dix: Allocate MD's motion history to be large enough for potential valuators

Since we can't predict how many valuators may be in a future SD attached to an
MD, we need to preallocate a history buffer that is large enough to keep
MAX_VALUATORS coordinates per event.

In addition, the history buffer needs to memorize the coordinate ranges at the
time, thus requiring MDs to store (min_val, max_val, current_val, time)
instead of (current_val, time) for each motion history entry.

This commit only fixes the allocation.

dix/getevents.c

@@ -232,15 +232,25 @@ updateSlaveDeviceCoords(DeviceIntPtr master, DeviceIntPtr pDev)
 _X_EXPORT void
 AllocateMotionHistory(DeviceIntPtr pDev)
 {
+    int size;
     if (pDev->valuator->motion)
         xfree(pDev->valuator->motion);
 
     if (pDev->valuator->numMotionEvents < 1)
         return;
 
-    pDev->valuator->motion = xalloc(((sizeof(INT32) * pDev->valuator->numAxes)
+    /* An MD must have a motion history size large enough to keep all
-                                    + sizeof(Time)) *
+     * potential valuators, plus the respective range of the valuators.
-                                    pDev->valuator->numMotionEvents);
+     * 3 * INT32 for (min_val, max_val, curr_val))
+     */
+    if (pDev->isMaster)
+        size = sizeof(INT32) * 3 * MAX_VALUATORS;
+    else
+        size = sizeof(INT32) * pDev->valuator->numAxes;
+
+    size += sizeof(Time);
+
+    pDev->valuator->motion = xcalloc(pDev->valuator->numMotionEvents, size);
     pDev->valuator->first_motion = 0;
     pDev->valuator->last_motion = 0;
 }

include/inputstr.h

@@ -167,9 +167,9 @@ typedef struct _ValuatorClassRec {
     int		 	  numMotionEvents;
     int                   first_motion;
     int                   last_motion;
-    void                  *motion; /* motion history buffer */
+    void                  *motion; /* motion history buffer. Different layout
-
+                                      for MDs and SDs!*/
-    WindowPtr    	  motionHintWindow;
+    WindowPtr             motionHintWindow;
 
     AxisInfoPtr 	  axes;
     unsigned short	  numAxes;