evdev: use a different filter for low resolution touchpad on the Lenovo X230

[platform/upstream/libinput.git] / src / filter.c

diff --git a/src/filter.c b/src/filter.c
index 962d74d..b953bee 100644 (file)
--- a/src/filter.c
+++ b/src/filter.c
@@ -345,3 +345,40 @@ touchpad_accel_profile_linear(struct motion_filter *filter,
 
        return speed_out * TP_MAGIC_SLOWDOWN;
 }
+
+double
+touchpad_lenovo_x230_accel_profile(struct motion_filter *filter,
+                                     void *data,
+                                     double speed_in,
+                                     uint64_t time)
+{
+       /* Keep the magic factor from touchpad_accel_profile_linear.  */
+       const double TP_MAGIC_SLOWDOWN = 0.4;
+
+       /* Those touchpads presents an actual lower resolution that what is
+        * advertised. We see some jumps from the cursor due to the big steps
+        * in X and Y when we are receiving data.
+        * Apply a factor to minimize those jumps at low speed, and try
+        * keeping the same feeling as regular touchpads at high speed.
+        * It still feels slower but it is usable at least */
+       const double TP_MAGIC_LOW_RES_FACTOR = 4.0;
+       double speed_out;
+       struct pointer_accelerator *accel_filter =
+               (struct pointer_accelerator *)filter;
+
+       double s1, s2;
+       const double max_accel = accel_filter->accel *
+                                 TP_MAGIC_LOW_RES_FACTOR; /* unitless factor */
+       const double threshold = accel_filter->threshold /
+                                 TP_MAGIC_LOW_RES_FACTOR; /* units/ms */
+       const double incline = accel_filter->incline * TP_MAGIC_LOW_RES_FACTOR;
+
+       speed_in *= TP_MAGIC_SLOWDOWN / TP_MAGIC_LOW_RES_FACTOR;
+
+       s1 = min(1, speed_in * 5);
+       s2 = 1 + (speed_in - threshold) * incline;
+
+       speed_out = min(max_accel, s2 > 1 ? s2 : s1);
+
+       return speed_out * TP_MAGIC_SLOWDOWN / TP_MAGIC_LOW_RES_FACTOR;
+}