117 lines
5.4 KiB
HTML
117 lines
5.4 KiB
HTML
<HTML><HEAD><TITLE>Tk Built-In Commands - grab manual page</TITLE></HEAD>
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<BODY bgcolor = #c3c3ff>
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<H2><IMG ALIGN=BOTTOM SRC="./Img/ManPageBlue.gif"> grab</H2>
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<I>Confine pointer and keyboard events to a window sub-tree</I><P><IMG ALIGN=TOP SRC="./Img/line-red.gif">
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<H3><A NAME="M2">SYNOPSIS</A></H3>
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(<B>grab </B><I>window</I>)<BR>
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(<B>grab </B><B>:global</B> <I>window</I>)<BR>
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(<B>grab </B><I>option </I>?<I>arg arg </I>...?)<BR>
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<H3><A NAME="M3">DESCRIPTION</A></H3>
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This procedure implements simple pointer and keyboard grabs for Tk.
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Tk's grabs are different than the grabs
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described in the Xlib documentation.
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When a grab is set for a particular window, Tk restricts all pointer
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events to the grab window and its descendants in Tk's window hierarchy.
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Whenever the pointer is within the grab window's subtree, the pointer
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will behave exactly the same as if there had been no grab at all
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and all events will be reported in the normal fashion.
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When the pointer is outside <I>window</I>'s tree, button presses and
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releases and
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mouse motion events are reported to <I>window</I>, and window entry
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and window exit events are ignored.
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The grab subtree ``owns'' the pointer:
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windows outside the grab subtree will be visible on the screen
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but they will be insensitive until the grab is released.
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The tree of windows underneath the grab window can include top-level
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windows, in which case all of those top-level windows
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and their descendants will continue to receive mouse events
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during the grab.
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<P>
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Two forms of grabs are possible: local and global.
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A local grab affects only the grabbing application: events will
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be reported to other applications as if the grab had never occurred.
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Grabs are local by default.
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A global grab locks out all applications on the screen,
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so that only the given subtree of the grabbing application will be
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sensitive to pointer events (mouse button presses, mouse button releases,
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pointer motions, window entries, and window exits).
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During global grabs the window manager will not receive pointer
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events either.
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<P>
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During local grabs, keyboard events (key presses and key releases)
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are delivered as usual: the window
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manager controls which application receives keyboard events, and
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if they are sent to any window in the grabbing application then they are
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redirected to the focus window.
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During a global grab Tk grabs the keyboard so that all keyboard events
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are always sent to the grabbing application.
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The <B><A HREF="./focus.n.html">focus</A></B> procedure is still used to determine which window in the
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application receives the keyboard events.
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The keyboard grab is released when the grab is released.
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<P>
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Grabs apply to particular displays. If an application has windows
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on multiple displays then it can establish a separate grab on each
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display.
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The grab on a particular display affects only the windows on
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that display.
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It is possible for different applications on a single display to have
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simultaneous local grabs, but only one application can have a global
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grab on a given display at once.
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<P>
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The <B>grab</B> procedure can take any of the following forms:
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<P>
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<DL>
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<DT><A NAME="M4">(<B>grab </B> <I>window</I>)</A><DD>
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<DT><A NAME="M5">(<B>grab </B><B>:global</B> <I>window</I>)</A><DD>
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Same as <B>grab set</B>, described below.
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<P>
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<DT><A NAME="M6">(<B>grab 'current </B>)</A><DD>
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<DT><A NAME="M7">(<B>grab 'current </B><I>window</I>)</A><DD>
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If <I>window</I> is specified, returns the name of the current grab
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window in this application for <I>window</I>'s display, or an empty
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string if there is no such window.
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If <I>window</I> is omitted, the procedure returns a list whose elements
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are all of the windows grabbed by this application for all displays,
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or an empty string if the application has no grabs.
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<P>
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<DT><A NAME="M8">(<B>grab 'release </B><I>window</I>)</A><DD>
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Releases the grab on <I>window</I> if there is one, otherwise does
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nothing. Returns an empty string.
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<P>
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<DT><A NAME="M9">(<B>grab 'set </B> <I>window</I>)</A><DD>
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<DT><A NAME="M10">(<B>grab 'set </B><B>:global</B> <I>window</I>)</A><DD>
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Sets a grab on <I>window</I>. If <B>:global</B> is specified then the
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grab is global, otherwise it is local.
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If a grab was already in effect for this application on
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<I>window</I>'s display then it is automatically released.
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If there is already a grab on <I>window</I> and it has the same
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global/local form as the requested grab, then the procedure
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does nothing. Returns an empty string.
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<P>
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<DT><A NAME="M11">(<B>grab 'status </B><I>window</I>)</A><DD>
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Returns <B>"none"</B> if no grab is currently set on <I>window</I>,
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<B>"local"</B> if a local grab is set on <I>window</I>, and
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<B>"global"</B> if a global grab is set.
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<P>
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</DL>
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<H3><A NAME="M12">BUGS</A></H3>
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It took an incredibly complex and gross implementation to produce
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the simple grab effect described above.
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Given the current implementation, it isn't safe for applications
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to use the Xlib grab facilities at all except through the Tk grab
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procedures.
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If applications try to manipulate X's grab mechanisms directly,
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things will probably break.
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<P>
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If a single process is managing several different Tk applications,
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only one of those applications can have a local grab for a given
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display at any given time. If the applications are in different
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processes, this restriction doesn't exist.
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<H3><A NAME="M13">SEE ALSO</A></H3>
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<B><A HREF="./focus.n.html">focus</A></B>
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<P><IMG ALIGN=TOP SRC="./Img/line-red.gif">
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<A HREF=./STk-hlp.html><IMG ALIGN=BOTTOM SRC="./Img/RefBookBlue.gif"> Back to the <B>STk</B> main page</A>
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</BODY></HTML>
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