Input: MT - add support for balanced slot assignment
Some devices are not fast enough to differentiate between a fast-moving
contact and a new contact. This problem cannot be fully resolved because
information is truly missing, but it is possible to safe-guard against
obvious mistakes by restricting movement with a maximum displacement.
The new problem formulation for dmax > 0 cannot benefit from the speedup
for positive definite matrices, but since the convergence is faster, the
result is about the same. For a handful of contacts, the latency difference
is truly negligible.
Suggested-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Tested-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Henrik Rydberg <rydberg@bitmath.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
diff --git a/drivers/input/input-mt.c b/drivers/input/input-mt.c
index fbe29fc..cb150a1 100644
--- a/drivers/input/input-mt.c
+++ b/drivers/input/input-mt.c
@@ -293,7 +293,7 @@
}
EXPORT_SYMBOL(input_mt_sync_frame);
-static int adjust_dual(int *begin, int step, int *end, int eq)
+static int adjust_dual(int *begin, int step, int *end, int eq, int mu)
{
int f, *p, s, c;
@@ -311,9 +311,10 @@
s = *p;
c = (f + s + 1) / 2;
- if (c == 0 || (c > 0 && !eq))
+ if (c == 0 || (c > mu && (!eq || mu > 0)))
return 0;
- if (s < 0)
+ /* Improve convergence for positive matrices by penalizing overcovers */
+ if (s < 0 && mu <= 0)
c *= 2;
for (p = begin; p != end; p += step)
@@ -322,23 +323,24 @@
return (c < s && s <= 0) || (f >= 0 && f < c);
}
-static void find_reduced_matrix(int *w, int nr, int nc, int nrc)
+static void find_reduced_matrix(int *w, int nr, int nc, int nrc, int mu)
{
int i, k, sum;
for (k = 0; k < nrc; k++) {
for (i = 0; i < nr; i++)
- adjust_dual(w + i, nr, w + i + nrc, nr <= nc);
+ adjust_dual(w + i, nr, w + i + nrc, nr <= nc, mu);
sum = 0;
for (i = 0; i < nrc; i += nr)
- sum += adjust_dual(w + i, 1, w + i + nr, nc <= nr);
+ sum += adjust_dual(w + i, 1, w + i + nr, nc <= nr, mu);
if (!sum)
break;
}
}
static int input_mt_set_matrix(struct input_mt *mt,
- const struct input_mt_pos *pos, int num_pos)
+ const struct input_mt_pos *pos, int num_pos,
+ int mu)
{
const struct input_mt_pos *p;
struct input_mt_slot *s;
@@ -352,7 +354,7 @@
y = input_mt_get_value(s, ABS_MT_POSITION_Y);
for (p = pos; p != pos + num_pos; p++) {
int dx = x - p->x, dy = y - p->y;
- *w++ = dx * dx + dy * dy;
+ *w++ = dx * dx + dy * dy - mu;
}
}
@@ -393,17 +395,24 @@
* @slots: the slot assignment to be filled
* @pos: the position array to match
* @num_pos: number of positions
+ * @dmax: maximum ABS_MT_POSITION displacement (zero for infinite)
*
* Performs a best match against the current contacts and returns
* the slot assignment list. New contacts are assigned to unused
* slots.
*
+ * The assignments are balanced so that all coordinate displacements are
+ * below the euclidian distance dmax. If no such assignment can be found,
+ * some contacts are assigned to unused slots.
+ *
* Returns zero on success, or negative error in case of failure.
*/
int input_mt_assign_slots(struct input_dev *dev, int *slots,
- const struct input_mt_pos *pos, int num_pos)
+ const struct input_mt_pos *pos, int num_pos,
+ int dmax)
{
struct input_mt *mt = dev->mt;
+ int mu = 2 * dmax * dmax;
int nrc;
if (!mt || !mt->red)
@@ -413,8 +422,8 @@
if (num_pos < 1)
return 0;
- nrc = input_mt_set_matrix(mt, pos, num_pos);
- find_reduced_matrix(mt->red, num_pos, nrc / num_pos, nrc);
+ nrc = input_mt_set_matrix(mt, pos, num_pos, mu);
+ find_reduced_matrix(mt->red, num_pos, nrc / num_pos, nrc, mu);
input_mt_set_slots(mt, slots, num_pos);
return 0;