Do not reuse tracking ids after a no-touch event

The fingers going away are important in the matching algorithm,
to correctly detect new fingers when placed close to a finger
in the process of leaving the surface. However, once a no-touch
has been confirmed, the tracking id should not be reused, should
a new finger appear close to the removal point.

This patch clears the tracking id of all removed or no-touch state
fingers, thereby reducing accidental jumps on touch to a minimum.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>

1 files changed, 11 insertions, 2 deletions

diff --git a/src/hwstate.c b/src/hwstate.c
index 1a68d28..d758d25 100644
--- a/src/hwstate.c
+++ b/src/hwstate.c
@@ -23,6 +23,8 @@
 #include <stdlib.h>
 #include <limits.h>
 
+#define NOTOUCH(hw, c) ((hw)->touch_major == 0 && (c)->has_touch_major)
+
 const int XMAX = 32767;
 
 void init_hwstate(struct HWState *s)
@@ -88,6 +90,8 @@ void modify_hwstate(struct HWState *s,
         /* setup distance matrix for finger id matching */
         for (j = 0; j < s->nfinger; j++) {
                 sid[j] = s->finger[j].id;
+                if (NOTOUCH(&s->finger[j].hw, caps))
+                        sid[j] = 0;
                 row = A + hw->nfinger * j;
                 for (i = 0; i < hw->nfinger; i++)
                         row[i] = dist2(&hw->finger[i], &s->finger[j].hw);
@@ -99,11 +103,16 @@ void modify_hwstate(struct HWState *s,
         for (i = 0; i < hw->nfinger; i++) {
                 j = hw2s[i];
                 id = j >= 0 ? sid[j] : 0;
-                while (!id)
-                        id = ++s->lastid;
+                if (!NOTOUCH(&hw->finger[i], caps))
+                        while (!id)
+                                id = ++s->lastid;
                 set_finger(&s->finger[i], &hw->finger[i], id, caps);
         }
 
+        /* clear remaining finger ids */
+        for (i = hw->nfinger; i < s->nfinger; i++)
+                s->finger[i].id = 0;
+
         s->button = hw->button;
         s->nfinger = hw->nfinger;
         s->evtime = hw->evtime;