On Tue, Jan 09, 2018 at 07:18:31PM -0500, David Bokan wrote: > Hello, > > Please bear with me as I'm utterly new to X - I'm trying to debug an issue > in Chromium when using xtest. I'm not sure if the bug is in Chromium, X, or > XTest or some combination of the three. > > There's two things that are puzzling me: > > 1) When I click mouse button 1 on a physical device, it seems that there's > some kind of grab going on: I get an XI_Enter event with NotifyGrab and an > XI_Leave with NotifyUngrab. This kind of makes sense except that I've > disabled the explicit device grab (XIGrabDevice) and we don't have any > passive grabs that I can see. So where is this grab coming from? If I press > down and move the pointer out of the window I continue to see motion events.
it's part of the core protocol functionality, whenever a button event is delivered to a client it activates and implicit passive grab for that button. google/grep for "implicit passive grab", you should find a few things. > I tried to make a simple app to repro but couldn't. Using XIGrabButton > doesn't cause XI_Enter/Leave events if the click is with in the window. > So...where could this behavior be coming from? Figuring out how to > reproduce this would help me debug the issue below. > > 2) This is the real issue I'm debugging. Given the above XI_Enter/Leave > behavior on mouse buttons, It seems that using xtest causes us to get an > extra pair of XI_Enter and XI_Leave events on a mouse down with deviceid == > 4 (xtest pointer) - in addition to the regular ones we get as described > above for the master pointer. > > I can kind of repro this in a test app by using XIGrabButton on deviceid=4. > This causes me to get the crossing events with deviceid=4 but I don't get a > second pair for the master pointer. I'd have to page all the details into my brain again, but IIRC grabbing a slave device detaches it from the master device for the duration of the grab. so for that time being, the event sequence is a bit different. It shouldn't be different for xtest devices, the grab code doesn't care about whether it's an xtest device or some other device. > Any idea what might be happening or advice on how to dig deeper? Anything I > could try (e.g. is there a way to clear all passive grabs?) you can break grabs forcibly with the xkb 'grab:break_actions' action which I think is then mapped to ctrl+alt+keypad /. That's a debugging feature though, not something from the client. Cheers, Peter _______________________________________________ xorg@lists.x.org: X.Org support Archives: http://lists.freedesktop.org/archives/xorg Info: https://lists.x.org/mailman/listinfo/xorg Your subscription address: %(user_address)s
