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1995-07-25
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8KB
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199 lines
ggggrrrraaaabbbb((((nnnn)))) TTTTkkkk (((( )))) ggggrrrraaaabbbb((((nnnn))))
_________________________________________________________________
NNNNAAAAMMMMEEEE
grab - Confine pointer and keyboard events to a window sub-
tree
SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
ggggrrrraaaabbbb ?----gggglllloooobbbbaaaallll? _w_i_n_d_o_w
ggggrrrraaaabbbb _o_p_t_i_o_n ?arg arg ...? |
_________________________________________________________________
DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
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 _w_i_n_d_o_w's tree,
button presses and releases and mouse motion events are
reported to _w_i_n_d_o_w, 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 insensitive 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 sensitive 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 ffffooooccccuuuussss command
is still used to determine which window in the application
receives the keyboard events. The keyboard grab is released
Page 1 (printed 7/23/95)
ggggrrrraaaabbbb((((nnnn)))) TTTTkkkk (((( )))) ggggrrrraaaabbbb((((nnnn))))
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 display. 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 ggggrrrraaaabbbb command can take any of the following forms:
ggggrrrraaaabbbb ?----gggglllloooobbbbaaaallll? _w_i_n_d_o_w
Same as ggggrrrraaaabbbb sssseeeetttt, described below. |
ggggrrrraaaabbbb ccccuuuurrrrrrrreeeennnntttt ?_w_i_n_d_o_w? ||
If _w_i_n_d_o_w is specified, returns the name of the current |
grab window in this application for _w_i_n_d_o_w's display, |
or an empty string if there is no such window. If |
_w_i_n_d_o_w 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. |
ggggrrrraaaabbbb rrrreeeelllleeeeaaaasssseeee _w_i_n_d_o_w ||
Releases the grab on _w_i_n_d_o_w if there is one, otherwise |
does nothing. Returns an empty string. |
ggggrrrraaaabbbb sssseeeetttt ?----gggglllloooobbbbaaaallll? _w_i_n_d_o_w ||
Sets a grab on _w_i_n_d_o_w. If ----gggglllloooobbbbaaaallll is specified then |
the grab is global, otherwise it is local. If a grab |
was already in effect for this application on _w_i_n_d_o_w's |
display then it is automatically released. If there is |
already a grab on _w_i_n_d_o_w and it has the same |
global/local form as the requested grab, then the |
command does nothing. Returns an empty string. |
ggggrrrraaaabbbb ssssttttaaaattttuuuussss _w_i_n_d_o_w ||
Returns nnnnoooonnnneeee if no grab is currently set on _w_i_n_d_o_w, |
llllooooccccaaaallll if a local grab is set on _w_i_n_d_o_w, and gggglllloooobbbbaaaallll if a |
global grab is set.
BBBBUUUUGGGGSSSS
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 manipulate X's grab
mechanisms directly, things will probably break.
If a single process is managing several different Tk |
Page 2 (printed 7/23/95)
ggggrrrraaaabbbb((((nnnn)))) TTTTkkkk (((( )))) ggggrrrraaaabbbb((((nnnn))))
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.
KKKKEEEEYYYYWWWWOOOORRRRDDDDSSSS
grab, keyboard events, pointer events, window
Page 3 (printed 7/23/95)