Re: [gtk-vnc-devel] PATCH: key state tracking to avoid various bugs

["Daniel P. Berrange" <berrange redhat com>]

On Wed, Jan 09, 2008 at 08:24:35PM +0000, Daniel P. Berrange wrote:
> There are various problems with the VNC protocol and GTK relating to key
> state tracking. The VNC protocol has no concept of modifier keys, nor a
> way to reset key state. So if a client looses focus while one or more
> keys are pressed down, the server will never see any 'release' event for
> them. This is particularly troublesome with modifiers because it will 
> appear that Ctlr or Alt is stuck down and you'll get really wierd behaviour
> with keyboard shortcuts in your guest activating.
> 
> Second, GTK has the 'feature' where by it compresses  sequential press+release
> events for the same key. So if you hold down the 'a' key long enough to get
> keyboard repeat running, instead of down+up, down+up, down+up you'll merely
> get down,down,down,...,down+up.  This seriously annoys some VNC servers,
> in particular the Xen paravirt framebuffer will ignore the repeated down
> events.  
> 
> So this patch introduces  keystate tracking. This is then used in two cases
> to send extra fake events. If we get two sequential down events for the same
> key we will send an extra fake 'up' event before the extra down event. If
> we get a focus-out event, we will send fake 'up' events for all currently held
> down keys.  The state tracking also ensures that if the key is still held
> when focusin occurs, we won't get duplicated 'up' events.
> 
> I posted a similar patch quite a while ago, and Anthony suggested trying to
> hook into the mapping-notify event, but GTK doesn't expose this to apps,
> and we need to track state anyway to work around the GTK key repeat insanity

FYI I had pretty much identical code to this in the original virt-manager
VNC widget & it worked pretty reliably. The RealVNC viewer program also
has a near identical approach to this problem - albeit without need of
the GTK key-repeat hack since they don't use GTK.

Dan.
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