Manual Pages for UNIX Darwin command on man grab

grab(n) Tk Built-In Commands grab(n)

NAME

grab - Confine pointer and keyboard events to a window sub-tree

SYNOPSIS

ggrraabb ?-gglloobbaall? window

ggrraabb option ?arg arg ...?

DESCRIPTION

This command implements simple pointer and keyboard grabs for Tk. Tk's

grabs are different than the grabs described in the Xlib documentation.

When a grab is set for a particular window, Tk restricts all pointer

events to the grab window and its descendants in Tk's window hierarchy.

Whenever the pointer is within the grab window's subtree, the pointer

will behave exactly the same as if there had been no grab at all and

all events will be reported in the normal fashion. When the pointer is outside window's tree, button presses and releases and mouse motion events are reported to window, and window entry and window exit events

are ignored. The grab subtree ``owns'' the pointer: windows outside

the grab subtree will be visible on the screen but they will be insen-

sitive until the grab is released. The tree of windows underneath the

grab window can include top-level windows, in which case all of those

top-level windows and their descendants will continue to receive mouse

events during the grab.

Two forms of grabs are possible: local and global. A local grab

affects only the grabbing application: events will be reported to

other applications as if the grab had never occurred. Grabs are local

by default. A global grab locks out all applications on the screen, so

that only the given subtree of the grabbing application will be sensi-

tive to pointer events (mouse button presses, mouse button releases, pointer motions, window entries, and window exits). During global

grabs the window manager will not receive pointer events either.

During local grabs, keyboard events (key presses and key releases) are

delivered as usual: the window manager controls which application receives keyboard events, and if they are sent to any window in the

grabbing application then they are redirected to the focus window.

During a global grab Tk grabs the keyboard so that all keyboard events

are always sent to the grabbing application. The ffooccuuss command is

still used to determine which window in the application receives the

keyboard events. The keyboard grab is released when the grab is

released. Grabs apply to particular displays. If an application has windows on

multiple displays then it can establish a separate grab on each dis-

play. The grab on a particular display affects only the windows on

that display. It is possible for different applications on a single

display to have simultaneous local grabs, but only one application can

have a global grab on a given display at once.

The ggrraabb command can take any of the following forms:

ggrraabb ?-gglloobbaall? window

Same as ggrraabb sseett, described below. ggrraabb ccuurrrreenntt ?window?

If window is specified, returns the name of the current grab

window in this application for window's display, or an empty string if there is no such window. If window is omitted, the command returns a list whose elements are all of the windows

grabbed by this application for all displays, or an empty string

if the application has no grabs.

ggrraabb rreelleeaassee window

Releases the grab on window if there is one, otherwise does

nothing. Returns an empty string.

ggrraabb sseett ?-gglloobbaall? window

Sets a grab on window. If -gglloobbaall is specified then the grab is

global, otherwise it is local. If a grab was already in effect

for this application on window's display then it is automati-

cally released. If there is already a grab on window and it has

the same global/local form as the requested grab, then the com-

mand does nothing. Returns an empty string. ggrraabb ssttaattuuss window

Returns nnoonnee if no grab is currently set on window, llooccaall if a

local grab is set on window, and gglloobbaall if a global grab is set.

BUGS

It took an incredibly complex and gross implementation to produce the

simple grab effect described above. Given the current implementation,

it isn't safe for applications to use the Xlib grab facilities at all

except through the Tk grab procedures. If applications try to manipu-

late X's grab mechanisms directly, things will probably break.

If a single process is managing several different Tk applications, only

one of those applications can have a local grab for a given display at

any given time. If the applications are in different processes, this restriction doesn't exist. KKEEYYWWOORRDDSS