[RFC v2 libinput 2/2] buttonset: implement buttonset handling for Wacom tablet pads

[Jason Gerecke]

Did some practical testing of these patches and noticed two issues with 
the touchstrips:

On 3/17/2015 11:58 PM, Peter Hutterer wrote:
> From: Benjamin Tissoires <benjamin.tissoires at gmail.com>
>
> Same approach as evdev-tablet (started as copy/paste), with axis and buttons
> adjusted. Wacom's handling of pad devices requires a lot of non-obvious
> handling, e.g. ABS_THROTTLE is the second ring, ABS_RX is the strip, etc.
>
> This is not generic buttonset code, if we start supporting other devices for
> buttonsets we'll factor out a couple of the functions.
>
> The wheel and strip events are a bit of a problem: Wacom sends a 0 event on the
> axis when the finger is released. We can detect this if there is an ABS_MISC 0
> present in the same event and suppress it.  Won't work if any finger is down
> on any other wheel, strip or button but that's a kernel bug we'll fix once we
> figure out how.
>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires at redhat.com>
> Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
> ---
>   src/Makefile.am             |   2 +
>   src/evdev-buttonset-wacom.c | 533 ++++++++++++++++++++++++++++++++++++++++++++
>   src/evdev-buttonset-wacom.h |  63 ++++++
>   src/evdev.c                 |  18 +-
>   src/evdev.h                 |   3 +
>   src/libinput-private.h      |  16 ++
>   src/libinput.c              |  65 ++++++
>   7 files changed, 691 insertions(+), 9 deletions(-)
>   create mode 100644 src/evdev-buttonset-wacom.c
>   create mode 100644 src/evdev-buttonset-wacom.h
>
> [...]
 >
> +static inline double
> +normalize_strip(const struct input_absinfo *absinfo)
> +{
> +	/* strip axes don't use a proper value, they just shift the bit left
> +	 * for each position. 0 isn't a real value either, it's only sent on
> +	 * finger release */
> +	double min = 1,

Min should be set to 0 (i.e., log2(1)) here.

> +	       max = log2(absinfo->maximum);
> +	double range = max - min;
> +	double value = (log2(absinfo->value) - min) / range;
> +
> +	return value;
> +}
> +
> +/* Detect ring wraparound, current and old are normalized to [0, 1[ */
> +static inline double
> +guess_ring_delta(double current, double old)
> +{
> +	double d1, d2, d3;
> +
> +	d1 = current - old;
> +	d2 = (current + 1) - old;
> +	d3 = current - (old + 1);
> +
> +	if (fabs(d2) < fabs(d1))
> +		d1 = d2;
> +
> +	if (fabs(d3) < fabs(d1))
> +		d1 = d3;
> +
> +	return d1;
> +}
> +
> +static void
> +buttonset_check_notify_axes(struct buttonset_dispatch *buttonset,
> +			    struct evdev_device *device,
> +			    uint32_t time)
> +{
> +	struct libinput_device *base = &device->base;
> +	bool axis_update_needed = false;
> +	double deltas[LIBINPUT_BUTTONSET_MAX_NUM_AXES] = {0};
> +	double deltas_discrete[LIBINPUT_BUTTONSET_MAX_NUM_AXES] = {0};
> +	unsigned int a;
> +	unsigned int code;
> +
> +	for (a = 0; a <= buttonset->naxes; a++) {
> +		const struct input_absinfo *absinfo;
> +
> +		if (!bit_is_set(buttonset->changed_axes, a))
> +			continue;
> +
> +		code = buttonset->axis_map[a];
> +		assert(code != 0);
> +		absinfo = libevdev_get_abs_info(device->evdev, code);
> +		assert(absinfo);
> +
> +		switch (buttonset->types[a]) {
> +		case LIBINPUT_BUTTONSET_AXIS_RING:
> +			buttonset->axes[a] = normalize_ring(absinfo);
> +			deltas[a] = guess_ring_delta(buttonset->axes[a],
> +						     buttonset->axes_prev[a]);
> +			deltas_discrete[a] = unnormalize_ring_value(absinfo,
> +								    deltas[a]);
> +			break;
> +		case LIBINPUT_BUTTONSET_AXIS_STRIP:
> +			buttonset->axes[a] = normalize_strip(absinfo);
> +			deltas[a] = buttonset->axes[a] - buttonset->axes_prev[a];
> +			break;

When a touch goes up, normalize_strip will return a normalized value of 
negative infinity. You should add suppression logic like for the 
ABS_MISC case since it isn't a real value.

> +		default:
> +			log_bug_libinput(device->base.seat->libinput,
> +					 "Invalid axis update: %u\n", a);
> +			break;
> +		}
> +
> +		if (buttonset->have_abs_misc_terminator) {
> +			/* Suppress the reset to 0 on finger up. See the
> +			   comment in buttonset_process_absolute */
> +			if (libevdev_get_event_value(device->evdev,
> +						     EV_ABS,
> +						     ABS_MISC) == 0) {
> +				clear_bit(buttonset->changed_axes, a);
> +				buttonset->axes[a] = buttonset->axes_prev[a];
> +				continue;
> +			/* on finger down, reset the delta to 0 */
> +			} else {
> +				deltas[a] = 0;
> +				deltas_discrete[a] = 0;
> +			}
> +		}
> +
> +		axis_update_needed = true;
> +	}
> +
> +	if (axis_update_needed)
> +		buttonset_notify_axis(base,
> +				      time,
> +				      LIBINPUT_BUTTONSET_AXIS_SOURCE_UNKNOWN,
> +				      buttonset->changed_axes,
> +				      buttonset->axes,
> +				      deltas,
> +				      deltas_discrete);
> +
> +	memset(buttonset->changed_axes, 0, sizeof(buttonset->changed_axes));
> +	memcpy(buttonset->axes_prev,
> +	       buttonset->axes,
> +	       sizeof(buttonset->axes_prev));
> +	buttonset->have_abs_misc_terminator = false;
> +}
> +
> [...]
>

-- 
Jason
---
Now instead of four in the eights place /
you’ve got three, ‘Cause you added one /
(That is to say, eight) to the two, /
But you can’t take seven from three, /
So you look at the sixty-fours....