Attachment 137524 Details for Bug 105108 – 0001-evdev-change-hysteresis-to-work-across-both-axes.patch

[patch] 0001-evdev-change-hysteresis-to-work-across-both-axes.patch

0001-evdev-change-hysteresis-to-work-across-both-axes.patch (text/plain), 5.55 KB, created by Peter Hutterer on 2018-02-22 06:50:41 UTC

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Creator: Peter Hutterer

Created: 2018-02-22 06:50:41 UTC

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patch

obsolete

>From 4fa668d94bf060fe37186efa662c80d682d7282e Mon Sep 17 00:00:00 2001
>From: Peter Hutterer <peter.hutterer@who-t.net>
>Date: Wed, 1 Feb 2017 12:24:37 +1000
>Subject: [PATCH libinput] evdev: change hysteresis to work across both axes
>MIME-Version: 1.0
>Content-Type: text/plain; charset=UTF-8
>Content-Transfer-Encoding: 8bit
>
>The previous approach causes axis snapping, preventing things like drawing a
>circle, see e.g. https://bugs.freedesktop.org/show_bug.cgi?id=99410
>
>Switch to a different approach that at least looks at both axes at the same
>time. If one axis is outside of the margin take the other axis as-is and don't
>apply hysteresis to it. This prevents axis snapping but exposes another bug:
>there is a 'margin'-sized zone where we can get cursor jumps.
>
>Assume a vector of x/y with x larger than the margin, the value y can take:
>* y for [0, margin)
>* y-margin for [margin, â)
>Thus y increases towards margin, then jumps back to 0 when it hits margin.
>Then in increases linearly from there on.
>
>The only way around this is calculating the exact vector, but that requires a
>lot of expensive calculations.
>
>It's unclear whether this change is perceptible as the actual movement is
>miniscule and the upside is that we don't have axis snapping anymore, so
>there's a small win. You're allowed a very small bottle of champagne. Don't
>pop it too loud.
>
>Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
>---
> src/evdev-fallback.c    | 11 ++++-------
> src/evdev-mt-touchpad.c | 19 +++++++------------
> src/evdev.h             | 50 ++++++++++++++++++++++++++++++++++++++-----------
> 3 files changed, 50 insertions(+), 30 deletions(-)
>
>diff --git a/src/evdev-fallback.c b/src/evdev-fallback.c
>index 13e130ac..f5b00cec 100644
>--- a/src/evdev-fallback.c
>+++ b/src/evdev-fallback.c
>@@ -243,14 +243,11 @@ fallback_filter_defuzz_touch(struct fallback_dispatch *dispatch,
> 	if (!dispatch->mt.want_hysteresis)
> 		return false;
> 
>-	point.x = evdev_hysteresis(slot->point.x,
>-				   slot->hysteresis_center.x,
>-				   dispatch->mt.hysteresis_margin.x);
>-	point.y = evdev_hysteresis(slot->point.y,
>-				   slot->hysteresis_center.y,
>-				   dispatch->mt.hysteresis_margin.y);
>+	point = evdev_hysteresis(slot->point,
>+				 slot->hysteresis_center,
>+				 dispatch->mt.hysteresis_margin);
> 
>-	slot->hysteresis_center = slot->point;
>+	slot->hysteresis_center = point;
> 	if (point.x == slot->point.x && point.y == slot->point.y)
> 		return true;
> 
>diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
>index 8bb0661b..aeb91a71 100644
>--- a/src/evdev-mt-touchpad.c
>+++ b/src/evdev-mt-touchpad.c
>@@ -135,22 +135,17 @@ static inline void
> tp_motion_hysteresis(struct tp_dispatch *tp,
> 		     struct tp_touch *t)
> {
>-	int x = t->point.x,
>-	    y = t->point.y;
>+	struct device_coords p;
> 
> 	if (t->history.count == 0) {
> 		t->hysteresis_center = t->point;
> 	} else {
>-		x = evdev_hysteresis(x,
>-				     t->hysteresis_center.x,
>-				     tp->hysteresis_margin.x);
>-		y = evdev_hysteresis(y,
>-				     t->hysteresis_center.y,
>-				     tp->hysteresis_margin.y);
>-		t->hysteresis_center.x = x;
>-		t->hysteresis_center.y = y;
>-		t->point.x = x;
>-		t->point.y = y;
>+
>+		p = evdev_hysteresis(t->point,
>+				     t->hysteresis_center,
>+				     tp->hysteresis_margin);
>+		t->hysteresis_center = p;
>+		t->point = p;
> 	}
> }
> 
>diff --git a/src/evdev.h b/src/evdev.h
>index 4c42f6eb..185d8bff 100644
>--- a/src/evdev.h
>+++ b/src/evdev.h
>@@ -605,10 +605,18 @@ evdev_to_left_handed(struct evdev_device *device,
>  * Otherwise, the center has a dead zone of size margin around it and the
>  * first reachable point is the margin edge.
>  *
>- * Hysteresis is handled separately per axis (and the window is thus
>- * rectangular, not circular). It is unkown if that's an issue, but the
>- * calculation to do circular hysteresis are nontrivial, especially since
>- * many touchpads have uneven x/y resolutions.
>+ * If either x or y is outside the margin, then no hysteresis is applied for
>+ * the other axis and that value is taken as is. Thus, the four return
>+ * values for a vector (x, y) are:
>+ * 1) (center.x, center.y)     if x/y are within margin
>+ * 2) (x - margin, y - margin) if x/y are outside margin
>+ * 1) (x - margin, y)          if x is outside margin, y inside
>+ * 1) (x, y - margin)          if y is outside margin, x inside
>+ *
>+ * This falsifies pointer motion slightly but the hysteresis is small enough
>+ * to make this a nonissue. The calculations to do correct circular
>+ * hysteresis are nontrivial, especially since many touchpads have uneven
>+ * x/y resolutions.
>  *
>  * @param in The input coordinate
>  * @param center Current center of the hysteresis
>@@ -616,17 +624,37 @@ evdev_to_left_handed(struct evdev_device *device,
>  *
>  * @return The new center of the hysteresis
>  */
>-static inline int
>-evdev_hysteresis(int in, int center, int margin)
>+
>+static inline struct device_coords
>+evdev_hysteresis(const struct device_coords point,
>+		 const struct device_coords center,
>+		 const struct device_coords margin)
> {
>-	int diff = in - center;
>-	if (abs(diff) <= margin)
>+	struct device_coords diff;
>+	struct device_coords p;
>+
>+	diff.x = point.x - center.x;
>+	diff.y = point.y - center.y;
>+
>+	if (abs(diff.x) <= margin.x &&
>+	    abs(diff.y) <= margin.y)
> 		return center;
> 
>-	if (diff > 0)
>-		return in - margin;
>+	if (diff.x > margin.x)
>+		p.x = point.x - margin.x;
>+	else if (diff.x < -margin.x)
>+		p.x = point.x + margin.x;
> 	else
>-		return in + margin;
>+		p.x = point.x;
>+
>+	if (diff.y > margin.y)
>+		p.y = point.y - margin.y;
>+	else if (diff.y < -margin.y)
>+		p.y = point.y + margin.y;
>+	else
>+		p.y = point.y;
>+
>+	return p;
> }
> 
> static inline struct libinput *
>-- 
>2.14.3
>

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