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diff --git a/xsettings/xsettings.xml b/xsettings/xsettings.xml new file mode 100644 index 0000000..81e901b --- /dev/null +++ b/xsettings/xsettings.xml @@ -0,0 +1,371 @@ +<!doctype article PUBLIC "-//OASIS//DTD DocBook V3.1//EN" [ +]> +<article id="index"> + <artheader> + <title>XSETTINGS - cross toolkit configuration proposal</title> + <releaseinfo>Version 0.5</releaseinfo> + <date>19 March 2001</date> + <authorgroup> + <author> + <firstname>Owen</firstname> + <surname>Taylor</surname> + <affiliation> + <address> + <email>otaylor@redhat.com</email> + </address> + </affiliation> + </author> + </authorgroup> + </artheader> + + <sect1 id="goals"> + <title>Goals</title> + <para> + The intent of this specification is to specify a mechanism to + allow the configuration of settings such as double click timeout, + drag-and-drop threshold, and default foreground and background colors + for all applications running within a desktop. The mechanism should: + </para> + <simplelist> + <member>allow for instant updates to be propagated across all + applications at runtime</member> + <member>perform well, even for remote applications.</member> + </simplelist> + <para> + It is not intended: + </para> + <simplelist> + <member>for the storage of application-specific data</member> + <member>to be able to store large amounts of data</member> + <member>to store complex data types (other than as + strings)</member> + </simplelist> + </sect1> + <sect1 id="existing"> + <title>Existing Systems</title> + <para> + The existing systems in this area are the Xrm database, and various + other configuration database systems, mostly specific to particular + desktops. (The kde configuration system, gnome-config, GConf, + libproplist, etc.) + </para> + <para> + The Xrm database is tempting to use for this purpose since it is + very well established and has a universally deployed existing + implementation. However, it has various defects, that make it + not suitable for this purpose. + </para> + <itemizedlist> + <listitem> + <para> + The Xrm database merges information from various sources - the + ~/.Xdefaults file on the root window, and a property on the root + window. This means that to programatically configure the Xrm + database in response to a GUI config tool is difficult and + unreliable. + </para> + </listitem> + <listitem> + <para> + The Xrm database was not designed for on-the-fly changing of + settings. + </para> + </listitem> + <listitem> + <para> + The Xrm database stores all information in a single text + property on the root window. This makes it difficult to + determine what settings have changed; it is necessary to parse + the property and do string comparisons. + </para> + <para> + Additionally, most systems have a large amount of application + specific information in the Xrm database, which further slows + down notification of changes. + </para> + </listitem> + </itemizedlist> + <para> + Other configuration databases are more designed for this + task. However, they are sophisticated systems that are not easily + reimplementable. Also, picking one would mean difficulties + integrating with other desktops that use different systems. + </para> + <para> + It is our contention that a system designed specifically for + configuration of a small number of settings being changed at + runtime can, compared to a more general existing system: + </para> + <simplelist> + <member>Be easier to bridge onto each systems native configuration + mechanism.</member> + <member>Be easier to implement in whatever language/library combination + people want to use.</member> + <member>Be more efficient.</member> + </simplelist> + </sect1> + <sect1 id="client-behavior"> + <title>Client behavior</title> + <para> + On startup, each client that should identify the settings window by + calling XGetSelectionOwner() for the _XSETTINGS_S[N] selection and select + for notification on the settings window by calling XSelectInput() + with a mask of StructureNotifyMask|PropertyChangeMask. + </para> + <para> + To prevent race conditions a client MUST grab the + server while performing these operations using XGrabServer(). + </para> + <para> + If there is no owner of the _XSETTINGS_S[N] selection, the client can + determine when an owner is established by listening for client + messages sent to root window of the screen with type MANAGER. (See + section 2.8, Manager Selections of the ICCCM.) The format of this + message is: + </para> + <programlisting> + event-mask: StructureNotify + event: ClientMessage + type: MANAGER + format: 32 + data[0]: timestamp + data[1]: _XSETTINGS_S[N] (atom) + data[2]: New owner of the selection + data[3]: 0 (reserved) + </programlisting> + <para> + The client can then proceed to read contents of the _XSETTINGS_SETTINGS + property from the settings window and interpret according to + the information in the "_XSETTINGS_SETTINGS Format" section of this + document. + </para> + <para> + Clients must trap X errors when reading the _XSETTING_SETTINGS property + because it is possible that the selection window may be destroyed + at any time. + </para> + <para> + When the client is notified that the settings window has been + destroyed or discovers that the selection window has been destroyed, + it should reset all settings to their default values and then proceed + as on initial startup. [ See rational section ] + </para> + <para> + When a client receives a PropertyChangeNotify event for the window + it should reread the _XSETTING_SETTINGS property. It can use + the 'serial' field to tell what fields have been changed. The + client must parse the entire property and read in all new values + before taking action on changed settings such as notifying listeners + for those settings to avoid using a mix of old and new data. + </para> + </sect1> + <sect1 id="format"> + <title>_XSETTINGS_SETTINGS Format</title> + <para> + The _XSETTINGS_SETTINGS property is of form 8 and type _XSETTINGS_SETTINGS. +The contents are a + </para> + <programlisting> + 1 CARD8 byte-order + 3 unused + 4 CARD32 SERIAL + 4 CARD32 N_SETTINGS + </programlisting> + <para> +Followed by N_SETTINGS settings records, which have a header: + </para> + <programlisting> + 1 SETTING_TYPE type + 1 unused + 2 n name-len + n STRING8 name + P unused, p=pad(n) + 4 CARD32 last-change-serial + </programlisting> + <para> +Where SETTING_TYPE is + </para> + <programlisting> + 0 XSettingsTypeInteger + 1 XSettingsTypeString + 2 XSettingsTypeColor + </programlisting> + <para> +followed by the body. If TYPE = XSettingsTypeString the body is: + </para> + <programlisting> + 4 n value-len + n STRING8 value + P unused, p=pad(n) + </programlisting> + + <para> +If TYPE == XSettingsTypeInteger, then the body is: + </para> + <programlisting> + 4 INT32 value + </programlisting> + + <para> + If TYPE == XSettingsTypeColor, then the body is: + </para> + <programlisting> + 2 CARD16 red + 2 CARD16 blue + 2 CARD16 green + 2 CARD16 alpha + </programlisting> + <para> +If the setting does not need the alpha field, it should +be set to 65535. + </para> + <para> + Setting names must be confined to the ascii characters: + </para> + <programlisting> + 'A'-'Z' 'a'-'z' '0'-'9' '_' and '/' + </programlisting> + <para> + With the additional restrictions that '/' cannot appear in + the leading or trailing position, that two occurences of + '/' cannot be consecutive, and that the first character + of the name, and and the first character after a slash + cannot be one of '0'-'9'. Names may not be empty. + </para> + <para> + So, + </para> + <programlisting> + "GTK/colors/background0" + "_background" + "_111" + </programlisting> + <para> + are legitimate names, while + </para> + <programlisting> + "/" + "_background/" + "GTK//colors" + "" + </programlisting> + <para> + Are not legitimate names. + </para> + <para> + The names, types, contents, and default values of standard settings + will be separately agreed upon. + </para> + + <para> + Names beginning with 'Net/' and case variants of that string are + reserved and must not be used without prior agreement. + </para> + <para> + The 'serial' field and and the 'last-change-serial' field of the each + settings record can be used to tell which settings have changed since + the last time a client retrieved the _XSETTINGS_SETTINGS property. Each + time the client retrieves the contents of the _XSETTINGS_SETTINGS + property it should store the contents of the 'serial' field. When + it next retrieves the property, any settings whose 'last-change-serial' + is greater than the stored value. + </para> + + <para> + (Careful clients will make provisions for wrap-around of the serial + field. This is, however, not expected to happen in practice.) + </para> + </sect1> + <sect1 id="manager-behavior"> + <title>Settings Manager behavior</title> + <para> + The _XSETTING_S[N] selection is managed as a manager selection + according to section 2.8 of the ICCCM and the handling of the + selections window, the _XSETTING_S[N] window and MANAGER client + messages must conform to that specification. + </para> + <para> + The settings manager changes the contents of the _XSETTINGS_SETTINGS + property of the root window whenever the source it derives them + from changes, taking care to increment the 'serial' field at each + increment and set the 'last-change-serial' fields appropriately. + </para> + </sect1> + <appendix id="rational"> + <title>Rational and Discussion</title> + <para> + The reasons why an existing configuration mechanism, and in particular, + the Xrm database, was not used is discussed above. Various other + design decisions are discussed below: + </para> + <formalpara> + <title>Why aren't the contents of the property stored in XML?</title> + <para> + The data format is designed to be space efficient and to be easily + and efficiently parsed with minimal code. These are not things + XML does well. Flexibility of structure, things that XML + does well are not needed here. If needed, XML can be used for + the contents of individual settings. + </para> + </formalpara> + <formalpara> + <title>Why is the settings property screen specific?</title> + <para> + While most settings are expected to be shared across all screens + of a display, some settings, such as font sizes will be screen + specific, and it is considered easier to let the settings manager + propagate shared resources across screens then to have both + screen-specific and screen-independent resources. + </para> + </formalpara> + <formalpara> + <title>Why does there need to be a "settings manager" process + running?</title> + <para> + Having a process always present as the owner of the _XSETTING + selection ensures that there are no race conditions and is + simpler than trying to create a locking mechanism that can + work without a persistant process. It is also expected that to + properly handle notification of changes to the stored + properties most desktops will want a process running to watch + for changes in any case. In cases of tight resource usage, the + settings manager can be combined with some other function, + such as the window manager or session manager. + </para> + </formalpara> + <formalpara> + <title>Why use a single property for all settings?</title> + <para> + Using a single property has several advantages. First, retrieving + all settings takes only a single round-trip to the server instead + of a round-trip for each settings. Second, it means that when + multiple settings can be changed at once, only a single notification + is received by clients, and clients will see interrelated properties + changed in an atomic fashion. + </para> + </formalpara> + <formalpara> + <title>Why is the _XSETTINGS_SETTINGS property stored in the endianess + of the manager instead of a neutral endianness?</title> + <para> + This conforms to the way many other X mechanisms work. The main reason + for doing it this way is to save conversions for the common case when + the client and manager are on machines of the same endianness. + </para> + </formalpara> + <formalpara> + <title>When the settings manager exits, why should clients reset the + values to the default settings instead of keeping the current + settings?</title> + <para> + Resetting the settings to the default values is preferred to + maintaining the current values because it makes sure that all programs + on the desktop have consistent values for settings whether they were + started before or after the settings manager exited. It is not + expected that changes in the current settings manager will occur + very often. + </para> + </formalpara> + </appendix> +</article> + |