X Window System core protocol: Difference between revisions

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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.<ref name="font-faq">{{Cite web|url=http://www.faqs.org/faqs/fonts-faq/part15/|title=comp.fonts FAQ: X11 Info|website=www.faqs.org}}</ref> Such fonts are stored as [[Computer file|file]]s, 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.{{cn|date=March 2025}}

[[Image:Xfontsel.png|thumb|450px|The <code>xfontsel</code> program allows the user to view the glyphs of a font.]]

The names of the fonts are arbitrary strings at the level of the X Window core protocol. The [[X logical font description]] conventions<ref name="logi-font">{{cite web|url=http://www.xfree86.org/current/xlfd.pdf |title=X Logical Font Description Conventions |access-date=2005-12-30 |author=Jim Flowers |author2=Stephen Gildea |year=1994 |format=PDF |work=[[Digital Equipment Corporation]] |publisher=[[X Consortium]] |url-status=dead |archive-url=https://web.archive.org/web/20050328124653/http://www.xfree86.org/current/xlfd.pdf |archive-date=March 28, 2005 }}</ref> 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 <code>xlsfonts</code> program prints the list of fonts stored in the server. The <code>xfontsel</code> program shows the glyphs of fonts, and allows the user to select the name of a font for pasting it in another window.