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77 lines
3.5 KiB
Go
77 lines
3.5 KiB
Go
/*
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Package xevent provides an event handler interface for attaching callback
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functions to X events, and an implementation of an X event loop.
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The X event loop
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One of the biggest conveniences offered by xgbutil is its event handler system.
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That is, the ability to attach an arbitrary callback function to any X event.
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In order for such things to work, xgbutil needs to control the main X event
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loop and act as a dispatcher for all event handlers created by you.
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To run the X event loop, use xevent.Main or xevent.MainPing. The former
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runs a normal event loop in the current goroutine and processes events. The
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latter runs the event loop in a new goroutine and returns a pingBefore and
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a pingAfter channel. The pingBefore channel is sent a benign value right before
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an event is dequeued, and the pingAfter channel is sent a benign value right
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after after all callbacks for that event have finished execution. These
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synchronization points in the main event loop can be combined with a 'select'
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statement to process data from other input sources. An example of this is given
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in the documentation for the MainPing function. A complete example called
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multiple-source-event-loop can also be found in the examples directory of the
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xgbutil package.
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To quit the main event loop, you may use xevent.Quit, but there is nothing
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inherently wrong with stopping dead using os.Exit. xevent.Quit is provided for
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your convenience should you need to run any clean-up code after the main event
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loop returns.
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The X event queue
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xgbutil's event queue contains values that are either events or errors. (Never
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both and never neither.) Namely, errors are received in the event loop from
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unchecked requests. (Errors generated by checked requests are guaranteed to be
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returned to the caller and are never received in the event loop.) Also, a
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default error handler function can be set with xevent.ErrorHandlerSet.
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To this end, xgbutil's event queue can be inspected. This is advantageous when
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information about what events will be processed in the future could be helpful
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(i.e., if there is an UnmapNotify event waiting to be processed.) The event
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queue can also be manipulated to facilitate event compression. (Two events that
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are common candidates for compression are ConfigureNotify and MotionNotify.)
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Detach events
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Whenever a window can no longer receive events (i.e., when it is destroyed),
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all event handlers related to that window should be detached. (If this is
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omitted, then Go's garbage collector will not be able to reuse memory occupied
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by the now-unused event handlers for that window.) Moreover, its possible that
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a window id can be reused after it has been discarded, which could result in
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odd behavior in your application.
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To detach a window from all event handlers in the xevent package, use
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xevent.Detach. If you're also using the keybind and mousebind packages, you'll
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need to call keybind.Detach and mousebind.Detach too. So to detach your window
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from all possible event handlers in xgbutil, use something like:
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xevent.Detach(XUtilValue, your-window-id)
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keybind.Detach(XUtilValue, your-window-id)
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mousebind.Detach(XUtilValue, your-window-id)
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Quick example
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A small example that shows how to respond to ConfigureNotify events sent to
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your-window-id.
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xevent.ConfigureNotifyFun(
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func(X *xgbutil.XUtil, e xevent.ConfigureNotifyEvent) {
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fmt.Printf("(%d, %d) %dx%d\n", e.X, e.Y, e.Width, e.Height)
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}).Connect(XUtilValue, your-window-id)
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More examples
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The xevent package is used in several of the examples in the examples directory
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in the xgbutil package.
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*/
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package xevent
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