Fix screenshots and workspace switching; add configurable swipe bindings

compositor/src/gestures.rs

@@ -0,0 +1,134 @@
+//! A swipe commits once on release; cancelled and ambiguous gestures do nothing.
+
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+#[repr(u32)]
+pub(crate) enum SwipeDirection {
+    Up,
+    Down,
+    Left,
+    Right,
+}
+
+#[derive(Default)]
+pub(crate) struct Swipe {
+    delta: Option<(f64, f64)>,
+    threshold: f64,
+    fingers: u32,
+}
+
+impl Swipe {
+    pub fn begin(&mut self, fingers: u32, blocked: bool, threshold: u16) {
+        self.delta = ((3..=5).contains(&fingers) && !blocked).then_some((0.0, 0.0));
+        self.threshold = f64::from(threshold);
+        self.fingers = fingers;
+    }
+
+    pub fn fingers(&self) -> u32 {
+        self.fingers
+    }
+
+    pub fn active(&self) -> bool {
+        self.delta.is_some()
+    }
+
+    pub fn update(&mut self, dx: f64, dy: f64) {
+        if let Some((x, y)) = &mut self.delta {
+            *x += dx;
+            *y += dy;
+        }
+    }
+
+    pub fn finish(&mut self, cancelled: bool) -> Option<SwipeDirection> {
+        let (x, y) = self.delta.take()?;
+        if cancelled || !x.is_finite() || !y.is_finite() {
+            return None;
+        }
+        const DOMINANCE: f64 = 1.25;
+        if x.abs() >= self.threshold && x.abs() > y.abs() * DOMINANCE {
+            Some(if x < 0.0 {
+                SwipeDirection::Left
+            } else {
+                SwipeDirection::Right
+            })
+        } else if y.abs() >= self.threshold && y.abs() > x.abs() * DOMINANCE {
+            Some(if y < 0.0 {
+                SwipeDirection::Up
+            } else {
+                SwipeDirection::Down
+            })
+        } else {
+            None
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn a_swipe_accumulates_motion_and_commits_only_once_on_release() {
+        let mut swipe = Swipe::default();
+        swipe.begin(3, false, 80);
+        for _ in 0..10 {
+            swipe.update(-10.0, 1.0);
+        }
+        assert!(swipe.active());
+        assert_eq!(swipe.finish(false), Some(SwipeDirection::Left));
+        assert!(!swipe.active());
+        assert_eq!(swipe.finish(false), None);
+    }
+
+    #[test]
+    fn vertical_and_horizontal_swipes_are_distinct() {
+        for (delta, expected) in [
+            ((0.0, -100.0), SwipeDirection::Up),
+            ((0.0, 100.0), SwipeDirection::Down),
+            ((-100.0, 0.0), SwipeDirection::Left),
+            ((100.0, 0.0), SwipeDirection::Right),
+        ] {
+            let mut swipe = Swipe::default();
+            swipe.begin(3, false, 80);
+            swipe.update(delta.0, delta.1);
+            assert_eq!(swipe.finish(false), Some(expected));
+        }
+    }
+
+    #[test]
+    fn cancellation_jitter_diagonals_and_nonfinite_motion_do_not_navigate() {
+        for (x, y, cancelled) in [
+            (200.0, 0.0, true),
+            (79.0, 0.0, false),
+            (100.0, 100.0, false),
+            (f64::NAN, 100.0, false),
+        ] {
+            let mut swipe = Swipe::default();
+            swipe.begin(3, false, 80);
+            swipe.update(x, y);
+            assert_eq!(swipe.finish(cancelled), None);
+            assert!(!swipe.active());
+        }
+    }
+
+    #[test]
+    fn other_finger_counts_and_blocked_gestures_are_not_intercepted() {
+        for (fingers, blocked) in [(2, false), (6, false), (3, true)] {
+            let mut swipe = Swipe::default();
+            swipe.begin(fingers, blocked, 80);
+            assert!(!swipe.active());
+            swipe.update(200.0, 0.0);
+            assert_eq!(swipe.finish(false), None);
+        }
+    }
+
+    #[test]
+    fn configured_distance_changes_when_a_swipe_commits() {
+        let mut swipe = Swipe::default();
+        swipe.begin(3, false, 120);
+        swipe.update(100.0, 0.0);
+        assert_eq!(swipe.finish(false), None);
+        swipe.begin(3, false, 40);
+        swipe.update(100.0, 0.0);
+        assert_eq!(swipe.finish(false), Some(SwipeDirection::Right));
+    }
+}