Version 1.0
Copyright © 1992 Massachusetts Institute of Technology and Network Computing Devices, Inc
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Table of Contents
Table of Contents
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.
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.
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 refered 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.
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 controlable.
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.
The Screen Saver extension is as follows:
In adition to the comon 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 |
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 interpretted:
| 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.
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.
Please refer to the X11 Protocol Encoding document as this document uses conventions established there.
The name of this extension is "SCREEN-SAVER".
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
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.
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,External} */
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 frome a SendEvent request */
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.