2 files changed, 27 insertions, 1 deletions

diff --git a/src/mtstate.c b/src/mtstate.c
index c3bcc78..1e2eeef 100644
--- a/src/mtstate.c
+++ b/src/mtstate.c
@@ -24,6 +24,11 @@
 #define TOUCH_WIDTH(hw) (0.05 * hw->width_major)
 #define TOUCH_SCALE(caps) (0.05 * caps->abs_touch_major.maximum)
 
+#define THUMB_TOUCH(hw) (1.2 * hw->touch_minor)
+#define THUMB_WIDTH_TOUCH(hw) (3 * hw->touch_major)
+#define THUMB_WIDTH_WIDTH(hw) (1.2 * hw->width_minor)
+#define THUMB_WIDTH_SIZE(hw, caps) (0.15 * get_cap_xsize(caps))
+
 void init_mtstate(struct MTState *s)
 {
         memset(s, 0, sizeof(struct MTState));
@@ -39,12 +44,33 @@ static int touching_finger(const struct FingerData *hw,
         return 1;
 }
 
+/*
+ * Thumb detection:
+ *
+ * The thumb is large and oval, even when not pressed hard against the
+ * surface. The width_major parameter is therefore bounded from below
+ * by all three values touch_major, width_minor, and trackpad size.
+ *
+ */
+static int thumb_finger(const struct FingerData *hw,
+                        const struct Capabilities *caps)
+{
+        if (!caps->has_touch_major || !caps->has_touch_minor ||
+            !caps->has_width_major || !caps->has_width_minor)
+                return 0;
+        return  hw->touch_major > THUMB_TOUCH(hw) &&
+                hw->width_major > THUMB_WIDTH_TOUCH(hw) &&
+                hw->width_major > THUMB_WIDTH_WIDTH(hw) &&
+                hw->width_major > THUMB_WIDTH_SIZE(hw, caps);
+}
+
 static int set_finger(struct MTFinger *f,
                       const struct FingerState *fs,
                       const struct Capabilities *caps)
 {
         f->hw = fs->hw;
         f->id = fs->id;
+        f->thumb = thumb_finger(&fs->hw, caps);
 }
 
 void extract_mtstate(struct MTState *s,
diff --git a/src/mtstate.h b/src/mtstate.h
index a8feaa4..ac0b18d 100644
--- a/src/mtstate.h
+++ b/src/mtstate.h
@@ -26,7 +26,7 @@
 
 struct MTFinger {
         struct FingerData hw;
-        int id;
+        int id, thumb;
 };
 
 struct MTState {