Revise Xserver behaviour for issue:"First wheel event to unfocused window is missing with xinput2"

[cepelinas9000]

Describe the idea

Technically X11Libre/xserver#553 is not a bug , at least in literal sense. But digging deeper how GTK library implemented xinput2 scrolling, IT good be good idea tweak XIEnterEvent event and include XIValuators for all pointer axes to account for discontinuities. thus it would be minimal change in gtk to not miss first event.

It should be done because

It looks like most logical solution without added extra rountrips

What are the alternatives?

Ater XIEnterEvent requests data about device like I did or send unsolicited Motion event for scroll bars.

Additional context

See: X11Libre/xserver#553

Extra fields

• I have checked the existing New Ideas, RFCs Of The Core Team, Ideas Soon To Be Addressed and Someday Ideas
• I have read the Contributing Guidelines
• I'd like to work on this idea

[bmacho]

https://bugzilla.gnome.org/show_bug.cgi?id=750870#c3 and https://gitlab.gnome.org/GNOME/gtk/-/issues/558 and https://who-t.blogspot.com/2012/06/xi-21-protocol-design-issues.html are related.

As far as I gathered

• in gtk trackpad gestures support is put in xinput2
• xinput2 also implements smooth scrolling for mouse wheels but it has a lot of bugs around it, e.g. https://gitlab.gnome.org/GNOME/mutter/-/issues/3690 , so xinput2 is not used/disabled by default
• gnome/gtk claims that it is unfixable and won't fix it

Also, if one doesn't need smooth scrolling for mouse wheel but is fine with the "send one scroll event after 1 scroll step on mouse wheel" behavior, then it is already possible to use xinput2 and have gestures and scrolling in unfocused windows. Installing and running imwheel (intercepts mousewheel events) accomplishes that, although I don't know how it interacts with other bugs and heuristic workarounds here and there.

If xinput2 smooth scrolling turns out to be not fixable, then an alternative plan could be to decouple smooth scrolling and gestures. E.g. provide an option to use xinput2 without smooth scrolling. That would allow enabling xinput2 and trackpad gestures to everyone, and the choice would be between "no smooth scrolling" and "smooth scrolling with wheel bugs", and not about gestures.

[cepelinas9000]

Maybe there are additional corner, but my patch solving that problem: "Bug: Massive mouse wheel scrolling issue reset jump" with my patch.

[callmetango]

For the sake of completeness, here is the patch from @cepelinas9000 for GTK branch 3.24:

[callmetango]

diff --git a/gdk/x11/gdkdevice-xi2.c b/gdk/x11/gdkdevice-xi2.c
index 92c78e68d5..155653d6fb 100644
--- a/gdk/x11/gdkdevice-xi2.c
+++ b/gdk/x11/gdkdevice-xi2.c
@@ -932,6 +932,49 @@ _gdk_device_xi2_reset_scroll_valuators (GdkX11DeviceXI2 *device)
     }
 }
 
+void _gdk_device_xi2_try_X11_get_valuators_values(GdkX11DeviceXI2 *device,Display *xdisplay)
+{
+
+    int nreturn;
+    XIDeviceInfo *info = XIQueryDevice(xdisplay, device->device_id, &nreturn);
+
+    if (info == NULL){
+      return;
+    }
+
+    if (nreturn == 0){
+      if (info)  {
+        XIFreeDeviceInfo(info);
+      }
+      return;
+    }
+
+
+    for(int i = 0; i <  info->num_classes; i++ ) {
+        if (info->classes[i]->type == XIValuatorClass) {
+           XIValuatorClassInfo *v = (XIValuatorClassInfo *)info->classes[i];
+
+	   guint j;
+	   for (j = 0; j  < device->scroll_valuators->len; j++) {
+             ScrollValuator *scroll;
+	     scroll = &g_array_index (device->scroll_valuators, ScrollValuator, j);
+
+	     if (scroll->n_valuator == v->number){
+                scroll->last_value_valid = TRUE;
+		scroll->last_value = v->value;
+	     }
+
+	   }
+
+
+
+	}
+
+    }
+
+   XIFreeDeviceInfo(info);
+}
+
 void
 _gdk_device_xi2_unset_scroll_valuators (GdkX11DeviceXI2 *device)
 {
diff --git a/gdk/x11/gdkdevicemanager-xi2.c b/gdk/x11/gdkdevicemanager-xi2.c
index a65116a3c1..9fd6ee3352 100644
--- a/gdk/x11/gdkdevicemanager-xi2.c
+++ b/gdk/x11/gdkdevicemanager-xi2.c
@@ -2148,16 +2148,25 @@ gdk_x11_device_manager_xi2_translate_event (GdkEventTranslator *translator,
             xev->detail != XINotifyInferior && xev->mode != XINotifyPassiveUngrab &&
 	    gdk_window_get_window_type (window) == GDK_WINDOW_TOPLEVEL)
           {
-            if (gdk_device_get_device_type (source_device) != GDK_DEVICE_TYPE_MASTER)
-              _gdk_device_xi2_reset_scroll_valuators (GDK_X11_DEVICE_XI2 (source_device));
+            if (gdk_device_get_device_type (source_device) != GDK_DEVICE_TYPE_MASTER){
+	     
+              GdkX11DeviceXI2 *mdev = GDK_X11_DEVICE_XI2 (source_device);
+
+              _gdk_device_xi2_reset_scroll_valuators (mdev);
+              _gdk_device_xi2_try_X11_get_valuators_values(mdev,GDK_DISPLAY_XDISPLAY (display));
+
+	      }
             else
               {
                 GList *slaves, *l;
 
                 slaves = gdk_device_list_slave_devices (source_device);
 
-                for (l = slaves; l; l = l->next)
-                  _gdk_device_xi2_reset_scroll_valuators (GDK_X11_DEVICE_XI2 (l->data));
+                for (l = slaves; l; l = l->next) {
+                     GdkX11DeviceXI2 *mdev = GDK_X11_DEVICE_XI2 (l->data);
+                     _gdk_device_xi2_reset_scroll_valuators (mdev);
+                     _gdk_device_xi2_try_X11_get_valuators_values(mdev,GDK_DISPLAY_XDISPLAY (display));
+                }
 
                 g_list_free (slaves);
               }
diff --git a/gdk/x11/gdkprivate-x11.h b/gdk/x11/gdkprivate-x11.h
index 72039585e4..f60ecf3ebe 100644
--- a/gdk/x11/gdkprivate-x11.h
+++ b/gdk/x11/gdkprivate-x11.h
@@ -252,6 +252,9 @@ gboolean  _gdk_x11_device_xi2_get_scroll_delta    (GdkX11DeviceXI2    *device,
                                                    gdouble            *delta_ret);
 void     _gdk_device_xi2_reset_scroll_valuators   (GdkX11DeviceXI2    *device);
 
+void     _gdk_device_xi2_try_X11_get_valuators_values(GdkX11DeviceXI2 *mdev,
+                                                      Display *display);
+
 gdouble  gdk_x11_device_xi2_get_last_axis_value (GdkX11DeviceXI2 *device,
                                                  gint             n_axis);
 

[dec05eba]

For the window focus issue as described as the second issue here: https://who-t.blogspot.com/2012/06/xi-21-protocol-design-issues.html cant the server just use different valuator data for each window (or the window that client does XISelectEvents on, or the client)? then when the window receives focus again it will continue off where it was, instead of having its absolute value affected by things that happened outside it?

[cepelinas9000]

It can, but it just will be transformed to window level relative position. I'm afraid with this we will broke behavior excpectation.

[cepelinas9000]

Qt framework doing exactly same (only uses one request): https://github.com/qt/qtbase/blob/4fa8dfee5dd31433d22fdb449c1783e256931c8f/src/plugins/platforms/xcb/qxcbwindow.cpp#L2256