Avoid using too up-to-date values when restoring valuators

* src/xterm.c (xi_has_scroll_valuators): New function.
(xi_handle_device_changed): If the device changed event provides
scroll valuators, then use the values in there.  (bug#58980)

1 files changed, 117 insertions, 28 deletions

diff --git a/src/xterm.c b/src/xterm.c
index 71ff69ece4c..4178526c318 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -13026,6 +13026,23 @@ xi_get_scroll_valuator (struct xi_device_t *device, int number)
   return NULL;
 }
 
+/* Check if EVENT, a DeviceChanged event, contains any scroll
+   valuators.  */
+
+static bool
+xi_has_scroll_valuators (XIDeviceChangedEvent *event)
+{
+  int i;
+
+  for (i = 0; i < event->num_classes; ++i)
+    {
+      if (event->classes[i]->type == XIScrollClass)
+        return true;
+    }
+
+  return false;
+}
+
 #endif
 
 /* Handle EVENT, a DeviceChanged event.  Look up the device that
@@ -13049,21 +13066,93 @@ xi_handle_device_changed (struct x_display_info *dpyinfo,
 #endif
 
 #ifdef HAVE_XINPUT2_1
-  /* When a DeviceChange event is received for a master device, we
-     don't get any scroll valuators along with it.  This is possibly
-     an X server bug but I really don't want to dig any further, so
-     fetch the scroll valuators manually.  (bug#57020) */
+  if (xi_has_scroll_valuators (event))
+    {
+      /* Scroll valuators are provided by this event.  Use the values
+         provided in this event to populate the device's new scroll
+         valuator list, as if this event's is a SlaveSwitch event
+         caused by wheel movement, querying for the device info will
+         probably return newer values, leading to a delta of 0 being
+         computed when handling the subsequent XI_Motion event.
+         (bug#58980) */
 
-  x_catch_errors (dpyinfo->display);
-  info = XIQueryDevice (dpyinfo->display, event->deviceid,
-                        /* ndevices is always 1 if a deviceid is
-                           specified.  If the request fails, NULL will
-                           be returned.  */
-                        &ndevices);
-  x_uncatch_errors ();
+      device->valuators = xrealloc (device->valuators,
+                                    (event->num_classes
+                                     * sizeof *device->valuators));
+      device->scroll_valuator_count = 0;
+#ifdef HAVE_XINPUT2_2
+      device->direct_p = false;
+#endif
+
+      for (i = 0; i < event->num_classes; ++i)
+        {
+          switch (event->classes[i]->type)
+            {
+            case XIScrollClass:
+              scroll = (XIScrollClassInfo *) event->classes[i];
+
+              valuator = &device->valuators[device->scroll_valuator_count++];
+              valuator->horizontal = (scroll->scroll_type
+                                      == XIScrollTypeHorizontal);
+              valuator->invalid_p = true;
+              valuator->emacs_value = 0;
+              valuator->increment = scroll->increment;
+              valuator->number = scroll->number;
+              break;
+
+#ifdef HAVE_XINPUT2_2
+            case XITouchClass:
+              touch = (XITouchClassInfo *) event->classes[i];
+
+              if (touch->mode == XIDirectTouch)
+                device->direct_p = true;
+              break;
+#endif
+            }
+        }
+
+      /* Restore the values of any scroll valuators that we already
+         know about.  */
+
+      for (i = 0; i < event->num_classes; ++i)
+        {
+          switch (event->classes[i]->type)
+            {
+            case XIValuatorClass:
+              valuator_info = (XIValuatorClassInfo *) event->classes[i];
+
+              valuator = xi_get_scroll_valuator (device,
+                                                 valuator_info->number);
+              if (valuator)
+                {
+                  valuator->invalid_p = false;
+                  valuator->current_value = valuator_info->value;
+                  valuator->emacs_value = 0;
+                }
 
-  if (info)
+              break;
+            }
+        }
+    }
+  else
     {
+      /* When a DeviceChange event is received for a master device,
+         the X server sometimes does not send any scroll valuators
+         along with it.  This is possibly an X server bug but I really
+         don't want to dig any further, so fetch the scroll valuators
+         manually.  (bug#57020) */
+
+      x_catch_errors (dpyinfo->display);
+      info = XIQueryDevice (dpyinfo->display, event->deviceid,
+                            /* ndevices is always 1 if a deviceid is
+                               specified.  If the request fails, NULL will
+                               be returned.  */
+                            &ndevices);
+      x_uncatch_errors ();
+
+      if (!info)
+        return;
+
       device->valuators = xrealloc (device->valuators,
                                     (info->num_classes
                                      * sizeof *device->valuators));
@@ -13115,32 +13204,32 @@ xi_handle_device_changed (struct x_display_info *dpyinfo,
                 {
                   valuator->invalid_p = false;
                   valuator->current_value = valuator_info->value;
+                  valuator->emacs_value = 0;
                 }
 
               break;
             }
         }
 
-#ifdef HAVE_XINPUT2_2
-      /* The device is no longer a DirectTouch device, so
-         remove any touchpoints that we might have
-         recorded.  */
-      if (!device->direct_p)
-        {
-          tem = device->touchpoints;
+      XIFreeDeviceInfo (info);
+    }
+#endif
 
-          while (tem)
-            {
-              last = tem;
-              tem = tem->next;
-              xfree (last);
-            }
+#ifdef HAVE_XINPUT2_2
+  /* The device is no longer a DirectTouch device, so remove any
+     touchpoints that we might have recorded.  */
+  if (!device->direct_p)
+    {
+      tem = device->touchpoints;
 
-          device->touchpoints = NULL;
+      while (tem)
+        {
+          last = tem;
+          tem = tem->next;
+          xfree (last);
         }
-#endif
 
-      XIFreeDeviceInfo (info);
+      device->touchpoints = NULL;
     }
 #endif
 }