Attachment 137715 Details for Bug 105306 – elliptical-hysteresis-v1.patch

[patch] elliptical-hysteresis-v1.patch

elliptical-hysteresis-v1.patch (text/plain), 6.86 KB, created by Daniel van Vugt on 2018-03-01 09:19:09 UTC

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Creator: Daniel van Vugt

Created: 2018-03-01 09:19:09 UTC

Size: 6.86 KB

patch

obsolete

>From 810caa82a6babffba3b30e4897c82e0df4843db4 Mon Sep 17 00:00:00 2001
>From: Daniel van Vugt <daniel.van.vugt@canonical.com>
>Date: Thu, 1 Mar 2018 17:03:28 +0800
>Subject: [PATCH] Introduce omnidirectional (elliptical) hysteresis
>
>This changes the hysteresis region to an ellipse (usually cirlce), where
>previously it was a rectangle (usually square).
>
>Using an ellipse means the algorithm is no longer more sensitive in some
>directions than others. It is now omnidirectional, which solves a few
>problems:
>  * Moving a finger in small circles now creates circles, not squares.
>  * Moving a finger in a curve no longer snaps the cursor to vertical
>    or horizontal lines. The cursor now follows a similar curve to the
>    finger.
>---
> src/evdev-fallback.c    |  9 ++---
> src/evdev-mt-touchpad.c | 23 ++++--------
> src/evdev.h             | 94 ++++++++++++++++++++++++++++++++-----------------
> 3 files changed, 71 insertions(+), 55 deletions(-)
>
>diff --git a/src/evdev-fallback.c b/src/evdev-fallback.c
>index 03f10a85..d1ca81f0 100644
>--- a/src/evdev-fallback.c
>+++ b/src/evdev-fallback.c
>@@ -127,12 +127,9 @@ 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;
> 	if (point.x == slot->point.x && point.y == slot->point.y)
>diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
>index 2a6cdcef..5f5c31c3 100644
>--- a/src/evdev-mt-touchpad.c
>+++ b/src/evdev-mt-touchpad.c
>@@ -155,26 +155,15 @@ static inline void
> tp_motion_hysteresis(struct tp_dispatch *tp,
> 		     struct tp_touch *t)
> {
>-	int x = t->point.x,
>-	    y = t->point.y;
>-
> 	if (!tp->hysteresis.enabled)
> 		return;
> 
>-	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;
>-	}
>+	if (t->history.count > 0)
>+		t->point = evdev_hysteresis(&t->point,
>+					    &t->hysteresis_center,
>+					    &tp->hysteresis.margin);
>+
>+	t->hysteresis_center = t->point;
> }
> 
> static inline void
>diff --git a/src/evdev.h b/src/evdev.h
>index 162adecb..7fc21690 100644
>--- a/src/evdev.h
>+++ b/src/evdev.h
>@@ -602,11 +602,11 @@ evdev_to_left_handed(struct evdev_device *device,
>  * Apply a hysteresis filtering to the coordinate in, based on the current
>  * hysteresis center and the margin. If 'in' is within 'margin' of center,
>  * return the center (and thus filter the motion). If 'in' is outside,
>- * return a point on the edge of the new margin. So for a point x in the
>- * space outside c + margin we return r:
>- * +---+       +---+
>+ * return a point on the edge of the new margin (which is an ellipse, usually
>+ * a circle). So for a point x in the space outside c + margin we return r:
>+ * ,---.       ,---.
>  * | c |  x â  | r x
>- * +---+       +---+
>+ * `---'       `---'
>  *
>  * The effect of this is that initial small motions are filtered. Once we
>  * move into one direction we lag the real coordinates by 'margin' but any
>@@ -619,41 +619,71 @@ 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.
>- *
>- * Given coordinates, 0, 1, 2, ... this is what we return for a margin of 3
>- * and a center of 0:
>- *
>- * Input:  1 2 3 4 5 6 5 4 3 2 1 0 -1
>- * Coord:  0 0 0 1 2 3 3 3 3 3 3 3 2
>- * Center: 0 0 0 1 2 3 3 3 3 3 3 3 2
>- *
>- * Problem: viewed from a stationary finger that starts moving, the
>- * hysteresis margin is M in both directions. Once we start moving
>- * continuously though, the margin is 0 in the movement direction and 2*M to
>- * change direction. That makes the finger less responsive to directional
>- * changes than to the original movement.
>- *
>  * @param in The input coordinate
>  * @param center Current center of the hysteresis
>  * @param margin Hysteresis width (on each side)
>  *
>  * @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 *in,
>+		 const struct device_coords *center,
>+		 const struct device_coords *margin)
> {
>-	int diff = in - center;
>-	if (abs(diff) <= margin)
>-		return center;
>-
>-	if (diff > 0)
>-		return in - margin;
>-	else
>-		return in + margin;
>+	int dx = in->x - center->x;
>+	int dy = in->y - center->y;
>+	int dx2 = dx * dx;
>+	int dy2 = dy * dy;
>+	int a = margin->x;
>+	int b = margin->y;
>+	double normalized_finger_distance, finger_distance, margin_distance;
>+	double lag_x, lag_y;
>+	struct device_coords result;
>+
>+	if (!a || !b)
>+		return *in;
>+
>+	/*
>+	 * Basic equation for an ellipse of radii a,b:
>+	 *   xÂ²/aÂ² + yÂ²/bÂ² = 1
>+	 * But we start by making a scaled ellipse passing through the
>+	 * relative finger location (dx,dy). So the scale of this ellipse is
>+	 * the ratio of finger_distance to margin_distance:
>+	 *   dxÂ²/aÂ² + dyÂ²/bÂ² = normalized_finger_distanceÂ²
>+	 */
>+	normalized_finger_distance = sqrt((double)dx2 / (a * a) +
>+					  (double)dy2 / (b * b));
>+
>+	/* Which means anything less than 1 is within the elliptical margin */
>+	if (normalized_finger_distance < 1.0)
>+		return *center;
>+
>+	finger_distance = sqrt(dx2 + dy2);
>+	margin_distance = finger_distance / normalized_finger_distance;
>+
>+	/*
>+	 * Now calculate the x,y coordinates on the edge of the margin ellipse
>+	 * where it intersects the finger vector. Shortcut: We achieve this by
>+	 * finding the point with the same gradient as dy/dx.
>+	 */
>+	if (dx) {
>+		double gradient = (double)dy / dx;
>+		lag_x = margin_distance / sqrt(gradient * gradient + 1);
>+		lag_y = sqrt((margin_distance + lag_x) *
>+			     (margin_distance - lag_x));
>+	} else {  /* Infinite gradient */
>+		lag_x = 0.0;
>+		lag_y = margin_distance;
>+	}
>+
>+	/*
>+	 * 'result' is the centre of an ellipse (radii a,b) which has been
>+	 * dragged by the finger moving inside it to 'in'. The finger is now
>+	 * touching the margin ellipse at some point: (Â±lag_x,Â±lag_y)
>+	 */
>+	result.x = (dx >= 0) ? in->x - lag_x : in->x + lag_x;
>+	result.y = (dy >= 0) ? in->y - lag_y : in->y + lag_y;
>+	return result;
> }
> 
> static inline struct libinput *
>-- 
>2.15.1
>

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