[PATCH] Reset X/Y hist on multi finger transition to fix jumps

[chris at cnpbagwell.com]

From: Chris Bagwell <chris at cnpbagwell.com>

Most modern track 1st finger during multi-touch.  If
first finger is lifted then a jump will occur as X/Y
transition to next finger location.  Resetting X/Y history
as each finger is lifted will hide this transition.

Synaptics hw specs claim older hardware report X/Y
values that are average point between multi-fingers
which can cause unwanted jump.  Reset X/Y history
during transition to new fingers to hide this as
well.

Signed-off-by: Chris Bagwell <chris at cnpbagwell.com>
---
 src/synaptics.c    |    3 ++-
 src/synapticsstr.h |    1 +
 2 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/src/synaptics.c b/src/synaptics.c
index aa14f76..99b16cc 100644
--- a/src/synaptics.c
+++ b/src/synaptics.c
@@ -1724,7 +1724,7 @@ ComputeDeltas(SynapticsPrivate *priv, const struct SynapticsHwState *hw,
     if (inside_area && moving_state && !priv->palm &&
 	!priv->vert_scroll_edge_on && !priv->horiz_scroll_edge_on &&
 	!priv->vert_scroll_twofinger_on && !priv->horiz_scroll_twofinger_on &&
-	!priv->circ_scroll_on) {
+	!priv->circ_scroll_on && priv->prevFingers == hw->numFingers) {
 	/* FIXME: Wtf?? what's with 13? */
 	delay = MIN(delay, 13);
 	if (priv->count_packet_finger > 3) { /* min. 3 packets */
@@ -1794,6 +1794,7 @@ ComputeDeltas(SynapticsPrivate *priv, const struct SynapticsHwState *hw,
     } else {				    /* reset packet counter */
 	priv->count_packet_finger = 0;
     }
+    priv->prevFingers = hw->numFingers;
 
     *dxP = dx;
     *dyP = dy;
diff --git a/src/synapticsstr.h b/src/synapticsstr.h
index b4a72aa..caa0476 100644
--- a/src/synapticsstr.h
+++ b/src/synapticsstr.h
@@ -218,6 +218,7 @@ typedef struct _SynapticsPrivateRec
     int palm;				/* Set to true when palm detected, reset to false when
 					   palm/finger contact disappears */
     int prev_z;				/* previous z value, for palm detection */
+    int prevFingers;			/* previous numFingers, for transition detection */
     int avg_width;			/* weighted average of previous fingerWidth values */
     double horiz_coeff;                 /* normalization factor for x coordintes */
     double vert_coeff;                  /* normalization factor for y coordintes */
-- 
1.7.2