[PATCH xf86-input-synaptics 1/2] Revert "Replace the motion estimator"

[Chase Douglas]

The algorithm is completely wrong because it uses subtraction of
unsigned variables. The negative effects of this commit manifest in
cursor warps to edges or corners of the screen.

Since the algorithm has never worked right, previous testing must be
disregarded. Revert it until we have a tested algorithm.

This reverts commit b26125e412a130b7a8f8b6adf9ffc8e9cc8df42c.

Conflicts:

	src/synaptics.c

Signed-off-by: Chase Douglas <chase.douglas at canonical.com>
---
 src/synaptics.c |   72 +++---------------------------------------------------
 1 files changed, 4 insertions(+), 68 deletions(-)

diff --git a/src/synaptics.c b/src/synaptics.c
index 9937634..a4c1e5a 100644
--- a/src/synaptics.c
+++ b/src/synaptics.c
@@ -1891,70 +1891,6 @@ get_edge_speed(SynapticsPrivate *priv, const struct SynapticsHwState *hw,
     }
 }
 
-/*
- * Fit a line through the three most recent points in the motion
- * history and return relative co-ordinates.
- */
-static void regress(SynapticsPrivate *priv, const struct SynapticsHwState *hw,
-                    double *dx, double *dy, CARD32 start_time)
-{
-    int i;
-    int packet_count = MIN(priv->count_packet_finger, 3);
-    double ym = 0, xm = 0, tm = 0;
-    double yb1n = 0, xb1n = 0, b1d = 0, xb1, yb1;
-
-    /* If there's only one packet, we can't really fit a line.  However, we
-     * don't want to lose very short interactions with the pad, so we pass on
-     * an unfiltered delta using the current hardware position. */
-    if (packet_count == 1) {
-	*dx = hw->x - HIST(0).x;
-	*dy = hw->y - HIST(0).y;
-	return;
-    }
-
-    /*
-     * Using ordinary least squares, calculate best fit lines through the most
-     * recent (up to) 3 entries in the motion history.
-     *
-     * Because millis is unsigned, we do our subtractions in reverse order to
-     * ensure the result is always positive.  The end result is that our slope
-     * is the negative of the slope we actually want.
-     *
-     * Note: the X and Y axes are treated as independent data sets for
-     * simplicity.
-     */
-    for (i = 0; i < packet_count; i++) {
-	ym += HIST(i).y;
-	xm += HIST(i).x;
-	tm += HIST_DELTA(i, 0, millis);
-    }
-    ym /= packet_count;
-    tm /= packet_count;
-    xm /= packet_count;
-
-    for (i = 0; i < packet_count; i++) {
-	double t = HIST_DELTA(i, 0, millis);
-	yb1n += (t - tm) * (HIST(i).y - ym);
-	xb1n += (t - tm) * (HIST(i).x - xm);
-	b1d += (t - tm) * (t - tm);
-    }
-    xb1 = xb1n/b1d;
-    yb1 = yb1n/b1d;
-
-    /*
-     * Here we use the slope component (b1) of the regression line as a speed
-     * estimate, and calculate how far the contact would have moved between
-     * the current time (hw->millis) and the last time we output a delta
-     * (start_time).
-     *
-     * The negative is because the slope is going the exact wrong direction
-     * (see above).
-     */
-    *dx = -xb1 * (start_time - hw->millis);
-    *dy = -yb1 * (start_time - hw->millis);
-    return;
-}
-
 static void
 get_delta(SynapticsPrivate *priv, const struct SynapticsHwState *hw,
           edge_type edge, double *dx, double *dy)
@@ -1966,9 +1902,9 @@ get_delta(SynapticsPrivate *priv, const struct SynapticsHwState *hw,
     int x_edge_speed = 0;
     int y_edge_speed = 0;
 
-    /* regress() performs the actual motion prediction. */
-    regress(priv, hw, dx, dy, priv->last_motion_millis);
-    priv->last_motion_millis = hw->millis;
+    /* HIST is full enough: priv->count_packet_finger > 3 */
+    *dx = estimate_delta(hw->x, HIST(0).x, HIST(1).x, HIST(2).x);
+    *dy = estimate_delta(hw->y, HIST(0).y, HIST(1).y, HIST(2).y);
 
     if ((priv->tap_state == TS_DRAG) || para->edge_motion_use_always)
         get_edge_speed(priv, hw, edge, &x_edge_speed, &y_edge_speed);
@@ -2037,7 +1973,7 @@ ComputeDeltas(SynapticsPrivate *priv, const struct SynapticsHwState *hw,
      * POLL_MS declaration. */
     delay = MIN(delay, POLL_MS);
 
-    if (priv->count_packet_finger < 1) /* min. 1 packet, see regress() */
+    if (priv->count_packet_finger <= 3) /* min. 3 packets, see get_delta() */
         goto out; /* skip the lot */
 
     if (priv->moving_state == MS_TRACKSTICK)
-- 
1.7.8.3