[PATCH libinput] Add pressure calculation for TOUCH/WIDTH touchpads

[Peter Hutterer]

On Sat, Aug 15, 2015 at 03:51:57PM +0200, Ming-ting Yao Wei wrote:
> This patch is a simple ellipsis size thumb detection. By using MAJOR*MINOR we
> can get what correspond to the pressure value, and we can find a suitable
> pressure threshold that can separate thumbs from fingers.
> 
> Signed-off-by: Yao Wei <mwei at lxde.org>
> 
> ---
>  src/evdev-mt-touchpad.c | 39 ++++++++++++++++++++++++++++++++++++++-
>  src/evdev-mt-touchpad.h |  7 +++++++
>  2 files changed, 45 insertions(+), 1 deletion(-)
> 
> diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
> index 872da98..2096dee 100644
> --- a/src/evdev-mt-touchpad.c
> +++ b/src/evdev-mt-touchpad.c
> @@ -319,6 +319,14 @@ tp_process_absolute(struct tp_dispatch *tp,
>  		t->dirty = true;
>  		tp->queued |= TOUCHPAD_EVENT_MOTION;
>  		break;
> +	case ABS_MT_TOUCH_MAJOR:
> +		t->ellipsis.major = e->value;
> +		/* falls through, minor = major when major changes */

no, you're not guaranteed to get a ABS_MT_TOUCH_MINOR, e.g. if the value
doesn't change. when that happens, you'd now be overwriting the minor value
with the wrong one.

> +	case ABS_MT_TOUCH_MINOR:
> +		t->ellipsis.minor = e->value;
> +		t->dirty = true;
> +		tp->queued |= TOUCHPAD_EVENT_MOTION;
> +		break;
>  	}
>  }
>  
> @@ -697,8 +705,18 @@ tp_thumb_detect(struct tp_dispatch *tp, struct tp_touch *t, uint64_t time)
>  	 * A finger that remains at the very bottom of the touchpad becomes
>  	 * a thumb.
>  	 */
> -	if (t->pressure > tp->thumb.threshold)
> +	if (tp->thumb.pressure_detection && t->pressure > tp->thumb.threshold)
>  		t->thumb.state = THUMB_STATE_YES;
> +	else if (tp->thumb.ellipsis_detection) {
> +		log_debug(tp_libinput_context(tp),
> +			  "ellipsis: major %d, minor %d => %d, threshold is %d\n",
> +			  t->ellipsis.major,
> +			  t->ellipsis.minor,
> +			  t->ellipsis.major * t->ellipsis.minor,
> +			  tp->thumb.threshold);

please remove such messages before patch submission. 

> +		if (t->ellipsis.major * t->ellipsis.minor > tp->thumb.threshold)
> +			t->thumb.state = THUMB_STATE_YES;
> +	}
>  	else if (t->point.y > tp->thumb.lower_thumb_line &&
>  		 tp->scroll.method != LIBINPUT_CONFIG_SCROLL_EDGE &&
>  		 t->thumb.first_touch_time + THUMB_MOVE_TIMEOUT < time)
> @@ -1783,6 +1801,25 @@ tp_init_thumb(struct tp_dispatch *tp)
>  	tp->thumb.upper_thumb_line = ymax - yres * 15;
>  	tp->thumb.lower_thumb_line = ymax - yres * 8;
>  
> +	abs = libevdev_get_abs_info(device->evdev, ABS_MT_TOUCH_MAJOR);
> +	if (!abs)
> +		goto pressure;
> +
> +	/* Use ABS_MT_TOUCH_MAJOR and ABS_MT_TOUCH_MINOR as pressure
> +	 * detection.
> +	 * Use MacBookPro11,1 (13" Retina, Mid-2014) as reference,
> +	 * The ABS_MT_TOUCH_MAJOR * ABS_MT_TOUCH_MINOR should not
> +	 * exceed 350000. However, this need a test if higher res
> +	 * touchpads exhibit higher threshold value */
> +
> +	tp->thumb.detect_thumbs = true;
> +	tp->thumb.ellipsis_detection = true;

if elipsis and thumb detection are exclusive, it'd be better to have a
"mode" field that is set to THUMB_MODE_NONE, THUMB_MODE_PRESSURE, etc. that
way you can dropi detect_thumbs too.

> +	tp->thumb.threshold = 350000.0;

I'd like some more explanation in how you arrived at 350000 please. it's a
pretty magic number, there should be some way of understanding why that
number and not something else.

> +
> +	goto out; /* skip pressure detection */

yikes. not the best use of goto, please use helper functions instead here.

Cheers,
   Peter

> +
> +pressure:
> +
>  	abs = libevdev_get_abs_info(device->evdev, ABS_MT_PRESSURE);
>  	if (!abs)
>  		goto out;
> diff --git a/src/evdev-mt-touchpad.h b/src/evdev-mt-touchpad.h
> index 3bd8425..110f824 100644
> --- a/src/evdev-mt-touchpad.h
> +++ b/src/evdev-mt-touchpad.h
> @@ -215,6 +215,11 @@ struct tp_touch {
>  		uint64_t first_touch_time;
>  		struct device_coords initial;
>  	} thumb;
> +
> +	struct {
> +		int major;
> +		int minor;
> +	} ellipsis;
>  };
>  
>  struct tp_dispatch {
> @@ -347,6 +352,8 @@ struct tp_dispatch {
>  
>  	struct {
>  		bool detect_thumbs;
> +		bool pressure_detection;
> +		bool ellipsis_detection;
>  		int threshold;
>  		int upper_thumb_line;
>  		int lower_thumb_line;
> -- 
> 2.5.0
>