feat: workspace switching touchpad gestures

src/backend/render/animations/mod.rs

@@ -0,0 +1 @@
+pub mod spring;

src/backend/render/animations/spring.rs

@@ -0,0 +1,138 @@
+// From Niri (GPL-3.0) https://github.com/YaLTeR/niri/tree/db49deb7fd2fbe805ceec060aa4dec65009ad7a7
+use std::time::Duration;
+
+#[derive(Debug, Clone, Copy)]
+pub struct SpringParams {
+    pub damping: f64,
+    pub mass: f64,
+    pub stiffness: f64,
+    pub epsilon: f64,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Spring {
+    pub from: f64,
+    pub to: f64,
+    pub initial_velocity: f64,
+    pub params: SpringParams,
+}
+
+impl SpringParams {
+    pub fn new(damping_ratio: f64, stiffness: f64, epsilon: f64) -> Self {
+        let damping_ratio = damping_ratio.max(0.);
+        let stiffness = stiffness.max(0.);
+        let epsilon = epsilon.max(0.);
+
+        let mass = 1.;
+        let critical_damping = 2. * (mass * stiffness).sqrt();
+        let damping = damping_ratio * critical_damping;
+
+        Self {
+            damping,
+            mass,
+            stiffness,
+            epsilon,
+        }
+    }
+}
+
+impl Spring {
+    pub fn value_at(&self, t: Duration) -> f64 {
+        self.oscillate(t.as_secs_f64())
+    }
+
+    // Based on libadwaita (LGPL-2.1-or-later):
+    // https://gitlab.gnome.org/GNOME/libadwaita/-/blob/1.4.4/src/adw-spring-animation.c,
+    // which itself is based on (MIT):
+    // https://github.com/robb/RBBAnimation/blob/master/RBBAnimation/RBBSpringAnimation.m
+    /// Computes and returns the duration until the spring is at rest.
+    pub fn duration(&self) -> Duration {
+        const DELTA: f64 = 0.001;
+
+        let beta = self.params.damping / (2. * self.params.mass);
+
+        if beta.abs() <= f64::EPSILON || beta < 0. {
+            return Duration::MAX;
+        }
+
+        let omega0 = (self.params.stiffness / self.params.mass).sqrt();
+
+        // As first ansatz for the overdamped solution,
+        // and general estimation for the oscillating ones
+        // we take the value of the envelope when it's < epsilon.
+        let mut x0 = -self.params.epsilon.ln() / beta;
+
+        // f64::EPSILON is too small for this specific comparison, so we use
+        // f32::EPSILON even though it's doubles.
+        if (beta - omega0).abs() <= f64::from(f32::EPSILON) || beta < omega0 {
+            return Duration::from_secs_f64(x0);
+        }
+
+        // Since the overdamped solution decays way slower than the envelope
+        // we need to use the value of the oscillation itself.
+        // Newton's root finding method is a good candidate in this particular case:
+        // https://en.wikipedia.org/wiki/Newton%27s_method
+        let mut y0 = self.oscillate(x0);
+        let m = (self.oscillate(x0 + DELTA) - y0) / DELTA;
+
+        let mut x1 = (self.to - y0 + m * x0) / m;
+        let mut y1 = self.oscillate(x1);
+
+        let mut i = 0;
+        while (self.to - y1).abs() > self.params.epsilon {
+            if i > 1000 {
+                return Duration::ZERO;
+            }
+
+            x0 = x1;
+            y0 = y1;
+
+            let m = (self.oscillate(x0 + DELTA) - y0) / DELTA;
+
+            x1 = (self.to - y0 + m * x0) / m;
+            y1 = self.oscillate(x1);
+            i += 1;
+        }
+
+        Duration::from_secs_f64(x1)
+    }
+
+    /// Returns the spring position at a given time in seconds.
+    fn oscillate(&self, t: f64) -> f64 {
+        let b = self.params.damping;
+        let m = self.params.mass;
+        let k = self.params.stiffness;
+        let v0 = self.initial_velocity;
+
+        let beta = b / (2. * m);
+        let omega0 = (k / m).sqrt();
+
+        let x0 = self.from - self.to;
+
+        let envelope = (-beta * t).exp();
+
+        // Solutions of the form C1*e^(lambda1*x) + C2*e^(lambda2*x)
+        // for the differential equation m*ẍ+b*ẋ+kx = 0
+
+        // f64::EPSILON is too small for this specific comparison, so we use
+        // f32::EPSILON even though it's doubles.
+        if (beta - omega0).abs() <= f64::from(f32::EPSILON) {
+            // Critically damped.
+            self.to + envelope * (x0 + (beta * x0 + v0) * t)
+        } else if beta < omega0 {
+            // Underdamped.
+            let omega1 = ((omega0 * omega0) - (beta * beta)).sqrt();
+
+            self.to
+                + envelope
+                    * (x0 * (omega1 * t).cos() + ((beta * x0 + v0) / omega1) * (omega1 * t).sin())
+        } else {
+            // Overdamped.
+            let omega2 = ((beta * beta) - (omega0 * omega0)).sqrt();
+
+            self.to
+                + envelope
+                    * (x0 * (omega2 * t).cosh() + ((beta * x0 + v0) / omega2) * (omega2 * t).sinh())
+        }
+    }
+}

src/backend/render/mod.rs

@@ -16,7 +16,7 @@ use crate::{
         grabs::{SeatMenuGrabState, SeatMoveGrabState},
         layout::tiling::ANIMATION_DURATION,
         CosmicMapped, CosmicMappedRenderElement, OverviewMode, SessionLock, Trigger,
-        WorkspaceRenderElement,
+        WorkspaceDelta, WorkspaceRenderElement,
     },
     state::{Common, Fps},
     utils::prelude::*,
@@ -70,6 +70,8 @@ use smithay::{
 };
 use tracing::warn;
 
+pub mod animations;
+
 pub mod cursor;
 use self::cursor::CursorRenderElement;
 pub mod element;
@@ -468,7 +470,7 @@ pub fn workspace_elements<R>(
     renderer: &mut R,
     state: &mut Common,
     output: &Output,
-    previous: Option<(WorkspaceHandle, usize, Instant)>,
+    previous: Option<(WorkspaceHandle, usize, WorkspaceDelta)>,
     current: (WorkspaceHandle, usize),
     cursor_mode: CursorMode,
     _fps: &mut Option<&mut Fps>,
@@ -684,10 +686,18 @@ where
             let has_fullscreen = workspace.fullscreen.is_some();
             let is_active_space = workspace.outputs().any(|o| o == &active_output);
 
-            let percentage = {
-                let percentage = Instant::now().duration_since(*start).as_millis() as f32
-                    / ANIMATION_DURATION.as_millis() as f32;
-                ease(EaseInOutCubic, 0.0, 1.0, percentage)
+            let percentage = match start {
+                WorkspaceDelta::Shortcut(st) => ease(
+                    EaseInOutCubic,
+                    0.0,
+                    1.0,
+                    Instant::now().duration_since(*st).as_millis() as f32
+                        / ANIMATION_DURATION.as_millis() as f32,
+                ),
+                WorkspaceDelta::Gesture(prog) => *prog as f32,
+                WorkspaceDelta::GestureEnd(st, spring) => {
+                    (spring.value_at(Instant::now().duration_since(*st)) as f32).clamp(0.0, 1.0)
+                }
             };
             let offset = Point::<i32, Logical>::from(match (layout, *previous_idx < current.1) {
                 (WorkspaceLayout::Vertical, true) => {
@@ -1012,7 +1022,7 @@ pub fn render_workspace<R, Target, OffTarget, Source>(
     age: usize,
     state: &mut Common,
     output: &Output,
-    previous: Option<(WorkspaceHandle, usize, Instant)>,
+    previous: Option<(WorkspaceHandle, usize, WorkspaceDelta)>,
     current: (WorkspaceHandle, usize),
     mut cursor_mode: CursorMode,
     screencopy: Option<(Source, &[(ScreencopySession, BufferParams)])>,

src/input/gestures/mod.rs

@@ -0,0 +1,176 @@
+use smithay::utils::{Logical, Point};
+use std::{collections::VecDeque, time::Duration};
+use tracing::trace;
+
+use crate::shell::Direction;
+
+const HISTORY_LIMIT: Duration = Duration::from_millis(150);
+const DECELERATION_TOUCHPAD: f64 = 0.997;
+
+#[derive(Debug, Clone, Copy)]
+pub struct SwipeEvent {
+    delta: f64,
+    timestamp: Duration,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub enum SwipeAction {
+    NextWorkspace,
+    PrevWorkspace,
+}
+
+#[derive(Debug, Clone)]
+pub struct GestureState {
+    pub fingers: u32,
+    pub direction: Option<Direction>,
+    pub action: Option<SwipeAction>,
+    pub delta: f64,
+    // Delta tracking inspired by Niri (GPL-3.0) https://github.com/YaLTeR/niri/tree/v0.1.3
+    pub history: VecDeque<SwipeEvent>,
+}
+
+impl GestureState {
+    pub fn new(fingers: u32) -> Self {
+        GestureState {
+            fingers,
+            direction: None,
+            action: None,
+            delta: 0.0,
+            history: VecDeque::new(),
+        }
+    }
+
+    pub fn update(&mut self, movement: Point<f64, Logical>, timestamp: Duration) -> bool {
+        let first_update = self.direction.is_none();
+
+        if first_update {
+            // Find proper direction
+            self.direction = if movement.x.abs() > movement.y.abs() {
+                if movement.x > 0.0 {
+                    Some(Direction::Right)
+                } else {
+                    Some(Direction::Left)
+                }
+            } else {
+                if movement.y > 0.0 {
+                    Some(Direction::Down)
+                } else {
+                    Some(Direction::Up)
+                }
+            }
+        }
+
+        let delta = match self.direction {
+            Some(Direction::Left) => -movement.x,
+            Some(Direction::Right) => movement.x,
+            Some(Direction::Up) => -movement.y,
+            Some(Direction::Down) => movement.y,
+            None => 0.0,
+        };
+
+        self.push(delta, timestamp);
+        first_update
+    }
+
+    /// Pushes a new reading into the tracker.
+    fn push(&mut self, delta: f64, timestamp: Duration) {
+        // For the events that we care about, timestamps should always increase
+        // monotonically.
+        if let Some(last) = self.history.back() {
+            if timestamp < last.timestamp {
+                trace!(
+                    "ignoring event with timestamp {timestamp:?} earlier than last {:?}",
+                    last.timestamp
+                );
+                return;
+            }
+        }
+
+        self.history.push_back(SwipeEvent { delta, timestamp });
+        self.delta += delta;
+
+        self.trim_history();
+    }
+
+    /// Computes the current gesture velocity.
+    pub fn velocity(&self) -> f64 {
+        let (Some(first), Some(last)) = (self.history.front(), self.history.back()) else {
+            return 0.;
+        };
+
+        let total_time = (last.timestamp - first.timestamp).as_secs_f64();
+        if total_time == 0. {
+            return 0.;
+        }
+
+        let total_delta = self.history.iter().map(|event| event.delta).sum::<f64>();
+        total_delta / total_time
+    }
+
+    /// Computes the gesture end position after decelerating to a halt.
+    pub fn projected_end_pos(&self) -> f64 {
+        let vel = self.velocity();
+        self.delta - vel / (1000. * DECELERATION_TOUCHPAD.ln())
+    }
+
+    fn trim_history(&mut self) {
+        let Some(&SwipeEvent { timestamp, .. }) = self.history.back() else {
+            return;
+        };
+
+        while let Some(first) = self.history.front() {
+            if timestamp <= first.timestamp + HISTORY_LIMIT {
+                break;
+            }
+
+            let _ = self.history.pop_front();
+        }
+    }
+}
+
+impl Default for GestureState {
+    fn default() -> Self {
+        GestureState::new(0)
+    }
+}
+
+// rubber_band.rs from Niri (GPL-3.0) https://github.com/YaLTeR/niri/blob/db49deb7fd2fbe805ceec060aa4dec65009ad7a7/src/rubber_band.rs
+#[derive(Debug, Clone, Copy)]
+pub struct RubberBand {
+    pub stiffness: f64,
+    pub limit: f64,
+}
+
+impl RubberBand {
+    pub fn band(&self, x: f64) -> f64 {
+        let c = self.stiffness;
+        let d = self.limit;
+
+        (1. - (1. / (x * c / d + 1.))) * d
+    }
+
+    pub fn derivative(&self, x: f64) -> f64 {
+        let c = self.stiffness;
+        let d = self.limit;
+
+        c * d * d / (c * x + d).powi(2)
+    }
+
+    pub fn clamp(&self, min: f64, max: f64, x: f64) -> f64 {
+        let clamped = x.clamp(min, max);
+        let sign = if x < clamped { -1. } else { 1. };
+        let diff = (x - clamped).abs();
+
+        clamped + sign * self.band(diff)
+    }
+
+    pub fn clamp_derivative(&self, min: f64, max: f64, x: f64) -> f64 {
+        if min <= x && x <= max {
+            return 1.;
+        }
+
+        let clamped = x.clamp(min, max);
+        let diff = (x - clamped).abs();
+        self.derivative(diff)
+    }
+}

src/input/mod.rs

@@ -3,6 +3,7 @@
 use crate::{
     backend::render::cursor::CursorState,
     config::{xkb_config_to_wl, Action, Config, KeyModifiers, KeyPattern},
+    input::gestures::{GestureState, SwipeAction},
     shell::{
         focus::{target::PointerFocusTarget, FocusDirection},
         grabs::{ResizeEdge, SeatMenuGrabState, SeatMoveGrabState},
@@ -10,7 +11,8 @@ use crate::{
             floating::ResizeGrabMarker,
             tiling::{SwapWindowGrab, TilingLayout},
         },
-        Direction, FocusResult, MoveResult, OverviewMode, ResizeDirection, ResizeMode, Trigger,
+        Direction, FocusResult, InvalidWorkspaceIndex, MoveResult, OverviewMode, ResizeDirection,
+        ResizeMode, Trigger, WorkspaceDelta,
     },
     state::Common,
     utils::prelude::*,
@@ -68,6 +70,8 @@ use std::{
 
 crate::utils::id_gen!(next_seat_id, SEAT_ID, SEAT_IDS);
 
+pub mod gestures;
+
 #[repr(transparent)]
 pub struct SeatId(pub usize);
 pub struct ActiveOutput(pub RefCell<Output>);
@@ -1071,42 +1075,127 @@ impl State {
             }
             InputEvent::GestureSwipeBegin { event, .. } => {
                 if let Some(seat) = self.common.seat_with_device(&event.device()) {
-                    let serial = SERIAL_COUNTER.next_serial();
-                    let pointer = seat.get_pointer().unwrap();
-                    pointer.gesture_swipe_begin(
-                        self,
-                        &GestureSwipeBeginEvent {
-                            serial,
-                            time: event.time_msec(),
-                            fingers: event.fingers(),
-                        },
-                    );
+                    if event.fingers() >= 3 {
+                        self.common.gesture_state = Some(GestureState::new(event.fingers()));
+                    } else {
+                        let serial = SERIAL_COUNTER.next_serial();
+                        let pointer = seat.get_pointer().unwrap();
+                        pointer.gesture_swipe_begin(
+                            self,
+                            &GestureSwipeBeginEvent {
+                                serial,
+                                time: event.time_msec(),
+                                fingers: event.fingers(),
+                            },
+                        );
+                    }
                 }
             }
             InputEvent::GestureSwipeUpdate { event, .. } => {
-                if let Some(seat) = self.common.seat_with_device(&event.device()) {
-                    let pointer = seat.get_pointer().unwrap();
-                    pointer.gesture_swipe_update(
-                        self,
-                        &GestureSwipeUpdateEvent {
-                            time: event.time_msec(),
-                            delta: event.delta(),
-                        },
-                    );
+                if let Some(seat) = self.common.seat_with_device(&event.device()).cloned() {
+                    let mut activate_action: Option<SwipeAction> = None;
+                    if let Some(ref mut gesture_state) = self.common.gesture_state {
+                        let first_update = gesture_state.update(
+                            event.delta(),
+                            Duration::from_millis(event.time_msec() as u64),
+                        );
+                        // Decide on action if first update
+                        if first_update {
+                            activate_action = match gesture_state.fingers {
+                                3 => None, // TODO: 3 finger gestures
+                                4 => {
+                                    if self.common.config.cosmic_conf.workspaces.workspace_layout
+                                        == WorkspaceLayout::Horizontal
+                                    {
+                                        match gesture_state.direction {
+                                            Some(Direction::Left) => {
+                                                Some(SwipeAction::NextWorkspace)
+                                            }
+                                            Some(Direction::Right) => {
+                                                Some(SwipeAction::PrevWorkspace)
+                                            }
+                                            _ => None, // TODO: Other actions
+                                        }
+                                    } else {
+                                        match gesture_state.direction {
+                                            Some(Direction::Up) => Some(SwipeAction::NextWorkspace),
+                                            Some(Direction::Down) => {
+                                                Some(SwipeAction::PrevWorkspace)
+                                            }
+                                            _ => None, // TODO: Other actions
+                                        }
+                                    }
+                                }
+                                _ => None,
+                            };
+
+                            gesture_state.action = activate_action;
+                        }
+
+                        match gesture_state.action {
+                            Some(SwipeAction::NextWorkspace) | Some(SwipeAction::PrevWorkspace) => {
+                                self.common.shell.update_workspace_delta(
+                                    &seat.active_output(),
+                                    gesture_state.delta,
+                                )
+                            }
+                            _ => {}
+                        }
+                    } else {
+                        let pointer = seat.get_pointer().unwrap();
+                        pointer.gesture_swipe_update(
+                            self,
+                            &GestureSwipeUpdateEvent {
+                                time: event.time_msec(),
+                                delta: event.delta(),
+                            },
+                        );
+                    }
+                    match activate_action {
+                        Some(SwipeAction::NextWorkspace) => {
+                            let _ = self.to_next_workspace(&seat, true);
+                        }
+                        Some(SwipeAction::PrevWorkspace) => {
+                            let _ = self.to_previous_workspace(&seat, true);
+                        }
+                        _ => {}
+                    }
                 }
             }
             InputEvent::GestureSwipeEnd { event, .. } => {
-                if let Some(seat) = self.common.seat_with_device(&event.device()) {
-                    let serial = SERIAL_COUNTER.next_serial();
-                    let pointer = seat.get_pointer().unwrap();
-                    pointer.gesture_swipe_end(
-                        self,
-                        &GestureSwipeEndEvent {
-                            serial,
-                            time: event.time_msec(),
-                            cancelled: event.cancelled(),
-                        },
-                    );
+                if let Some(seat) = self.common.seat_with_device(&event.device()).cloned() {
+                    if let Some(ref gesture_state) = self.common.gesture_state {
+                        match gesture_state.action {
+                            Some(SwipeAction::NextWorkspace) | Some(SwipeAction::PrevWorkspace) => {
+                                let velocity = gesture_state.velocity();
+                                let norm_velocity =
+                                    if self.common.config.cosmic_conf.workspaces.workspace_layout
+                                        == WorkspaceLayout::Horizontal
+                                    {
+                                        velocity / seat.active_output().geometry().size.w as f64
+                                    } else {
+                                        velocity / seat.active_output().geometry().size.h as f64
+                                    };
+                                let _ = self
+                                    .common
+                                    .shell
+                                    .end_workspace_swipe(&seat.active_output(), norm_velocity);
+                            }
+                            _ => {}
+                        }
+                        self.common.gesture_state = None;
+                    } else {
+                        let serial = SERIAL_COUNTER.next_serial();
+                        let pointer = seat.get_pointer().unwrap();
+                        pointer.gesture_swipe_end(
+                            self,
+                            &GestureSwipeEndEvent {
+                                serial,
+                                time: event.time_msec(),
+                                cancelled: event.cancelled(),
+                            },
+                        );
+                    }
                 }
             }
             InputEvent::GesturePinchBegin { event, .. } => {
@@ -1471,10 +1560,11 @@ impl State {
                     0 => 9,
                     x => x - 1,
                 };
-                let _ = self
-                    .common
-                    .shell
-                    .activate(&current_output, workspace as usize);
+                let _ = self.common.shell.activate(
+                    &current_output,
+                    workspace as usize,
+                    WorkspaceDelta::new_shortcut(),
+                );
             }
             Action::LastWorkspace => {
                 let current_output = seat.active_output();
@@ -1484,24 +1574,14 @@ impl State {
                     .workspaces
                     .len(&current_output)
                     .saturating_sub(1);
-                let _ = self.common.shell.activate(&current_output, workspace);
+                let _ = self.common.shell.activate(
+                    &current_output,
+                    workspace,
+                    WorkspaceDelta::new_shortcut(),
+                );
             }
             Action::NextWorkspace => {
-                let current_output = seat.active_output();
-                let workspace = self
-                    .common
-                    .shell
-                    .workspaces
-                    .active_num(&current_output)
-                    .1
-                    .saturating_add(1);
-                if self
-                    .common
-                    .shell
-                    .activate(&current_output, workspace)
-                    .is_err()
-                    && propagate
-                {
+                if self.to_next_workspace(seat, false).is_err() && propagate {
                     if let Some(inferred) = pattern.inferred_direction() {
                         self.handle_action(
                             Action::SwitchOutput(inferred),
@@ -1516,21 +1596,7 @@ impl State {
                 }
             }
             Action::PreviousWorkspace => {
-                let current_output = seat.active_output();
-                let workspace = self
-                    .common
-                    .shell
-                    .workspaces
-                    .active_num(&current_output)
-                    .1
-                    .saturating_sub(1);
-                if self
-                    .common
-                    .shell
-                    .activate(&current_output, workspace)
-                    .is_err()
-                    && propagate
-                {
+                if self.to_previous_workspace(seat, false).is_err() && propagate {
                     if let Some(inferred) = pattern.inferred_direction() {
                         self.handle_action(
                             Action::SwitchOutput(inferred),
@@ -1663,7 +1729,11 @@ impl State {
 
                 if let Some(next_output) = next_output {
                     let idx = self.common.shell.workspaces.active_num(&next_output).1;
-                    match self.common.shell.activate(&next_output, idx) {
+                    match self.common.shell.activate(
+                        &next_output,
+                        idx,
+                        WorkspaceDelta::new_shortcut(),
+                    ) {
                         Ok(Some(new_pos)) => {
                             seat.set_active_output(&next_output);
                             if let Some(ptr) = seat.get_pointer() {
@@ -1726,7 +1796,11 @@ impl State {
                     .cloned();
                 if let Some(next_output) = next_output {
                     let idx = self.common.shell.workspaces.active_num(&next_output).1;
-                    match self.common.shell.activate(&next_output, idx) {
+                    match self.common.shell.activate(
+                        &next_output,
+                        idx,
+                        WorkspaceDelta::new_shortcut(),
+                    ) {
                         Ok(Some(new_pos)) => {
                             seat.set_active_output(&next_output);
                             if let Some(ptr) = seat.get_pointer() {
@@ -1762,7 +1836,11 @@ impl State {
                     .cloned();
                 if let Some(prev_output) = prev_output {
                     let idx = self.common.shell.workspaces.active_num(&prev_output).1;
-                    match self.common.shell.activate(&prev_output, idx) {
+                    match self.common.shell.activate(
+                        &prev_output,
+                        idx,
+                        WorkspaceDelta::new_shortcut(),
+                    ) {
                         Ok(Some(new_pos)) => {
                             seat.set_active_output(&prev_output);
                             if let Some(ptr) = seat.get_pointer() {
@@ -2271,6 +2349,56 @@ impl State {
             None
         }
     }
+
+    pub fn to_next_workspace(
+        &mut self,
+        seat: &Seat<State>,
+        gesture: bool,
+    ) -> Result<Option<Point<i32, Global>>, InvalidWorkspaceIndex> {
+        let current_output = seat.active_output();
+        let workspace = self
+            .common
+            .shell
+            .workspaces
+            .active_num(&current_output)
+            .1
+            .saturating_add(1);
+
+        self.common.shell.activate(
+            &current_output,
+            workspace,
+            if gesture {
+                WorkspaceDelta::new_gesture()
+            } else {
+                WorkspaceDelta::new_shortcut()
+            },
+        )
+    }
+
+    pub fn to_previous_workspace(
+        &mut self,
+        seat: &Seat<State>,
+        gesture: bool,
+    ) -> Result<Option<Point<i32, Global>>, InvalidWorkspaceIndex> {
+        let current_output = seat.active_output();
+        let workspace = self
+            .common
+            .shell
+            .workspaces
+            .active_num(&current_output)
+            .1
+            .saturating_sub(1);
+
+        self.common.shell.activate(
+            &current_output,
+            workspace,
+            if gesture {
+                WorkspaceDelta::new_gesture()
+            } else {
+                WorkspaceDelta::new_shortcut()
+            },
+        )
+    }
 }
 
 fn sessions_for_output(state: &Common, output: &Output) -> impl Iterator<Item = Session> {

src/shell/mod.rs

@@ -46,6 +46,7 @@ use smithay::{
 };
 
 use crate::{
+    backend::render::animations::spring::{Spring, SpringParams},
     config::{Config, KeyModifiers, KeyPattern},
     state::client_should_see_privileged_protocols,
     utils::prelude::*,
@@ -93,6 +94,9 @@ use self::{
 };
 
 const ANIMATION_DURATION: Duration = Duration::from_millis(200);
+const GESTURE_MAX_LENGTH: f64 = 150.0;
+const GESTURE_POSITION_THRESHOLD: f64 = 0.5;
+const GESTURE_VELOCITY_THRESHOLD: f64 = 0.02;
 
 #[derive(Debug, Clone)]
 pub enum Trigger {
@@ -223,9 +227,41 @@ pub struct SessionLock {
     pub surfaces: HashMap<Output, LockSurface>,
 }
 
+#[derive(Debug, Clone, Copy)]
+pub enum WorkspaceDelta {
+    Shortcut(Instant),
+    Gesture(f64),
+    GestureEnd(Instant, Spring),
+    // InvalidGesture(f64), TODO
+    // InvalidGestureEnd(Instant, Spring), TODO
+}
+
+impl WorkspaceDelta {
+    pub fn new_gesture() -> Self {
+        WorkspaceDelta::Gesture(0.0)
+    }
+
+    pub fn new_gesture_end(delta: f64, velocity: f64) -> Self {
+        let params: SpringParams = SpringParams::new(1.0, 1000.0, 0.0001);
+        WorkspaceDelta::GestureEnd(
+            Instant::now(),
+            Spring {
+                from: delta,
+                to: 1.0,
+                initial_velocity: velocity,
+                params,
+            },
+        )
+    }
+
+    pub fn new_shortcut() -> Self {
+        WorkspaceDelta::Shortcut(Instant::now())
+    }
+}
+
 #[derive(Debug)]
 pub struct WorkspaceSet {
-    previously_active: Option<(usize, Instant)>,
+    previously_active: Option<(usize, WorkspaceDelta)>,
     active: usize,
     pub group: WorkspaceGroupHandle,
     idx: usize,
@@ -371,6 +407,7 @@ impl WorkspaceSet {
     fn activate(
         &mut self,
         idx: usize,
+        workspace_delta: WorkspaceDelta,
         state: &mut WorkspaceUpdateGuard<'_, State>,
     ) -> Result<bool, InvalidWorkspaceIndex> {
         if idx >= self.workspaces.len() {
@@ -383,15 +420,36 @@ impl WorkspaceSet {
             state.remove_workspace_state(&self.workspaces[old_active].handle, WState::Urgent);
             state.remove_workspace_state(&self.workspaces[idx].handle, WState::Urgent);
             state.add_workspace_state(&self.workspaces[idx].handle, WState::Active);
-
-            self.previously_active = Some((old_active, Instant::now()));
+            self.previously_active = Some((old_active, workspace_delta));
             self.active = idx;
             Ok(true)
         } else {
+            if let Some((p_idx, _)) = self.previously_active {
+                self.previously_active = Some((p_idx, workspace_delta));
+                return Ok(true);
+            }
             Ok(false)
         }
     }
 
+    fn activate_previous(
+        &mut self,
+        workspace_delta: WorkspaceDelta,
+        state: &mut WorkspaceUpdateGuard<'_, State>,
+    ) -> Result<bool, InvalidWorkspaceIndex> {
+        if let Some((idx, _)) = self.previously_active {
+            return self.activate(idx, workspace_delta, state);
+        }
+        Err(InvalidWorkspaceIndex)
+    }
+
+    fn update_workspace_delta(&mut self, delta: f64) {
+        let easing = delta.clamp(0.0, GESTURE_MAX_LENGTH).abs() / GESTURE_MAX_LENGTH;
+        if let Some((idx, _)) = self.previously_active {
+            self.previously_active = Some((idx, WorkspaceDelta::Gesture(easing)));
+        }
+    }
+
     fn set_output(
         &mut self,
         new_output: &Output,
@@ -410,8 +468,21 @@ impl WorkspaceSet {
 
     fn refresh<'a>(&mut self, xdg_activation_state: &XdgActivationState) {
         if let Some((_, start)) = self.previously_active {
-            if Instant::now().duration_since(start).as_millis() >= ANIMATION_DURATION.as_millis() {
-                self.previously_active = None;
+            match start {
+                WorkspaceDelta::Shortcut(st) => {
+                    if Instant::now().duration_since(st).as_millis() as f32
+                        >= ANIMATION_DURATION.as_millis() as f32
+                    {
+                        self.previously_active = None;
+                    }
+                }
+                WorkspaceDelta::GestureEnd(st, spring) => {
+                    if Instant::now().duration_since(st).as_millis() > spring.duration().as_millis()
+                    {
+                        self.previously_active = None;
+                    }
+                }
+                _ => {}
             }
         } else {
             self.workspaces[self.active].refresh(xdg_activation_state);
@@ -855,7 +926,7 @@ impl Workspaces {
             .and_then(|set| set.workspaces.get_mut(num))
     }
 
-    pub fn active(&self, output: &Output) -> (Option<(&Workspace, Instant)>, &Workspace) {
+    pub fn active(&self, output: &Output) -> (Option<(&Workspace, WorkspaceDelta)>, &Workspace) {
         let set = self.sets.get(output).or(self.backup_set.as_ref()).unwrap();
         (
             set.previously_active
@@ -1095,6 +1166,7 @@ impl Shell {
         &mut self,
         output: &Output,
         idx: usize,
+        workspace_delta: WorkspaceDelta,
     ) -> Result<Option<Point<i32, Global>>, InvalidWorkspaceIndex> {
         match &mut self.workspaces.mode {
             WorkspaceMode::OutputBound => {
@@ -1105,7 +1177,7 @@ impl Shell {
                     ) {
                         set.workspaces[set.active].tiling_layer.cleanup_drag();
                     }
-                    set.activate(idx, &mut self.workspace_state.update())?;
+                    set.activate(idx, workspace_delta, &mut self.workspace_state.update())?;
                     if let Some(xwm) = self
                         .xwayland_state
                         .as_mut()
@@ -1151,7 +1223,143 @@ impl Shell {
             }
             WorkspaceMode::Global => {
                 for set in self.workspaces.sets.values_mut() {
-                    set.activate(idx, &mut self.workspace_state.update())?;
+                    set.activate(idx, workspace_delta, &mut self.workspace_state.update())?;
+                }
+                Ok(None)
+            }
+        }
+    }
+
+    pub fn update_workspace_delta(&mut self, output: &Output, delta: f64) {
+        match &mut self.workspaces.mode {
+            WorkspaceMode::OutputBound => {
+                if let Some(set) = self.workspaces.sets.get_mut(output) {
+                    set.update_workspace_delta(delta);
+                }
+            }
+            WorkspaceMode::Global => {
+                for set in self.workspaces.sets.values_mut() {
+                    set.update_workspace_delta(delta);
+                }
+            }
+        }
+    }
+
+    pub fn end_workspace_swipe(
+        &mut self,
+        output: &Output,
+        velocity: f64,
+    ) -> Result<Option<Point<i32, Global>>, InvalidWorkspaceIndex> {
+        match &mut self.workspaces.mode {
+            WorkspaceMode::OutputBound => {
+                if let Some(set) = self.workspaces.sets.get_mut(output) {
+                    if matches!(
+                        self.overview_mode,
+                        OverviewMode::Started(Trigger::Pointer(_), _)
+                    ) {
+                        set.workspaces[set.active].tiling_layer.cleanup_drag();
+                    }
+                    if let Some((_, workspace_delta)) = set.previously_active {
+                        match workspace_delta {
+                            WorkspaceDelta::Gesture(delta) => {
+                                if (velocity > 0.0 && velocity.abs() >= GESTURE_VELOCITY_THRESHOLD)
+                                    || (velocity.abs() < GESTURE_VELOCITY_THRESHOLD
+                                        && delta.abs() > GESTURE_POSITION_THRESHOLD)
+                                {
+                                    set.activate(
+                                        set.active,
+                                        WorkspaceDelta::new_gesture_end(
+                                            delta.abs(),
+                                            velocity.abs(),
+                                        ),
+                                        &mut self.workspace_state.update(),
+                                    )?;
+                                } else {
+                                    set.activate_previous(
+                                        WorkspaceDelta::new_gesture_end(
+                                            1.0 - delta.abs(),
+                                            velocity.abs(),
+                                        ),
+                                        &mut self.workspace_state.update(),
+                                    )?;
+                                }
+                            }
+                            _ => {} // Do nothing
+                        }
+                    }
+                    if let Some(xwm) = self
+                        .xwayland_state
+                        .as_mut()
+                        .and_then(|state| state.xwm.as_mut())
+                    {
+                        {
+                            for window in set.workspaces[set.active]
+                                .tiling_layer
+                                .mapped()
+                                .map(|(w, _)| w)
+                                .chain(set.workspaces[set.active].floating_layer.space.elements())
+                            {
+                                if let Some(surf) = window.active_window().x11_surface() {
+                                    let _ = xwm.raise_window(surf);
+                                }
+                            }
+                            for window in set.sticky_layer.space.elements() {
+                                if let Some(surf) = window.active_window().x11_surface() {
+                                    let _ = xwm.raise_window(surf);
+                                }
+                            }
+                            if let Some(surf) = set.workspaces[set.active]
+                                .fullscreen
+                                .as_ref()
+                                .and_then(|f| f.surface.x11_surface())
+                            {
+                                let _ = xwm.raise_window(surf);
+                            }
+                        }
+                        for surface in &self.override_redirect_windows {
+                            let _ = xwm.raise_window(surface);
+                        }
+                    }
+
+                    let output_geo = output.geometry();
+                    Ok(Some(
+                        output_geo.loc
+                            + Point::from((output_geo.size.w / 2, output_geo.size.h / 2)),
+                    ))
+                } else {
+                    Ok(None)
+                }
+            }
+            WorkspaceMode::Global => {
+                for set in self.workspaces.sets.values_mut() {
+                    if let Some((_, workspace_delta)) = set.previously_active {
+                        match workspace_delta {
+                            WorkspaceDelta::Gesture(delta) => {
+                                if (velocity > 0.0 && velocity.abs() >= GESTURE_VELOCITY_THRESHOLD)
+                                    || (velocity.abs() < GESTURE_VELOCITY_THRESHOLD
+                                        && delta.abs() > GESTURE_POSITION_THRESHOLD)
+                                {
+                                    set.activate(
+                                        set.active,
+                                        WorkspaceDelta::new_gesture_end(
+                                            delta.abs(),
+                                            velocity.abs(),
+                                        ),
+                                        &mut self.workspace_state.update(),
+                                    )?;
+                                } else {
+                                    set.activate_previous(
+                                        WorkspaceDelta::new_gesture_end(
+                                            1.0 - delta.abs(),
+                                            velocity.abs(),
+                                        ),
+                                        &mut self.workspace_state.update(),
+                                    )?;
+                                }
+                            }
+                            _ => {} // Do nothing
+                        }
+                    }
                 }
                 Ok(None)
             }
@@ -1923,7 +2131,13 @@ impl Shell {
                 .shell
                 .workspaces
                 .idx_for_handle(&to_output, to)
-                .and_then(|to_idx| state.common.shell.activate(&to_output, to_idx).unwrap())
+                .and_then(|to_idx| {
+                    state
+                        .common
+                        .shell
+                        .activate(&to_output, to_idx, WorkspaceDelta::new_shortcut())
+                        .unwrap()
+                })
         } else {
             None
         };

src/state.rs

@@ -3,7 +3,7 @@
 use crate::{
     backend::{kms::KmsState, winit::WinitState, x11::X11State},
     config::{Config, OutputConfig},
-    input::Devices,
+    input::{gestures::GestureState, Devices},
     shell::{grabs::SeatMoveGrabState, Shell},
     utils::prelude::*,
     wayland::protocols::{
@@ -159,6 +159,7 @@ pub struct Common {
     pub clock: Clock<Monotonic>,
     pub should_stop: bool,
     pub local_offset: time::UtcOffset,
+    pub gesture_state: Option<GestureState>,
 
     pub theme: cosmic::Theme,
 
@@ -423,6 +424,7 @@ impl State {
 
                 clock,
                 should_stop: false,
+                gesture_state: None,
 
                 theme: cosmic::theme::system_preference(),
 

src/wayland/handlers/toplevel_management.rs

@@ -10,7 +10,7 @@ use smithay::{
 };
 
 use crate::{
-    shell::{CosmicSurface, Shell},
+    shell::{CosmicSurface, Shell, WorkspaceDelta},
     utils::prelude::*,
     wayland::protocols::{
         toplevel_info::ToplevelInfoHandler,
@@ -60,7 +60,11 @@ impl ToplevelManagementHandler for State {
                     .unwrap()
                     .clone();
 
-                let _ = self.common.shell.activate(&output, idx as usize); // TODO: Move pointer?
+                let _ = self.common.shell.activate(
+                    &output,
+                    idx as usize,
+                    WorkspaceDelta::new_shortcut(),
+                ); // TODO: Move pointer?
                 mapped.focus_window(window);
                 Common::set_focus(self, Some(&mapped.clone().into()), &seat, None);
                 return;

src/wayland/handlers/workspace.rs

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-3.0-only
 
 use crate::{
+    shell::WorkspaceDelta,
     state::ClientState,
     utils::prelude::*,
     wayland::protocols::workspace::{
@@ -38,7 +39,11 @@ impl WorkspaceHandler for State {
                     });
 
                     if let Some((output, idx)) = maybe {
-                        let _ = self.common.shell.activate(&output, idx); // TODO: move cursor?
+                        let _ = self.common.shell.activate(
+                            &output,
+                            idx,
+                            WorkspaceDelta::new_shortcut(),
+                        ); // TODO: move cursor?
                     }
                 }
                 Request::SetTilingState { workspace, state } => {