XScreenSaver(3x)

NAME
XScreenSaver - X11 Screen Saver extension client library

SYNOPSIS
#include <X11/extension/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 event_mask;     /* 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_basep, int *error_basep);

Status XScreenSaverQueryVersion(Display *dpy, int *major_versionp, int *minor_versionp);

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);

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_versionp and minor_versionp .

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.

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 .

SEE ALSO
X(7)

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.