Ubuntu Manpage: XScreenSaver - X11 Screen Saver extension client library

NAME

       XScreenSaver - X11 Screen Saver extension client library

SYNOPSIS

       #include <X11/extensions/scrnsaver.h>

       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 eventMask;      /∗ events */
       } XScreenSaverInfo;

       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;

       Bool XScreenSaverQueryExtension(Display *dpy, int *event_base_return, int *error_base_return);

       Status XScreenSaverQueryVersion(Display *dpy, int *major_version_return, int *minor_version_return);

       XScreenSaverInfo *XScreenSaverAllocInfo(void);

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

       void XScreenSaverSelectInput(Display *dpy, Drawable drawable, unsigned long mask);

       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);

       void XScreenSaverUnsetAttributes(Display *dpy, Drawable drawable);

       void XScreenSaverSaverRegister(Display *dpy, int screen, XID xid, Atom type);

       Status XScreenSaverUnregister(Display *dpy, int screen);

       Status XScreenSaverGetRegistered(Display *dpy, int screen, XID *xid, Atom *type);

       void XScreenSaverSuspend(Display *dpy, Bool suspend);

DESCRIPTION

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.

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.

XScreenSaverQueryExtension returns True if the XScreenSaver extension is available on the given display.
A client must call XScreenSaverQueryExtension before calling any other XScreenSaver function in order to
negotiate a compatible protocol version; otherwise the client will get undefined behavior (XScreenSaver
may or may not work).

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.

XScreenSaverQueryVersion returns True if the request succeeded; the values of the major and minor
protocol versions supported by the server are returned in major_version_return and minor_version_return .

XScreenSaverAllocInfo 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.

XScreenSaverQueryInfo returns information about the current state of the screen server in saver_info and
a non-zero value is returned. If the extension is not supported, saver_info is not changed and 0 is
returned.

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.

XScreenSaverSelectInput asks that events related to the screen saver 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.

XScreenSaverSetAttributes sets the attributes to be used the next time the external screen saver is
activated. If another client currently has the attributes set, a BadAccess 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).

XScreenSaverUnsetAttributes instructs the server to discard any previous screen saver window attributes
set by this client.

XScreenSaverRegister 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.

XScreenSaverUnregister 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.

XScreenSaverGetRegistered 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.

XScreenSaverSuspend temporarily suspends the screensaver and DPMS timer if suspend is 'True', and
restarts the timer if suspend is 'False'.
This function should be used by applications that don't want the screensaver or DPMS to become activated
while they're for example in the process of playing a media sequence, or are otherwise continuously
presenting visual information to the user while in a non-interactive state. This function is not intended
to be called by an external screensaver application.
If XScreenSaverSuspend is called multiple times with suspend set to 'True', it must be called an equal
number of times with suspend set to 'False' in order for the screensaver timer to be restarted. This
request has no affect if a client tries to resume the screensaver without first having suspended it.
XScreenSaverSuspend can thus not be used by one client to resume the screensaver if it's been suspended
by another client.
If a client that has suspended the screensaver becomes disconnected from the X server, the screensaver
timer will automatically be restarted, unless it's still suspended by another client. Suspending the
screensaver timer doesn't prevent the screensaver from being forceably activated with the
ForceScreenSaver request, or a DPMS mode from being set with the DPMSForceLevel request.
XScreenSaverSuspend also doesn't deactivate the screensaver or DPMS if either is active at the time the
request to suspend them is received by the X server. But once they've been deactivated, they won't
automatically be activated again, until the client has canceled the suspension.

ERRORS

       XScreenSaverSelectInput, XScreenSaverQueryInfo, XScreenSaverSetAttributes and XScreenSaverUnsetAttributes
       will generate a BadDrawable error if drawable is not a valid drawable identifier.  If any undefined  bits
       are set in event-mask, a BadValue error is generated by XScreenSaverSelectInput .

AVAILABILITY

       XScreenSaverSuspend  is  available  in  version  1.1  and later versions of the X Screen Saver Extension.
       Version 1.1 was first released with X11R7.1.

AUTHORS

       Jim Fulton and Keith Packard.

STABILITY

       This API is considered as experimental.  The Xss library  major  revision  may  be  incremented  whenever
       incompatible changes are done to the API without notice.  Use with care.