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

[Peter Hutterer]

On Tue, Feb 07, 2012 at 01:07:07PM -0800, Chase Douglas wrote:
> 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>

verified, tm is always garbage and so is t in the same hunk. Swapping the
first to HIST_DELTA(0, i, millis) seems to do something (slowing down the
cursor, mainly) but I didn't look into it further.
Applied, commit is reverted, thanks.

   141d912..49f6109  master -> master

Derek, any comments?

Cheers,
  Peter

> ---
>  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
>