3 files changed, 31 insertions, 0 deletions

diff --git a/src/capabilities.c b/src/capabilities.c
index 7316f01..620ab60 100644
--- a/src/capabilities.c
+++ b/src/capabilities.c
@@ -26,6 +26,8 @@
 
 #define ADDCAP(s, c, x) strcat(s, c->has_##x ? " " #x : "")
 
+static const int SN_COORD = 250;        /* coordinate signal-to-noise ratio */
+
 static const int bits_per_long = 8 * sizeof(long);
 
 static inline int nlongs(int nbit)
@@ -78,6 +80,13 @@ int read_capabilities(struct Capabilities *cap, int fd)
 
         cap->has_mtdata = cap->has_position_x && cap->has_position_y;
 
+        cap->xfuzz = cap->abs_position_x.fuzz;
+        cap->yfuzz = cap->abs_position_y.fuzz;
+        if (cap->xfuzz <= 0 || cap->yfuzz <= 0) {
+                cap->xfuzz = get_cap_xsize(cap) / SN_COORD;
+                cap->yfuzz = get_cap_ysize(cap) / SN_COORD;
+        }
+
         return 0;
 }
 
diff --git a/src/capabilities.h b/src/capabilities.h
index dc257ce..591eed6 100644
--- a/src/capabilities.h
+++ b/src/capabilities.h
@@ -38,6 +38,7 @@ struct Capabilities {
         struct input_absinfo abs_orientation;
         struct input_absinfo abs_position_x;
         struct input_absinfo abs_position_y;
+        int xfuzz, yfuzz;
 };
 
 int read_capabilities(struct Capabilities *cap, int fd);
diff --git a/src/hwstate.c b/src/hwstate.c
index 40cef5b..4af636c 100644
--- a/src/hwstate.c
+++ b/src/hwstate.c
@@ -44,16 +44,37 @@ inline int dist2(const struct FingerData *a, const struct FingerData *b)
         return dx * dx + dy * dy;
 }
 
+/* Dmitry Torokhov's code from kernel/driver/input/input.c */
+static int defuzz(int value, int old_val, int fuzz)
+{
+        if (fuzz) {
+                if (value > old_val - fuzz / 2 && value < old_val + fuzz / 2)
+                        return old_val;
+
+                if (value > old_val - fuzz && value < old_val + fuzz)
+                        return (old_val * 3 + value) / 4;
+
+                if (value > old_val - fuzz * 2 && value < old_val + fuzz * 2)
+                        return (old_val + value) / 2;
+        }
+
+        return value;
+}
+
 static void set_finger(struct FingerState *fs,
                        const struct FingerData *hw, int id,
                        const struct Capabilities *caps)
 {
+        int x = defuzz(hw->position_x, fs->hw.position_x, caps->xfuzz);
+        int y = defuzz(hw->position_y, fs->hw.position_y, caps->yfuzz);
         fs->hw = *hw;
         fs->id = id;
         if (!caps->has_touch_minor)
                 fs->hw.touch_minor = hw->touch_major;
         if (!caps->has_width_minor)
                 fs->hw.width_minor = hw->width_major;
+        fs->hw.position_x = x;
+        fs->hw.position_y = y;
 }
 
 void modify_hwstate(struct HWState *s,