[PATCH xf86-input-synaptics 8/8] Wait for *new* coordinates on a clickpad click before reporting the click

[Hans de Goede]

It is possible for a click to get reported before any related touch events
get reported, here is the relevant part of an evemu-record session on a T440s:

E: 3.985585 0000 0000 0000	# ------------ SYN_REPORT (0) ----------
E: 3.997419 0003 0039 -001	# EV_ABS / ABS_MT_TRACKING_ID   -1
E: 3.997419 0001 014a 0000	# EV_KEY / BTN_TOUCH            0
E: 3.997419 0003 0018 0000	# EV_ABS / ABS_PRESSURE         0
E: 3.997419 0001 0145 0000	# EV_KEY / BTN_TOOL_FINGER      0
E: 3.997419 0000 0000 0000	# ------------ SYN_REPORT (0) ----------
E: 5.117881 0001 0110 0001	# EV_KEY / BTN_LEFT             1
E: 5.117881 0000 0000 0000	# ------------ SYN_REPORT (0) ----------
E: 5.133422 0003 0039 0187	# EV_ABS / ABS_MT_TRACKING_ID   187
E: 5.133422 0003 0035 3098	# EV_ABS / ABS_MT_POSITION_X    3098
E: 5.133422 0003 0036 3282	# EV_ABS / ABS_MT_POSITION_Y    3282
E: 5.133422 0003 003a 0046	# EV_ABS / ABS_MT_PRESSURE      46
E: 5.133422 0001 014a 0001	# EV_KEY / BTN_TOUCH            1
E: 5.133422 0003 0000 3102	# EV_ABS / ABS_X                3102
E: 5.133422 0003 0001 3282	# EV_ABS / ABS_Y                3282
E: 5.133422 0003 0018 0046	# EV_ABS / ABS_PRESSURE         46
E: 5.133422 0001 0145 0001	# EV_KEY / BTN_TOOL_FINGER      1
E: 5.133422 0000 0000 0000	# ------------ SYN_REPORT (0) ----------

Notice the BTN_LEFT event all by itself!

If this happens, it may lead to the following problem scenario:
-touch the touchpad in its right click area
-let go of the touchpad
-rapidly click in the middle area, so that BTN_LEFT gets reported before the
 new coordinates (such as seen in the trace above, this may require some
 practicing with evemu-record to reproduce)
-the driver registers the click as a right click because it uses the
 old coordinates from the cumulative coordinates to determine the
 click location

This commit fixes this by:
1) Resetting the cumulative coordinates not only when no button is pressed,
   but also when there is no finger touching the touchpad, so that when
   we do get a touch the cumulative coordinates start at the right place
2) Delaying processing the BTN_LEFT down transition if there is no finger
   touching the touchpad

This approach has one downside, if we wrongly identify a touchpad as
a clickpad, then the left button won't work unless the user touches the
touchpad while clicking the left button.

If we want we can fix this by doing something like this:
1) Making update_hw_button_state return a delay; and
2) Tracking that we've delayed BTN_LEFT down transition processing; and
3) When we've delayed BTN_LEFT down transition return a small delay value; and
4) If when we're called again we still don't have a finger down, just
   treat the click as a BTN_LEFT

But this is not worth the trouble IMHO, the proper thing to do in this
scenario is to fix the mis-identification of the touchpad as a clickpad.

Signed-off-by: Hans de Goede <hdegoede at redhat.com>
---
 src/eventcomm.c | 5 +++--
 src/synaptics.c | 7 +++++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/eventcomm.c b/src/eventcomm.c
index fe57aa8..231afbc 100644
--- a/src/eventcomm.c
+++ b/src/eventcomm.c
@@ -675,8 +675,9 @@ EventReadHwState(InputInfoPtr pInfo,
 
     SynapticsResetTouchHwState(hw, FALSE);
 
-    /* Reset cumulative values if buttons were not previously pressed */
-    if (!hw->left && !hw->right && !hw->middle) {
+    /* Reset cumulative values if buttons were not previously pressed,
+     * or no finger was previously present. */
+    if ((!hw->left && !hw->right && !hw->middle) || hw->z < para->finger_low) {
         hw->cumulative_dx = hw->x;
         hw->cumulative_dy = hw->y;
         sync_cumulative = TRUE;
diff --git a/src/synaptics.c b/src/synaptics.c
index bd14100..59fcf48 100644
--- a/src/synaptics.c
+++ b/src/synaptics.c
@@ -2810,6 +2810,12 @@ update_hw_button_state(const InputInfoPtr pInfo, struct SynapticsHwState *hw,
     if (para->clickpad) {
         /* hw->left is down, but no other buttons were already down */
         if (!(priv->lastButtons & 7) && hw->left && !hw->right && !hw->middle) {
+            /* If the finger down event is delayed, the x and y
+             * coordinates are stale so we delay processing the click */
+            if (hw->z < para->finger_low) {
+                hw->left = 0;
+                goto out;
+            }
             if (is_inside_rightbutton_area(para, hw->x, hw->y)) {
                 hw->left = 0;
                 hw->right = 1;
@@ -2841,6 +2847,7 @@ update_hw_button_state(const InputInfoPtr pInfo, struct SynapticsHwState *hw,
     if (hw->left && !(priv->lastButtons & 7) && hw->numFingers >= 1)
         handle_clickfinger(priv, hw);
 
+out:
     /* Two finger emulation */
     if (hw->numFingers == 1 && hw->z >= para->emulate_twofinger_z &&
         hw->fingerWidth >= para->emulate_twofinger_w) {
-- 
1.9.0