[client] x11: Find and use the correct valuators for mouse axes

Using the first two valuators present in the event is incorrect.  Events
with only one valuator set, such as those sent by the Xorg evdev driver
when the mouse moved along one axis only, were being discarded.  On the
other hand, mice with multiple scroll wheels may be able to emit events
with two scroll wheel valuators set.

The XInput2 specification is light on details, but "Rel X" and "Rel Y"
appear to be the de facto standard names for the motion valuators.  If
valuators with those labels are not found, fall back to using valuators
with numbers 0 and 1.

client/displayservers/X11/x11.c

@@ -96,6 +96,8 @@ static bool x11Init(const LG_DSInitParams params)
   int event, error;
 
   memset(&x11, 0, sizeof(x11));
+  x11.xValuator = -1;
+  x11.yValuator = -1;
   x11.display = XOpenDisplay(NULL);
 
   XSetWindowAttributes swa =
@@ -289,24 +291,39 @@ static bool x11Init(const LG_DSInitParams params)
     goto fail_window;
   }
 
+  Atom rel_x = XInternAtom(x11.display, "Rel X", True);
+  Atom rel_y = XInternAtom(x11.display, "Rel Y", True);
+
   bool havePointer  = false;
   bool haveKeyboard = false;
   for(int i = 0; i < count; ++i)
   {
     /* look for the master pointing device */
     if (!havePointer && devinfo[i].use == XIMasterPointer)
+    {
       for(int j = 0; j < devinfo[i].num_classes; ++j)
       {
         XIAnyClassInfo *cdevinfo =
           (XIAnyClassInfo *)(devinfo[i].classes[j]);
         if (cdevinfo->type == XIValuatorClass)
         {
-          havePointer = true;
+          XIValuatorClassInfo *vdevinfo = (XIValuatorClassInfo *)cdevinfo;
-          x11.pointerDev = devinfo[i].deviceid;
+          if (vdevinfo->label == rel_x || (!vdevinfo->label &&
-          break;
+              vdevinfo->number == 0 && vdevinfo->mode == XIModeRelative))
+            x11.xValuator = vdevinfo->number;
+          else if (vdevinfo->label == rel_y || (!vdevinfo->label &&
+              vdevinfo->number == 1 && vdevinfo->mode == XIModeRelative))
+            x11.yValuator = vdevinfo->number;
         }
       }
 
+      if (x11.xValuator >= 0 && x11.yValuator >= 0)
+      {
+        havePointer = true;
+        x11.pointerDev = devinfo[i].deviceid;
+      }
+    }
+
     /* look for the master keyboard device */
     if (!haveKeyboard && devinfo[i].use == XIMasterKeyboard)
       for(int j = 0; j < devinfo[i].num_classes; ++j)
@@ -817,31 +834,37 @@ static void x11GenericEvent(XGenericEventCookie *cookie)
         return;
 
       XIRawEvent *raw = cookie->data;
-      double raw_axis[2];
+      double raw_axis[2] = { 0 };
-      double axis[2];
+      double axis[2] = { 0 };
 
       /* select the active validators for the X & Y axis */
       double *valuator = raw->valuators.values;
       double *r_value  = raw->raw_values;
-      int    count     = 0;
+      bool   has_axes  = false;
       for(int i = 0; i < raw->valuators.mask_len * 8; ++i)
       {
         if (XIMaskIsSet(raw->valuators.mask, i))
         {
-          raw_axis[count] = *r_value;
+          if (i == x11.xValuator)
-          axis    [count] = *valuator;
+          {
-          ++count;
+            raw_axis[0] = *r_value;
-
+            axis    [0] = *valuator;
-          if (count == 2)
+            has_axes = true;
-            break;
+          }
+          else if (i == x11.yValuator)
+          {
+            raw_axis[1] = *r_value;
+            axis    [1] = *valuator;
+            has_axes = true;
+          }
 
           ++valuator;
           ++r_value;
         }
       }
 
-      /* filter out scroll wheel and other events */
+      /* filter out events with no axis data */
-      if (count < 2)
+      if (!has_axes)
         return;
 
       /* filter out duplicate events */

client/displayservers/X11/x11.h

@@ -38,6 +38,8 @@ struct X11DSState
 
   int pointerDev;
   int keyboardDev;
+  int xValuator;
+  int yValuator;
 
   bool pointerGrabbed;
   bool keyboardGrabbed;