net@TUB.BITNET (Oliver Laumann) (07/05/88)
Although I think I understood what XGrabPointer(), XGrabButton(),
XAllowEvents() etc. are doing, I'm not quite sure how and when they are
actually used. For instance, am I right that the canonical way to do
pop-up menus (like those in uwm or xterm) is approximately like this:
o call XGrabButton() with an event_mask of ButtonPressed|
ButtonReleased|PointerMotion, and a pointer_mode of GrabModeSync;
o when the ButtonPressed event arrives:
o map the menu;
o invoke XAllowEvents() with an event_mode of AsyncPointer;
o let the user select something, wait for ButtonReleased, then
unmap the menu.
Is this a typical way XGrabButton() and XAllowEvents() are used?
Can you briefly describe a scenario where XAllowEvents() is invoked
with an event_mode other than AsyncPointer (i.e. SyncPointer or
ReplayPointer)?
Is calling XGrabButton() with a pointer_mode of GrabModeAsync
equivalent to calling it with a pointer_mode of GrabModeSync and
when the first event arrives immediately invoking XAllowEvents()
with an event_mode of AsyncPointer?
Thanks for your help.
--
Oliver Laumann net@TUB.BITNET net@tub.UUCPRWS@ZERMATT.LCS.MIT.EDU (Robert Scheifler) (07/06/88)
Date: Tue, 5 Jul 88 17:36:56 +0200
From: Oliver Laumann <net%TUB.BITNET@mitvma.mit.edu>
Is this a typical way XGrabButton() and XAllowEvents() are used?
For what you described, the Sync/AllowEvents didn't do you much good,
but you've got the basic idea.
Can you briefly describe a scenario where XAllowEvents() is invoked
with an event_mode other than AsyncPointer (i.e. SyncPointer or
ReplayPointer)?
A window manager might want to use the first click of a button in a
window to set the input focus there, but still pass the click through
to the application; Replay can be used for that.
If one of the actions to be performed is to change the input focus, then
one would use Sync (both in the grab and in the AllowEvents) to freeze
input until you have a chance to actually move the input focus.
Depending on what your UI is, you may have to issue a GrabPointer during
the grab, to prevent the grab from being released prematurely. For
example, if you want focus change to occur on release of the grabbed
button, Sync alone isn't sufficient, because the button release will
release the grab automatically.
Is calling XGrabButton() with a pointer_mode of GrabModeAsync
equivalent to calling it with a pointer_mode of GrabModeSync and
when the first event arrives immediately invoking XAllowEvents()
with an event_mode of AsyncPointer?
Not quite. If you don't also freeze the keyboard, then with Sync,
keyboard events can come "out of sequence" from pointer events
until your AllowEvents is executed.