3 files changed, 18 insertions, 11 deletions

diff --git a/include/mtdev.h b/include/mtdev.h
index b759803..b621245 100644
--- a/include/mtdev.h
+++ b/include/mtdev.h
@@ -74,11 +74,14 @@
 
 #define MT_ABS_SIZE 11
 
+#define MT_ID_NULL      (-1)
+#define MT_ID_MIN       0
+#define MT_ID_MAX       65535
+
 /**
  * struct mt_caps - protocol capabilities of kernel device
  * @has_mtdata: true if the device has MT capabilities
  * @has_slot: true if the device sends MT slots
- * @nullid: tracking id used to represent null
  * @slot: slot event properties
  * @abs: ABS_MT event properties
  */
@@ -86,7 +89,6 @@ struct mtdev_caps {
         int has_mtdata;
         int has_slot;
         int has_abs[MT_ABS_SIZE];
-        int nullid;
         struct input_absinfo slot;
         struct input_absinfo abs[MT_ABS_SIZE];
 };
diff --git a/src/caps.c b/src/caps.c
index 1821bd7..0788acf 100644
--- a/src/caps.c
+++ b/src/caps.c
@@ -83,8 +83,10 @@ static int read_caps(struct mtdev_caps *cap, int fd)
 
         cap->has_mtdata = has_mt_data(cap);
 
-        if (cap->has_abs[MTDEV_TRACKING_ID])
-                cap->nullid = cap->abs[MTDEV_TRACKING_ID].minimum - 1;
+        if (!cap->has_abs[MTDEV_TRACKING_ID]) {
+                cap->abs[MTDEV_TRACKING_ID].minimum = MT_ID_MIN;
+                cap->abs[MTDEV_TRACKING_ID].maximum = MT_ID_MAX;
+        }
 
         default_fuzz(cap, MTDEV_POSITION_X, SN_COORD);
         default_fuzz(cap, MTDEV_POSITION_Y, SN_COORD);
diff --git a/src/core.c b/src/core.c
index 8df2477..55b62b6 100644
--- a/src/core.c
+++ b/src/core.c
@@ -89,9 +89,9 @@ static void solve(struct mtdev_state *state, const struct mtdev_caps *caps,
         /* update matched contacts and create new ones */
         foreach_bit(i, touch) {
                 j = n2s[i];
-                id = j >= 0 ? sid[j] : caps->nullid;
-                while (id == caps->nullid)
-                        id = ++state->lastid;
+                id = j >= 0 ? sid[j] : MT_ID_NULL;
+                if (id == MT_ID_NULL)
+                        id = state->lastid++ & MT_ID_MAX;
                 nid[i] = id;
         }
 }
@@ -125,7 +125,7 @@ static void assign_tracking_id(struct mtdev_state *state,
         solve(state, caps, sid, sx, sy, sn, nid, nx, ny, size, touch);
         for (i = 0; i < size; i++) {
                 data[i].abs[MTDEV_TRACKING_ID] =
-                        GETBIT(touch, i) ? nid[i] : caps->nullid;
+                        GETBIT(touch, i) ? nid[i] : MT_ID_NULL;
                 prop[i] |= BITMASK(MTDEV_TRACKING_ID);
         }
 }
@@ -289,10 +289,10 @@ static void apply_typeA_changes(struct mtdev_state *state,
                         filter_data(state, caps, &data[i], prop[i], slot);
                         push_slot_changes(state, &data[i], prop[i], slot, syn);
                         SETBIT(used, slot);
-                        id = caps->nullid;
+                        id = MT_ID_NULL;
                         break;
                 }
-                if (id != caps->nullid) {
+                if (id != MT_ID_NULL) {
                         slot = firstbit(unused);
                         push_slot_changes(state, &data[i], prop[i], slot, syn);
                         SETBIT(used, slot);
@@ -304,7 +304,7 @@ static void apply_typeA_changes(struct mtdev_state *state,
         foreach_bit(slot, state->used & ~used) {
                 struct mtdev_slot tdata = state->data[slot];
                 bitmask_t tprop = BITMASK(MTDEV_TRACKING_ID);
-                tdata.abs[MTDEV_TRACKING_ID] = caps->nullid;
+                tdata.abs[MTDEV_TRACKING_ID] = MT_ID_NULL;
                 push_slot_changes(state, &tdata, tprop, slot, syn);
         }
         state->used = used;
@@ -337,10 +337,13 @@ static void convert_A_to_B(struct mtdev_state *state,
 
 int mtdev_init(struct mtdev *dev)
 {
+        int i;
         memset(dev, 0, sizeof(struct mtdev));
         dev->state = calloc(1, sizeof(struct mtdev_state));
         if (!dev->state)
                 return -ENOMEM;
+        for (i = 0; i < DIM_FINGER; i++)
+                dev->state->data[i].abs[MTDEV_TRACKING_ID] = MT_ID_NULL;
         return 0;
 }