[PATCH xf86-input-synaptics] Always count tripletap + click as 3 fingerclick on pads with < 3 touches

[Hans de Goede]

When trying to do a 3 fingerclick on a touchpad which only tracks 2 touches,
this may register as a 3 or 2 fingerclick depending on the order in which
the touchpad detects the fingers. If the 2 outer fingers of the 3 get seen
first, then the 2 touches will be too far apart for the heuristic to see
them as being close together, and the click gets counted as a 2 finger click.

A user will likely never do a 2 finger click with a 3th finger resting
somewhere else on the pad, where-as the above misdetection of the clicks is
a real issue, so simply always count a click with trippletap set as a
3 finger click on pads which track less then 3 touches.

https://bugzilla.redhat.com/show_bug.cgi?id=1086218

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 src/synaptics.c | 25 +++++--------------------
 1 file changed, 5 insertions(+), 20 deletions(-)

diff --git a/src/synaptics.c b/src/synaptics.c
index f4c1d4a..118d1c6 100644
--- a/src/synaptics.c
+++ b/src/synaptics.c
@@ -2673,26 +2673,11 @@ clickpad_guess_clickfingers(SynapticsPrivate * priv,
     }
 
     /* Some trackpads touchpad only track two touchpoints but announce
-       BTN_TOOL_TRIPLETAP (which sets hw->numFingers to 3).
-       This can affect clickfingers, in the following ways:
-       * one finger down: normal click
-       * two fingers down, close together: 2 finger click
-       * two fingers down, apart: normal click
-       * three fingers down, close together: 3 finger click
-       * three fingers down, with two grouped next to each other: should be
-       * 2-finger click but we can't detect this.
-       * so: if two detected fingers are close together and HW says three
-       * fingers, make it three fingers.
-       * if two detected fingers are apart and HW says three fingers, make
-       * it a two-finger click, guessing that the third finger is somewhere
-       * close to another finger.
-       */
-    if (hw->numFingers >= 3 && nfingers < hw->numFingers) {
-        if (!nfingers) /* touchpoints too far apart */
-            nfingers = 2;
-        else
-            nfingers++;
-    }
+     * BTN_TOOL_TRIPLETAP (which sets hw->numFingers to 3), when this happens
+     * the user likely intents to do a 3 finger click, so handle it as such.
+     */
+    if (hw->numFingers >= 3 && hw->num_mt_mask < 3)
+        nfingers = 3;
 
     return nfingers;
 }
-- 
1.9.0