Further reduce arbitration priority of cursor devices

Cursor (puck) devices are typically left on the sensor and can emit
spurious events that can potentially cause the driver to steal "active"
status from another tool. In the past we'd only considered the case where
the active tool was a touch but it is reasonable to extend this logic to
other tool types. If a cursor emits a spurious event in the middle of a
pen dragging, for example, the drag will momentarily stop as the pen is
temporarily sent out of prox -- with potentially disasterous results.
Additionally, when the pen "returns" in prox on the next event, any
currently-applied pressure will be taken as the preload and result in
incorrect pressure scaling until the pen is removed from contact.

This commit removes the "IsTouch" conditions from the handling of
spurious cursor events in check_arbitrated_control. The result is that a
cursor will not be granted "active" status in preference to any other
tool (and will drop "active" status if gained after 100ms and while
no buttons are pressed).

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>

1 files changed, 18 insertions, 9 deletions

diff --git a/src/wcmCommon.c b/src/wcmCommon.c
index 689646c..17df7fc 100644
--- a/src/wcmCommon.c
+++ b/src/wcmCommon.c
@@ -854,29 +854,38 @@ static Bool check_arbitrated_control(InputInfoPtr pInfo, WacomDeviceStatePtr ds)
 
 	if (IsPad(priv)) {
 		/* Pad may never be the "active" pointer controller */
+		DBG(6, priv, "Event from pad; not yielding pointer control\n.");
 		return FALSE;
 	}
 
 	if (active == NULL || active->oldState.device_id == ds->device_id) {
-		DBG(11, priv, "Same device ID as active; allowing access.\n");
+		DBG(11, priv, "Event from active device; maintaining pointer control.\n");
 		return TRUE;
 	}
-	else if (IsCursor(active) && IsTouch(priv)) {
-		/* Cursor devices are often left idle in range, so allow touch to
-		 * grab control if the tool has not been used for some time.
+	else if (IsCursor(active)) {
+		/* Cursor devices are often left idle in range, so allow other devices
+		 * to grab control if the tool has not been used for some time.
 		 */
-		return (ds->time - active->oldState.time > 100) && (active->oldState.buttons == 0);
+		Bool yield = (ds->time - active->oldState.time > 100) && (active->oldState.buttons == 0);
+		DBG(6, priv, "Currently-active cursor %s idle; %s pointer control.\n",
+		    yield ? "is" : "is not", yield ? "yielding" : "not yielding");
+		return yield;
 	}
-	else if (IsTouch(active) && IsCursor(priv)) {
+	else if (IsCursor(priv)) {
 		/* An otherwise idle cursor may still occasionally jitter and send
-		 * events while the user is making active touches. Do not allow
-		 * the cursor to grab control in this particular case.
+		 * events while the user is actively using other tools or touching
+		 * the device. Do not allow the cursor to grab control in this
+		 * particular case.
 		 */
+		DBG(6, priv, "Event from non-active cursor; not yielding pointer control.\n");
 		return FALSE;
 	}
 	else {
 		/* Non-touch input has priority over touch in general */
-		return !IsTouch(priv);
+		Bool yield = !IsTouch(priv);
+		DBG(6, priv, "Event from non-active %s device; %s pointer control.\n",
+		    yield ? "non-touch" : "touch", yield ? "yielding" : "not yielding");
+		return yield;
 	}
 }