X11 Screen Saver Extension

MIT X Consortium Proposed Standard

Jim Fulton

   Network Computing Devices, Inc

Keith Packard

   X Consortium, Laboratory for Computer Science, Massachusetts
   Institute of Technology

   X Version 11, Release 7.7

   Version 1.0

   Copyright © 1992 Massachusetts Institute of Technology, Network
   Computing Devices, Inc

   Permission to use, copy, modify, and distribute this
   documentation for any purpose and without fee is hereby
   granted, provided that the above copyright notice and this
   permission notice appear in all copies. MIT and Network
   Computing Devices, Inc. make no representations about the
   suitability for any purpose of the information in this
   document. This documentation is provided "as is" without
   express or implied warranty.
     __________________________________________________________

   Table of Contents

   1. Introduction
   2. Assumptions
   3. Overview
   4. Issues
   5. Protocol

        Types
        Errors
        Requests
        Events

   6. Encoding

        Common Types
        Requests
        Events

   7. Inter-Client Communications Conventions
   8. C language binding

Chapter 1. Introduction

   The X Window System provides support for changing the image on
   a display screen after a user-settable period of inactivity to
   avoid burning the cathode ray tube phosphors. However, no
   interfaces are provided for the user to control the image that
   is drawn. This extension allows an external "screen saver"
   client to detect when the alternate image is to be displayed
   and to provide the graphics.

   Current X server implementations typically provide at least one
   form of "screen saver" image. Historically, this has been a
   copy of the X logo drawn against the root background pattern.
   However, many users have asked for the mechanism to allow them
   to write screen saver programs that provide capabilities
   similar to those provided by other window systems. In
   particular, such users often wish to be able to display
   corporate logos, instructions on how to reactivate the screen,
   and automatic screen-locking utilities. This extension provides
   a means for writing such clients.

Chapter 2. Assumptions

   This extension exports the notion of a special screen saver
   window that is mapped above all other windows on a display.
   This window has the override-redirect attribute set so that it
   is not subject to manipulation by the window manager.
   Furthermore, the X identifier for the window is never returned
   by QueryTree requests on the root window, so it is typically
   not visible to other clients.

Chapter 3. Overview

   The core SetScreenSaver request can be used to set the length
   of time without activity on any input devices after which the
   screen saver should "activate" and alter the image on the
   screen. This image periodically "cycles" to reduce the length
   of time that any particular pixel is illuminated. Finally, the
   screen saver is "deactivated" in response to activity on any of
   the input devices or particular X requests.

   Screen saving is typically done by disabling video output to
   the display tube or by drawing a changing pattern onto the
   display. If the server chooses the latter approach, a window
   with a special identifier is created and mapped at the top of
   the stacking order where it remains until the screen saver
   deactivates. At this time, the window is unmapped and is not
   accessible to any client requests.

   The server's default mechanism is referred to as the internal
   screen saver. An external screen saver client requires a means
   of determining the window id for the screen saver window and
   setting the attributes (e.g. size, location, visual, colormap)
   to be used when the window is mapped. These requirements form
   the basis of this extension.

Chapter 4. Issues

   This extension raises several interesting issues. First is the
   question of what should be done if some other client has the
   server grabbed when the screen saver is supposed to activate?
   This commonly occurs with window managers that automatically
   ask the user to position a window when it is first mapped by
   grabbing the server and drawing XORed lines on the root window.

   Second, a screen saver program must control the actual RGB
   values sent to the display tube to ensure that the values
   change periodically to avoid phosphor burn in. Thus, the client
   must have a known colormap installed whenever the screen saver
   window is displayed. To prevent screen flashing, the visual
   type of the screen saver window should also be controllable.

   Third, some implementations may wish to destroy the screen
   saver window when it is not mapped so that it need not be
   avoided during event delivery. Thus, screen saver clients may
   find that the requests that reference the screen saver window
   may fail when the window is not displayed.

Chapter 5. Protocol

   Table of Contents

   Types
   Errors
   Requests
   Events

   The Screen Saver extension is as follows:

Types

   In addition to the common types described in the core protocol,
   the following type is used in the request and event definitions
   in subsequent sections.
   Name             Value
   SCREENSAVEREVENT ScreenSaverNotify, ScreenSaverCycle

Errors

   The Screen Saver extension adds no errors beyond the core
   protocol.

Requests

   The Screen Saver extension adds the following requests:

   ScreenSaverQueryVersion
        client-major-version: CARD8
        client-minor-version: CARD8
   ->
        server-major-version: CARD8
        server-minor-version: CARD8

   This request allows the client and server to determine which
   version of the protocol should be used. The client sends the
   version that it prefers; if the server understands that
   version, it returns the same values and interprets subsequent
   requests for this extension according to the specified version.
   Otherwise, the server returns the closest version of the
   protocol that it can support and interprets subsequent requests
   according to that version. This document describes major
   version 1, minor version 0; the major and minor revision
   numbers should only be incremented in response to incompatible
   and compatible changes, respectively.

   ScreenSaverQueryInfo
   drawable DRAWABLE
   saver-window: WINDOW
   state: {Disabled, Off, On}
   kind: {Blanked, Internal, External}
   til-or-since: CARD32
   idle: CARD32
   event-mask: SETofSCREENSAVEREVENT
   Errors: Drawable

   This request returns information about the state of the screen
   saver on the screen associated with drawable. The saver-window
   is the XID that is associated with the screen saver window.
   This window is not guaranteed to exist except when external
   screen saver is active. Although it is a child of the root,
   this window is not returned by QueryTree requests on the root.
   Whenever this window is mapped, it is always above any of its
   siblings in the stacking order. XXX - TranslateCoords?

   The state field specifies whether or not the screen saver is
   currently active and how the til-or-since value should be
   interpreted:
   Off The screen is not currently being saved; til-or-since
   specifies the number of milliseconds until the screen saver is
   expected to activate.
   On The screen is currently being saved; til-or-since specifies
   the number of milliseconds since the screen saver activated.
   Disabled The screen saver is currently disabled; til-or-since
   is zero.

   The kind field specifies the mechanism that either is currently
   being used or would have been were the screen being saved:
   Blanked The video signal to the display monitor was disabled.
   Internal A server-dependent, built-in screen saver image was
   displayed; either no client had set the screen saver window
   attributes or a different client had the server grabbed when
   the screen saver activated.
   External The screen saver window was mapped with attributes set
   by a client using the ScreenSaverSetAttributes request.

   The idle field specifies the number of milliseconds since the
   last input was received from the user on any of the input
   devices.

   The event-mask field specifies which, if any, screen saver
   events this client has requested using ScreenSaverSelectInput.

   If drawable is not a valid drawable identifier, a Drawable
   error is returned and the request is ignored.

   ScreenSaverSelectInput
   drawable: DRAWABLE
   event-mask: SETofSCREENSAVEREVENT

   Errors: Drawable, Match

   This request specifies which Screen Saver extension events on
   the screen associated with drawable should be generated for
   this client. If no bits are set in event-mask, then no events
   will be generated. Otherwise, any combination of the following
   bits may be set:
   ScreenSaverNotify If this bit is set, ScreenSaverNotify events
   are generated whenever the screen saver is activated or
   deactivated.
   ScreenSaverCycle If this bit is set, ScreenSaverNotify events
   are generated whenever the screen saver cycle interval passes.

   If drawable is not a valid drawable identifier, a Drawable
   error is returned. If any undefined bits are set in event-mask,
   a Value error is returned. If an error is returned, the request
   is ignored.

   ScreenSaverSetAttributes

   drawable: DRAWABLE
   class:
   {InputOutput, InputOnly, CopyFromParent}
   depth: CARD8
   visual: VISUALID or CopyFromParent
   x, y: INT16
   width, height, border-width: CARD16
   value-mask: BITMASK
   value-list: LISTofVALUE
   Access, Window, Pixmap, Colormap, Cursor, Match, Value, Alloc

   This request sets the attributes that this client would like to
   see used in creating the screen saver window on the screen
   associated with drawable. If another client currently has the
   attributes set, an Access error is generated and the request is
   ignored.

   Otherwise, the specified window attributes are checked as if
   they were used in a core CreateWindow request whose parent is
   the root. The override-redirect field is ignored as it is
   implicitly set to True. If the window attributes result in an
   error according to the rules for CreateWindow, the request is
   ignored.

   Otherwise, the attributes are stored and will take effect on
   the next activation that occurs when the server is not grabbed
   by another client. Any resources specified for the
   background-pixmap or cursor attributes may be freed
   immediately. The server is free to copy the background-pixmap
   or cursor resources or to use them in place; therefore, the
   effect of changing the contents of those resources is
   undefined. If the specified colormap no longer exists when the
   screen saver activates, the parent's colormap is used instead.
   If no errors are generated by this request, any previous screen
   saver window attributes set by this client are released.

   When the screen saver next activates and the server is not
   grabbed by another client, the screen saver window is created,
   if necessary, and set to the specified attributes and events
   are generated as usual. The colormap associated with the screen
   saver window is installed. Finally, the screen saver window is
   mapped.

   The window remains mapped and at the top of the stacking order
   until the screen saver is deactivated in response to activity
   on any of the user input devices, a ForceScreenSaver request
   with a value of Reset, or any request that would cause the
   window to be unmapped.

   If the screen saver activates while the server is grabbed by
   another client, the internal saver mechanism is used. The
   ForceScreenSaver request may be used with a value of Active to
   deactivate the internal saver and activate the external saver.

   If the screen saver client's connection to the server is broken
   while the screen saver is activated and the client's close down
   mode has not been RetainPermanent or RetainTemporary, the
   current screen saver is deactivated and the internal screen
   saver is immediately activated.

   When the screen saver deactivates, the screen saver window's
   colormap is uninstalled and the window is unmapped (except as
   described below). The screen saver XID is disassociated with
   the window and the server may, but is not required to, destroy
   the window along with any children.

   When the screen saver is being deactivated and then immediately
   reactivated (such as when switching screen savers), the server
   may leave the screen saver window mapped (typically to avoid
   generating exposures).

   ScreenSaverUnsetAttributes

   drawble: DRAWABLE
   Errors: Drawable

   This request notifies the server that this client no longer
   wishes to control the screen saver window. Any screen saver
   attributes set by this client and any descendents of the screen
   saver window created by this client should be released
   immediately if the screen saver is not active, else upon
   deactivation.

   This request is ignored if the client has not previously set
   the screen saver window attributes.

Events

   The Screen Saver extension adds one event:

   ScreenSaverNotify

   root: WINDOW
   window: WINDOW
   state: {Off, On, Cycle}
   kind: { Blanked, Internal , External }
   forced: BOOL
   time: TIMESTAMP

   This event is delivered to clients that have requested
   ScreenSaverNotify events using the ScreenSaverSelectInput
   request whenever the screen saver activates or deactivates.

   The root field specifies root window of the screen for which
   the event was generated. The window field specifies the value
   that is returned by ScreenSaverQueryInfo as the identifier for
   the screen saver window. This window is not required to exist
   if the external screen saver is not active.

   The state field specifies the cause of the event:
   Off The screen saver deactivated; this event is sent if the
   client has set the ScreenSaverNotify bit in its event mask.
   On The screen saver activated. This event is sent if the client
   has set the ScreenSaverNotify bit in its event mask.
   Cycle The cycle interval passed and the client is expected to
   change the image on the screen. This event is sent if the
   client has set the ScreenSaverCycle bit in its event mask.

   If state is set to On or Off then forced indicates whether or
   not activation or deactivation was caused by a core
   ForceScreenSaver request; otherwise, forced is set to False.

   The kind field specifies mechanism that was used to save the
   screen when the screen saver was activated, as described in
   ScreenSaverQueryInfo.

   The time field indicates the server time when the event was
   generated.

Chapter 6. Encoding

   Table of Contents

   Common Types
   Requests
   Events

   Please refer to the X11 Protocol Encoding document as this
   document uses conventions established there.

   The name of this extension is "SCREEN-SAVER".

Common Types

SETofSCREENSAVEREVENT
     #x00000001     ScreenSaverNotifyMask
     #x00000002     ScreenSaverCycleMask

Requests

ScreenSaverQueryVersion
1     CARD8                   screen saver opcode
1     0                       minor opcode
2     2                       request length
1     CARD8                   client major version
1     CARD8                   client minor version
2                             unused
->
1     1                       Reply
1                             unused
2     CARD16                  sequence number
4     0                       reply length
1     CARD8                   server major version
1     CARD8                   server minor version
22                            unused

ScreenSaverQueryInfo
1     CARD8                   screen saver opcode
1     1                       minor opcode
2     2                       request length
4     DRAWABLE                drawable associated with screen
->
1     1                       Reply
1     CARD8                   state
      0          Off
      1          On
      3          Disabled
2     CARD16                  sequence number
4     0                       reply length
4     WINDOW                  saver window
4     CARD32                  milliseconds until saver or since saver
4     CARD32                  milliseconds since last user device input
4     SETofSCREENSAVEREVENT   event mask
1     CARD8                   kind
      0          Blanked
      1          Internal
      2          External
10               unused

ScreenSaverSelectInput
1     CARD8                   screen saver opcode
1     2                       minor opcode
2     3                       request length
4     DRAWABLE                drawable associated with screen
4     SETofSCREENSAVEREVENT   event mask

ScreenSaverSetAttributes
1     CARD8                   screen saver opcode
1     3                       minor opcode
2     6+n                     request length
4     DRAWABLE                drawable associated with screen
2     INT16                   x
2     INT16                   y
2     CARD16                  width
2     CARD16                  height
2     CARD16                  border-width
1                             class
      0          CopyFromParent
      1          InputOutput
      2          InputOnly
1     CARD8                   depth
4     VISUALID                visual
      0          CopyFromParent
4     BITMASK                 value-mask (has n bits set to 1)
      encodings are the same as for core CreateWindow
4n    LISTofVALUE             value-list
      encodings are the same as for core CreateWindow

ScreenSaverUnsetAttributes
1     CARD8                   screen saver opcode
1     4                       minor opcode
2     3                       request length
4     DRAWABLE                drawable associated with screen

Events

ScreenSaverNotify
1     CARD8                   code assigned by core
1     CARD8                   state
      0          Off
      1          On
      2          Cycle
2     CARD16                  sequence number
4     TIMESTAMP               time
4     WINDOW                  root
4     WINDOW                  screen saver window
1     CARD8                   kind
      0          Blanked
      1          Internal
      2          External
1     BOOL                    forced
14                            unused

Chapter 7. Inter-Client Communications Conventions

   Screen saver clients should create at least one resource value
   whose identifier can be stored in a property named
   _SCREEN_SAVER_ID on the root of each screen it is managing.
   This property should have one 32-bit value corresponding to the
   resource identifier; the type of the property should indicate
   the type of the resource and should be one of the following:
   WINDOW, PIXMAP, CURSOR, FONT, or COLORMAP.

Chapter 8. C language binding

   The C binding for this extension simply provide access to the
   protocol; they add no semantics beyond what is described above.

   The include file for this extension is
   <X11/extensions/scrnsaver.h>.

   Bool XScreenSaverQueryExtension(Display *display, int
   *event_base, int *error_base);

   This routine returns True if the specified display supports the
   SCREEN-SAVER extension; otherwise it returns False. If the
   extension is supported, the event number for ScreenSaverNotify
   events is returned in the value pointed to by event_base. Since
   no additional errors are defined by this extension, the results
   of error_base are not defined.

   Status XScreenSaverQueryVersion(Display *display, int *major,
   int *minor);

   If the specified display supports the extension, the version
   numbers of the protocol expected by the server are returned in
   major and minor and a non-zero value is returned. Otherwise,
   the arguments are not set and 0 is returned.

   XScreenSaverInfo *

   XScreenSaverAllocInfo()

   This routine allocates and returns an XScreenSaverInfo
   structure for use in calls to XScreenSaverQueryInfo. All fields
   in the structure are initialized to zero. If insufficient
   memory is available, NULL is returned. The results of this
   routine can be released using XFree.

   Status XScreenSaverQueryInfo(Display *display, Drawable
   drawable, XScreenSaverInfo *saver_info);

   If the specified display supports the extension, information
   about the current state of the screen server is returned in
   saver_info and a non-zero value is returned. The
   XScreenSaverInfo structure is defined as follows:
typedef struct {
    Window window;                /* screen saver window */
    int state;                    /* ScreenSaver{Off,On,Disabled} */
    int kind;                     /* ScreenSaver{Blanked,Internal,Extern
al} */
    unsigned long til_or_since;   /* milliseconds */
    unsigned long idle;           /* milliseconds */
    unsigned long event_mask;     /* events */
} XScreenSaverInfo;

   See the ScreenSaverQueryInfo request for a description of the
   fields. If the extension is not supported, saver_info is not
   changed and 0 is returned.

   void XScreenSaverSelectInput(Display *display, Drawable
   drawable, unsigned long event_mask);

   If the specified display supports the extension, this routine
   asks that events related to the screen saver be generated for
   this client. The format of the events generated is:
typedef struct {
    int type;               /* of event */
    unsigned long serial;   /* # of last request processed by server */
    Bool send_event;        /* true if this came from a SendEvent reques
t */
    Display *display;       /* Display the event was read from */
    Window window;          /* screen saver window */
    Window root;            /* root window of event screen */
    int state;              /* ScreenSaver{Off,On,Cycle} */
    int kind;               /* ScreenSaver{Blanked,Internal,External} */
    Bool forced;            /* extents of new region */
    Time time;              /* event timestamp */
} XScreenSaverNotifyEvent;

   See the definition of the ScreenSaverSelectInput request for
   descriptions of the allowed event masks.

   void XScreenSaverSetAttributes(Display *dpy, Drawable drawable,
   int x, int y, unsigned int width, unsigned int height, unsigned
   int border_width, int depth, unsigned int class, Visual
   *visual, unsigned long valuemask, XSetWindowAttributes
   *attributes);

   If the specified display supports the extension, this routine
   sets the attributes to be used the next time the external
   screen saver is activated. See the definition of the
   ScreenSaverSetAttributes request for a description of each of
   the arguments.

   void XScreenSaverUnsetAttributes(Display *display, Drawable
   drawable);

   If the specified display supports the extension, this routine
   instructs the server to discard any previous screen saver
   window attributes set by this client.

   Status XScreenSaverRegister(Display *display, int screen, XID
   xid, Atom type);

   This routine stores the given XID in the _SCREEN_SAVER_ID
   property (of the given type) on the root window of the
   specified screen. It returns zero if an error is encountered
   and the property is not changed, otherwise it returns non-zero.

   Status XScreenSaverUnregister(Display *display, int screen);

   This routine removes any _SCREEN_SAVER_ID from the root window
   of the specified screen. It returns zero if an error is
   encountered and the property is changed, otherwise it returns
   non-zero.

   Status XScreenSaverGetRegistered(Display *display, int screen,
   XID *xid, ATOM *type);

   This routine returns the XID and type stored in the
   _SCREEN_SAVER_ID property on the root window of the specified
   screen. It returns zero if an error is encountered or if the
   property does not exist or is not of the correct format;
   otherwise it returns non-zero.
