[PATCH libinput] filter: fix constant acceleration for the X230

[Hans de Goede]

Hi,

On 31-08-15 06:16, Peter Hutterer wrote:
> The x230 has a special acceleration method that relies on the touchpad magic
> slowdown. This was missing from commit c8da19b50a30d8, making two-finger
> scroll motions unusably fast
>
> https://bugs.freedesktop.org/show_bug.cgi?id=91819
>
> Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>

LGTM: Reviewed-by: Hans de Goede <hdegoede at redhat.com>

Regards,

Hans

> ---
>   src/filter.c | 33 +++++++++++++++++++++++----------
>   1 file changed, 23 insertions(+), 10 deletions(-)
>
> diff --git a/src/filter.c b/src/filter.c
> index 5df50d3..a646857 100644
> --- a/src/filter.c
> +++ b/src/filter.c
> @@ -114,6 +114,8 @@ filter_get_speed(struct motion_filter *filter)
>   #define X230_THRESHOLD v_ms2us(0.4)		/* in units/us */
>   #define X230_ACCELERATION 2.0			/* unitless factor */
>   #define X230_INCLINE 1.1			/* unitless factor */
> +#define X230_MAGIC_SLOWDOWN 0.4			/* unitless */
> +#define X230_TP_MAGIC_LOW_RES_FACTOR 4.0	/* unitless */
>
>   /*
>    * Pointer acceleration filter constants
> @@ -421,6 +423,21 @@ accelerator_filter_x230(struct motion_filter *filter,
>   }
>
>   static struct normalized_coords
> +accelerator_filter_constant_x230(struct motion_filter *filter,
> +				 const struct normalized_coords *unaccelerated,
> +				 void *data, uint64_t time)
> +{
> +	struct normalized_coords normalized;
> +	const double factor =
> +		X230_MAGIC_SLOWDOWN/X230_TP_MAGIC_LOW_RES_FACTOR;
> +
> +	normalized.x = factor * unaccelerated->x;
> +	normalized.y = factor * unaccelerated->y;
> +
> +	return normalized;
> +}
> +
> +static struct normalized_coords
>   touchpad_constant_filter(struct motion_filter *filter,
>   			 const struct normalized_coords *unaccelerated,
>   			 void *data, uint64_t time)
> @@ -631,26 +648,22 @@ touchpad_lenovo_x230_accel_profile(struct motion_filter *filter,
>   				      double speed_in,
>   				      uint64_t time)
>   {
> -	/* Keep the magic factor from touchpad_accel_profile_linear.  */
> -	const double X230_MAGIC_SLOWDOWN = 0.4; /* unitless */
> -
>   	/* 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; /* unitless */
>   	double factor; /* unitless */
>   	struct pointer_accelerator *accel_filter =
>   		(struct pointer_accelerator *)filter;
>
>   	double f1, f2; /* unitless */
>   	const double max_accel = accel_filter->accel *
> -				  TP_MAGIC_LOW_RES_FACTOR; /* unitless factor */
> +				  X230_TP_MAGIC_LOW_RES_FACTOR; /* unitless factor */
>   	const double threshold = accel_filter->threshold /
> -				  TP_MAGIC_LOW_RES_FACTOR; /* units/us */
> -	const double incline = accel_filter->incline * TP_MAGIC_LOW_RES_FACTOR;
> +				  X230_TP_MAGIC_LOW_RES_FACTOR; /* units/us */
> +	const double incline = accel_filter->incline * X230_TP_MAGIC_LOW_RES_FACTOR;
>
>   	/* Note: the magic values in this function are obtained by
>   	 * trial-and-error. No other meaning should be interpreted.
> @@ -658,14 +671,14 @@ touchpad_lenovo_x230_accel_profile(struct motion_filter *filter,
>   	 * pointer_accel_profile_linear(), look at the git history of that
>   	 * function for an explaination of what the min/max/etc. does.
>   	 */
> -	speed_in *= X230_MAGIC_SLOWDOWN / TP_MAGIC_LOW_RES_FACTOR;
> +	speed_in *= X230_MAGIC_SLOWDOWN / X230_TP_MAGIC_LOW_RES_FACTOR;
>
>   	f1 = min(1, v_us2ms(speed_in) * 5);
>   	f2 = 1 + (v_us2ms(speed_in) - v_us2ms(threshold)) * incline;
>
>   	factor = min(max_accel, f2 > 1 ? f2 : f1);
>
> -	return factor * X230_MAGIC_SLOWDOWN / TP_MAGIC_LOW_RES_FACTOR;
> +	return factor * X230_MAGIC_SLOWDOWN / X230_TP_MAGIC_LOW_RES_FACTOR;
>   }
>
>   double
> @@ -795,7 +808,7 @@ create_pointer_accelerator_filter_touchpad(int dpi)
>
>   struct motion_filter_interface accelerator_interface_x230 = {
>   	.filter = accelerator_filter_x230,
> -	.filter_constant = accelerator_filter_noop,
> +	.filter_constant = accelerator_filter_constant_x230,
>   	.restart = accelerator_restart,
>   	.destroy = accelerator_destroy,
>   	.set_speed = accelerator_set_speed,
>