[BUG] Duplicate Xi2 raw motion events when relative mouse input is enabled

SDL Development
1

Hello,

may I ask the SDL devs to pay attention to this bug?
https://bugzilla.libsdl.org/show_bug.cgi?id=2963

We’re recently bumped into it when porting our game engine from X11 to
SDL2. Any chance it might get fixed in time for 2.0.4?

Thanks.–
Best regards,
Victor Luchitz

2

The corresponding X.org bugreport
(https://bugs.freedesktop.org/show_bug.cgi?id=71609) says "Registering
for XI_RawMotion events on the root window makes XInput 2.1 or 2.2
client receive duplicate raw motion events when XGrabPointer is active
on the client window.“
I don’t really know how things work with X11/xinput, but why does SDL2
"register for XI_RawMotion events on the root window” and not on the
client window (which is the window handled by SDL, I guess)?

Cheers,
DanielOn 04/28/2015 11:31 AM, Victor Luchitz wrote:

Hello,

may I ask the SDL devs to pay attention to this bug?
https://bugzilla.libsdl.org/show_bug.cgi?id=2963

We’re recently bumped into it when porting our game engine from X11 to
SDL2. Any chance it might get fixed in time for 2.0.4?

Thanks.

3

Along with enabling Relative Mouse Motion the window is also grabbed.The
problem is that in X11_SetWindowGrab we grab the pointer by passing True to
owner_events and 0 for event_mask.

From Xlib documentation:

If owner_events is False, all generated pointer events are reported with
respect to grab_window and are reported only if selected by event_mask. If
owner_events is True and if a generated pointer event would normally be
reported to this client, it is reported as usual. Otherwise, the event is
reported with respect to the grab_window and is reported only if selected
by event_mask. For either value of owner_events, unreported events are
discarded.

So since we passed True to owner_events,we get duplicate events.By changing
True to False the problem is gone.

My Question is why X11_XGrabPointer inside X11_SetWindowGrab function
and X11_XGrabPointer inside X11_CaptureMouse act different?I think that
X11_GrabPointer inside X11_SetWIndowGrab should act the same as in
X11_CaptureMouse

X11_SetWindowGrab-------------------------------
X11_XGrabPointer(display, data->xwindow, True, 0, GrabModeAsync,
GrabModeAsync, data->xwindow, None, CurrentTime);

X11_CaptureMouse

const unsigned int mask = ButtonPressMask | ButtonReleaseMask |
PointerMotionMask | FocusChangeMask;
X11_XGrabPointer(display, data->xwindow, False, mask, GrabModeAsync,
GrabModeAsync,None, None, CurrentTime);

Dimitris Zenios

On Tue, Apr 28, 2015 at 4:28 PM, Daniel Gibson wrote:

The corresponding X.org bugreport (
https://bugs.freedesktop.org/show_bug.cgi?id=71609) says "Registering for
XI_RawMotion events on the root window makes XInput 2.1 or 2.2 client
receive duplicate raw motion events when XGrabPointer is active on the
client window.“
I don’t really know how things work with X11/xinput, but why does SDL2
"register for XI_RawMotion events on the root window” and not on the client
window (which is the window handled by SDL, I guess)?

Cheers,
Daniel

On 04/28/2015 11:31 AM, Victor Luchitz wrote:

Hello,

may I ask the SDL devs to pay attention to this bug?
https://bugzilla.libsdl.org/show_bug.cgi?id=2963

We’re recently bumped into it when porting our game engine from X11 to
SDL2. Any chance it might get fixed in time for 2.0.4?

Thanks.

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