x11: Fix duplicate Xinput2 event reception

Passing True for owner_events in the XGrabPointer call makes all
XI_RawMotion events appear in the queue twice, with the only difference
between them being the value of XGenericEventCookie::cookie. These have
always been filtered out by a check in the XI_RawMotion handler,
however with a mouse that polls at more than 1 kHz frequency, there
also exist legitimate events that appear indistinguishable from these
duplicated events. These must not be filtered out, otherwise the
pointer may move at an inconsistent speed, appearing like a bad pointer
acceleration implementation.

Change owner_events to False in the XGrabPointer and remove the
duplicate event detection code to fix this.

Signed-off-by: Torge Matthies <openglfreak@googlemail.com>
(cherry picked from commit f18b5656f6f859e4d4e096d290afd9fae884a5b8)

src/video/x11/SDL_x11mouse.h

@@ -30,7 +30,6 @@ typedef struct SDL_XInput2DeviceInfo
     double minval[2];
     double maxval[2];
     double prev_coords[2];
-    Time prev_time;
     struct SDL_XInput2DeviceInfo *next;
 } SDL_XInput2DeviceInfo;
 

src/video/x11/SDL_x11window.c

@@ -1624,7 +1624,7 @@ void X11_SetWindowMouseGrab(_THIS, SDL_Window *window, SDL_bool grabbed)
 
             /* Try for up to 5000ms (5s) to grab. If it still fails, stop trying. */
             for (attempts = 0; attempts < 100; attempts++) {
-                result = X11_XGrabPointer(display, data->xwindow, True, mask, GrabModeAsync,
+                result = X11_XGrabPointer(display, data->xwindow, False, mask, GrabModeAsync,
                                           GrabModeAsync, data->xwindow, None, CurrentTime);
                 if (result == GrabSuccess) {
                     data->mouse_grabbed = SDL_TRUE;

src/video/x11/SDL_x11xinput2.c

@@ -294,10 +294,6 @@ int X11_HandleXinput2Event(SDL_VideoData *videodata, XGenericEventCookie *cookie
         parse_valuators(rawev->raw_values, rawev->valuators.mask,
                         rawev->valuators.mask_len, coords, 2);
 
-        if ((rawev->time == devinfo->prev_time) && (coords[0] == devinfo->prev_coords[0]) && (coords[1] == devinfo->prev_coords[1])) {
-            return 0; /* duplicate event, drop it. */
-        }
-
         for (i = 0; i < 2; i++) {
             if (devinfo->relative[i]) {
                 processed_coords[i] = coords[i];
@@ -309,7 +305,6 @@ int X11_HandleXinput2Event(SDL_VideoData *videodata, XGenericEventCookie *cookie
         SDL_SendMouseMotion(mouse->focus, mouse->mouseID, 1, (int)processed_coords[0], (int)processed_coords[1]);
         devinfo->prev_coords[0] = coords[0];
         devinfo->prev_coords[1] = coords[1];
-        devinfo->prev_time = rawev->time;
         return 1;
     } break;