations, such as clearing an area, copying an area into another, drawing points, lines, rectangles, and text. Beside clearing, all operations are possible on all drawables, both windows and pixmaps. Most requests for graphic operations include a graphic context, which is a structure that contains the parameters of the graphic operations. A graphic context includes the foreground color, the background color, the font of text, and other graphic parameters. When requesting a graphic operation, the client includes a graphic context. Not all parameters of the graphic context affect the operation: for example, the font does not affect drawing a line. The core protocol specifies the use of server-side fonts. Such fonts are stored as files, and the server accesses them either directly via the local filesystem or via the network from another program called font server. Clients can request the list of fonts available to the server and can request a font to be loaded (if not already) or unloaded (if not used by other clients) by the server. A client can request general information about a font (for example, the font ascent) and the space a specific string takes when drawn with a specific font. The names of the fonts are arbitrary strings at the level of the X Window core protocol. The X logical font description conventions specify how fonts should be named according to their attributes. These conventions also specify the values of optional properties that can be attached to fonts. The xlsfonts program prints the list of fonts stored in the server. The xfontsel program shows the glyphs of fonts, and allows the user to select the name of a font for pasting it in another window. The use of server-side fonts is currently considered deprecated in favour of client-side fonts. Such fonts are rendered by the client, not by the server, with the support of the Xft or cairo libraries and the XRender extension. No