zng_ext_input/

touch.rs

//! Touch events and service.
//!
//! The app extension [`TouchManager`] provides the events and service. It is included in the default application.

use std::{collections::HashMap, mem, num::NonZeroU32, ops, time::Duration};
use zng_app::{
    AppExtension, DInstant,
    event::{AnyEventArgs, EventPropagationHandle, event, event_args},
    shortcut::ModifiersState,
    timer::{DeadlineVar, TIMERS},
    update::EventUpdate,
    view_process::{
        VIEW_PROCESS_INITED_EVENT,
        raw_device_events::DeviceId,
        raw_events::{RAW_FRAME_RENDERED_EVENT, RAW_MOUSE_LEFT_EVENT, RAW_TOUCH_CONFIG_CHANGED_EVENT, RAW_TOUCH_EVENT, RawTouchArgs},
    },
    widget::{
        WIDGET, WidgetId,
        info::{HitTestInfo, InteractionPath, WIDGET_INFO_CHANGED_EVENT},
    },
    window::WindowId,
};

use zng_app_context::app_local;
use zng_ext_window::{NestedWindowWidgetInfoExt as _, WINDOWS};
use zng_layout::unit::{
    AngleRadian, Dip, DipPoint, DipToPx, DipVector, Factor, Px, PxPoint, PxToDip, PxTransform, PxVector, TimeUnits, euclid,
};
use zng_var::{ArcVar, ReadOnlyArcVar, Var, impl_from_and_into_var, types::ArcCowVar, var};
pub use zng_view_api::{
    config::TouchConfig,
    touch::{TouchForce, TouchId, TouchPhase, TouchUpdate},
};

use crate::{
    keyboard::MODIFIERS_CHANGED_EVENT,
    pointer_capture::{CaptureInfo, POINTER_CAPTURE, POINTER_CAPTURE_EVENT},
};

/// Application extension that provides touch events and service.
///
/// # Events
///
/// Events this extension provides.
///
/// * [`TOUCH_MOVE_EVENT`]
/// * [`TOUCH_INPUT_EVENT`]
/// * [`TOUCHED_EVENT`]
/// * [`TOUCH_TAP_EVENT`]
/// * [`TOUCH_TRANSFORM_EVENT`]
/// * [`TOUCH_LONG_PRESS_EVENT`]
///
/// # Services
///
/// Services this extension provides.
///
/// * [`TOUCH`]
#[derive(Default)]
pub struct TouchManager {
    modifiers: ModifiersState,
    pressed: HashMap<TouchId, PressedInfo>,
    tap_gesture: TapGesture,
    transform_gesture: TransformGesture,
    long_press_gesture: LongPressGesture,
    mouse_touch: Option<TouchId>,
}
struct PressedInfo {
    touch_propagation: EventPropagationHandle,
    target: InteractionPath,
    device_id: DeviceId,
    position: DipPoint,
    force: Option<TouchForce>,
    hits: HitTestInfo,
    velocity_samples: Vec<(DInstant, DipPoint)>,
}
impl PressedInfo {
    fn push_velocity_sample(&mut self, timestamp: DInstant, position: DipPoint) {
        if let Some(last) = self.velocity_samples.last_mut() {
            if timestamp.duration_since(last.0) < 1.ms() {
                last.1 = position;
                return;
            }
        }

        if self.velocity_samples.len() == 4 {
            self.velocity_samples.remove(0);
        }
        self.velocity_samples.push((timestamp, position));
    }

    fn velocity(&self) -> DipVector {
        if self.velocity_samples.len() < 4 {
            DipVector::zero()
        } else {
            let samples = [
                self.velocity_samples[0].1.cast::<f64>(),
                self.velocity_samples[1].1.cast(),
                self.velocity_samples[2].1.cast(),
                self.velocity_samples[3].1.cast(),
            ];
            let velocity_at = |end_i: usize| {
                let start_i = end_i - 1;

                let start_t = self.velocity_samples[start_i].0;
                let end_t = self.velocity_samples[end_i].0;

                let start_s = samples[start_i];
                let end_s = samples[end_i];

                let delta = (end_t - start_t).as_secs_f64();

                if delta > 0.0 {
                    (end_s - start_s) / delta
                } else {
                    euclid::vec2(0.0, 0.0)
                }
            };

            let v23 = velocity_at(3) * 0.6;
            let v12 = velocity_at(2) * 0.35;
            let v01 = velocity_at(1) * 0.05;
            let v = v23 + v12 + v01;

            v.cast::<f32>().cast()
        }
    }
}

/// Touch service.
///
/// # Touch Capture
///
/// Touch capture is integrated with mouse capture in the [`POINTER_CAPTURE`] service.
///
/// # Provider
///
/// This service is provided by the [`TouchManager`] extension.
///
/// [`POINTER_CAPTURE`]: crate::pointer_capture::POINTER_CAPTURE
pub struct TOUCH;

impl TOUCH {
    /// Variable that defines the touch config for the app.
    ///
    /// The value is the same as [`sys_touch_config`], if set the variable disconnects from system config.
    ///
    /// [`sys_touch_config`]: Self::sys_touch_config
    pub fn touch_config(&self) -> ArcCowVar<TouchConfig, ArcVar<TouchConfig>> {
        TOUCH_SV.read().touch_config.clone()
    }

    /// Read-only variable that tracks the system touch config.
    ///
    /// Note that some of these configs are not always used, a tap event for example can happen even if the
    /// touch moves out of the `tap_area` when there is no ambiguity.
    ///
    /// # Value Source
    ///
    /// The value comes from the operating system settings, the variable
    /// updates with a new value if the system setting is changed and on view-process (re)init.
    ///
    /// In headless apps the default is [`TouchConfig::default`] and does not change.
    pub fn sys_touch_config(&self) -> ReadOnlyArcVar<TouchConfig> {
        TOUCH_SV.read().sys_touch_config.read_only()
    }

    /// Variable that tracks all current active touches.
    pub fn positions(&self) -> ReadOnlyArcVar<Vec<TouchPosition>> {
        TOUCH_SV.read().positions.read_only()
    }

    /// Test mode, generates touch events for a single touch contact from raw mouse events.
    ///
    /// Is disabled by default.
    pub fn touch_from_mouse_events(&self) -> ArcVar<bool> {
        TOUCH_SV.read().touch_from_mouse_events.clone()
    }
}

/// Active touch positions.
///
/// Tracked in [`TOUCH.positions`].
///
/// [`TOUCH.positions`]: TOUCH::positions
#[derive(Debug, Clone, PartialEq)]
pub struct TouchPosition {
    /// Touched window.
    pub window_id: WindowId,
    /// Unique ID of the touch, among other active touches.
    pub touch: TouchId,
    /// Latest touch contact position.
    pub position: DipPoint,

    /// Touch start timestamp.
    pub start_time: DInstant,
    /// Latest move timestamp.
    pub update_time: DInstant,
}

app_local! {
    static TOUCH_SV: TouchService = {
        let sys_touch_config = var(TouchConfig::default());
        TouchService {
            touch_config: sys_touch_config.cow(),
            sys_touch_config,
            positions: var(vec![]),
            touch_from_mouse_events: var(false),
        }
    };
}
struct TouchService {
    touch_config: ArcCowVar<TouchConfig, ArcVar<TouchConfig>>,
    sys_touch_config: ArcVar<TouchConfig>,
    positions: ArcVar<Vec<TouchPosition>>,
    touch_from_mouse_events: ArcVar<bool>,
}

/// Identify the moves of one touch contact in [`TouchMoveArgs`].
#[derive(Debug, Clone)]
pub struct TouchMove {
    /// Identify the touch contact or *finger*.
    ///
    /// Multiple points of contact can happen in the same device at the same time,
    /// this ID identifies each uninterrupted contact. IDs are unique only among other concurrent touches
    /// on the same device, after a touch is ended an ID may be reused.
    pub touch: TouchId,

    /// Handle across the lifetime of `touch`.
    ///
    /// See [`TouchInputArgs::touch_propagation`] for more details.
    pub touch_propagation: EventPropagationHandle,

    /// Coalesced moves of the touch since last event.
    ///
    /// Last entry is the latest position.
    pub moves: Vec<(DipPoint, Option<TouchForce>)>,

    /// Velocity in device independent pixels per second.
    ///
    /// The velocity is computed from the 4 non-coalesced move events. If is zero before the fourth event.
    pub velocity: DipVector,

    /// Hit-test result for the latest touch point in the window.
    pub hits: HitTestInfo,

    /// Full path to the top-most hit in [`hits`](TouchMove::hits).
    pub target: InteractionPath,
}
impl TouchMove {
    /// Latest position.
    pub fn position(&self) -> DipPoint {
        self.moves.last().map(|(p, _)| *p).unwrap_or_else(DipPoint::zero)
    }
}

event_args! {
    /// Arguments for [`TOUCH_MOVE_EVENT`].
    pub struct TouchMoveArgs {
        /// Id of window that received all touches in this event.
        pub window_id: WindowId,

        /// Id of device that generated all touches in this event.
        pub device_id: DeviceId,

        /// All touch contacts that moved since last event.
        ///
        /// Note that if a touch contact did not move it will not be in the list, the touch may still be active
        /// however, the [`TOUCH_INPUT_EVENT`] can be used to track touch start and end.
        pub touches: Vec<TouchMove>,

        /// Current pointer capture.
        pub capture: Option<CaptureInfo>,

        /// What modifier keys where pressed when this event happened.
        pub modifiers: ModifiersState,

        ..

        /// Each [`TouchMove::target`] and [`capture`].
        ///
        /// [`capture`]: Self::capture
        fn delivery_list(&self, list: &mut UpdateDeliveryList) {
            for t in &self.touches {
                list.insert_wgt(&t.target);
            }
            if let Some(c) = &self.capture {
                list.insert_wgt(&c.target);
            }
        }
    }

    /// Arguments for [`TOUCH_INPUT_EVENT`].
    pub struct TouchInputArgs {
        /// Id of window that received the event.
        pub window_id: WindowId,

        /// Id of device that generated the event.
        pub device_id: DeviceId,

        /// Identify the touch contact or *finger*.
        ///
        /// Multiple points of contact can happen in the same device at the same time,
        /// this ID identifies each uninterrupted contact. IDs are unique only among other concurrent touches
        /// on the same device, after a touch is ended an ID may be reused.
        pub touch: TouchId,

        /// Propagation handle for the [`touch`] lifetime.
        ///
        /// The [`TOUCH_INPUT_EVENT`] and [`TOUCH_MOVE_EVENT`] have their own separate propagation handles, but
        /// touch gesture events aggregate all these events to produce a single *gesture event*, usually only a single
        /// gesture should be generated, multiple gestures can disambiguate using this `touch_propagation` handle.
        ///
        /// As an example, [`TOUCH_TAP_EVENT`] only tries to match the gesture if it has subscribers, and only notifies
        /// if by the time the gesture completes the `touch_propagation` was not stopped. Touch gesture events or event properties
        /// must stop touch propagation as soon as they commit to a gesture, a *pan* gesture for example, must stop as soon as
        /// it starts scrolling, otherwise the user may accidentally scroll and tap a button at the same time.
        ///
        /// The propagation handle always signals *stopped* after the touch ends. Handles are unique while at least one
        /// clone of it remains, this makes this a better unique identifier of a touch contact than [`TouchId`] that may be reused
        /// by the system as soon as a new touch contact is made.
        ///
        /// [`touch`]: Self::touch
        pub touch_propagation: EventPropagationHandle,

        /// Center of the touch in the window's content area.
        pub position: DipPoint,

        /// Touch pressure force and angle.
        pub force: Option<TouchForce>,

        /// Velocity in device independent pixels per second.
        ///
        /// This is always zero on `Start` and `Cancel` and is the last move velocity for `End`. Note that
        /// the velocity value can be less than [`min_fling_velocity`].
        ///
        /// [`min_fling_velocity`]: TouchConfig::min_fling_velocity
        pub velocity: DipVector,

        /// Touch phase.
        ///
        /// Does not include `Moved`.
        pub phase: TouchPhase,

        /// Hit-test result for the touch point in the window.
        pub hits: HitTestInfo,

        /// Full path to the top-most hit in [`hits`](TouchInputArgs::hits).
        pub target: InteractionPath,

        /// Current pointer capture.
        pub capture: Option<CaptureInfo>,

        /// What modifier keys where pressed when this event happened.
        pub modifiers: ModifiersState,

        ..

        /// The [`target`] and [`capture`].
        ///
        /// [`target`]: Self::target
        /// [`capture`]: Self::capture
        fn delivery_list(&self, list: &mut UpdateDeliveryList) {
            list.insert_wgt(&self.target);
            if let Some(c) = &self.capture {
                list.insert_wgt(&c.target);
            }
        }
    }

    /// Arguments for [`TOUCHED_EVENT`].
    pub struct TouchedArgs {
        /// Id of window that received the event.
        pub window_id: WindowId,

        /// Id of device that generated the event.
        pub device_id: Option<DeviceId>,

        /// Identify the touch contact or *finger*.
        ///
        /// Multiple points of contact can happen in the same device at the same time,
        /// this ID identifies each uninterrupted contact. IDs are unique only among other concurrent touches
        /// on the same device, after a touch is ended an ID may be reused.
        pub touch: TouchId,

        /// Handle across the lifetime of `touch`.
        ///
        /// See [`TouchInputArgs::touch_propagation`] for more details.
        pub touch_propagation: EventPropagationHandle,

        /// Center of the touch in the window's content area.
        pub position: DipPoint,

        /// Touch pressure force and angle.
        pub force: Option<TouchForce>,

        /// Touch phase that caused the contact gain or loss with the widget.
        pub phase: TouchPhase,

        /// Hit-test result for the touch point in the window.
        pub hits: HitTestInfo,

        /// Previous top-most hit before the touch moved.
        pub prev_target: Option<InteractionPath>,

        /// Full path to the top-most hit in [`hits`](TouchInputArgs::hits).
        pub target: Option<InteractionPath>,

        /// Previous pointer capture.
        pub prev_capture: Option<CaptureInfo>,

        /// Current pointer capture.
        pub capture: Option<CaptureInfo>,

        ..

        /// The [`prev_target`], [`target`] and [`capture`].
        ///
        /// [`prev_target`]: Self::prev_target
        /// [`target`]: Self::target
        /// [`capture`]: Self::capture
        fn delivery_list(&self, list: &mut UpdateDeliveryList) {
            if let Some(p) = &self.prev_target {
                list.insert_wgt(p);
            }
            if let Some(p) = &self.target {
                list.insert_wgt(p);
            }
            if let Some(c) = &self.capture {
                list.insert_wgt(&c.target);
            }
        }
    }

    /// Arguments for [`TOUCH_TAP_EVENT`].
    pub struct TouchTapArgs {
        /// Id of window that received the event.
        pub window_id: WindowId,

        /// Id of device that generated the event.
        pub device_id: DeviceId,

        /// Identify the touch contact or *finger*.
        ///
        /// Multiple points of contact can happen in the same device at the same time,
        /// this ID identifies each uninterrupted contact. IDs are unique only among other concurrent touches
        /// on the same device, after a touch is ended an ID may be reused.
        pub touch: TouchId,

        /// Center of the touch in the window's content area.
        pub position: DipPoint,

        /// Hit-test result for the touch point in the window.
        pub hits: HitTestInfo,

        /// Full path to the top-most hit in [`hits`](TouchInputArgs::hits).
        pub target: InteractionPath,

        /// What modifier keys where pressed when this event happened.
        pub modifiers: ModifiersState,

        /// Count of taps within the double-tap interval. Number `1` is single tap, `2` is double tap, etc.
        pub tap_count: NonZeroU32,

        ..

        /// The [`target`].
        ///
        /// [`target`]: Self::target
        fn delivery_list(&self, list: &mut UpdateDeliveryList) {
            list.insert_wgt(&self.target);
        }
    }

    /// Arguments for [`TOUCH_LONG_PRESS_EVENT`].
    pub struct TouchLongPressArgs {
        /// Id of window that received the event.
        pub window_id: WindowId,

        /// Id of device that generated the event.
        pub device_id: DeviceId,

        /// Identify the touch contact or *finger*.
        ///
        /// Multiple points of contact can happen in the same device at the same time,
        /// this ID identifies each uninterrupted contact. IDs are unique only among other concurrent touches
        /// on the same device, after a touch is ended an ID may be reused.
        pub touch: TouchId,

        /// Center of the touch in the window's content area.
        pub position: DipPoint,

        /// Hit-test result for the touch point in the window.
        pub hits: HitTestInfo,

        /// Full path to the top-most hit in [`hits`](TouchInputArgs::hits).
        pub target: InteractionPath,

        /// What modifier keys where pressed when this touch started.
        pub modifiers: ModifiersState,

        /// Timestamp of when the touch started.
        pub start_time: DInstant,

        ..

        /// The [`target`].
        ///
        /// [`target`]: Self::target
        fn delivery_list(&self, list: &mut UpdateDeliveryList) {
            list.insert_wgt(&self.target);
        }
    }

    /// Arguments for [`TOUCH_TRANSFORM_EVENT`].
    pub struct TouchTransformArgs {
        /// Id of window that received the touch events.
        pub window_id: WindowId,

        /// Id of the device that generated the touch events.
        pub device_id: DeviceId,

        /// Info collected when the second touch point started.
        pub first_info: TouchTransformInfo,

        /// Latest update of the two points.
        pub latest_info: TouchTransformInfo,

        /// Velocity of the `latest_info` touch points.
        pub velocity: [PxVector; 2],

        /// Scale factor used in the computed pixel values.
        ///
        /// This is the window's scale factor when the first touch started.
        pub scale_factor: Factor,

        /// Gesture phase.
        pub phase: TouchPhase,

        /// Hit-test result for the center point between the first position of the two touches in the window
        /// when the gesture started.
        pub hits: HitTestInfo,

        /// Full path to the top-most hit in [`hits`](TouchInputArgs::hits).
        pub target: InteractionPath,

        /// Current pointer capture.
        pub capture: Option<CaptureInfo>,

        /// What modifier keys where pressed when this event happened.
        pub modifiers: ModifiersState,

        ..

        /// The [`target`] and [`capture`].
        ///
        /// [`target`]: Self::target
        /// [`capture`]: Self::capture
        fn delivery_list(&self, list: &mut UpdateDeliveryList) {
            list.insert_wgt(&self.target);
            if let Some(c) = &self.capture {
                list.insert_wgt(&c.target);
            }
        }
    }
}

impl TouchMoveArgs {
    /// If [`capture`] is `None` or [`allows`] the [`WIDGET`] to receive this event.
    ///
    /// [`capture`]: Self::capture
    /// [`allows`]: CaptureInfo::allows
    /// [`WIDGET`]: zng_app::widget::WIDGET
    pub fn capture_allows(&self) -> bool {
        self.capture.as_ref().map(|c| c.allows()).unwrap_or(true)
    }
}

impl TouchInputArgs {
    /// If [`capture`] is `None` or [`allows`] the [`WIDGET`] to receive this event.
    ///
    /// [`capture`]: Self::capture
    /// [`allows`]: CaptureInfo::allows
    /// [`WIDGET`]: zng_app::widget::WIDGET
    pub fn capture_allows(&self) -> bool {
        self.capture.as_ref().map(|c| c.allows()).unwrap_or(true)
    }

    /// If the `widget_id` is in the [`target`] is enabled.
    ///
    /// [`target`]: Self::target
    pub fn is_enabled(&self, widget_id: WidgetId) -> bool {
        self.target.interactivity_of(widget_id).map(|i| i.is_enabled()).unwrap_or(false)
    }

    /// If the `widget_id` is in the [`target`] is disabled.
    ///
    /// [`target`]: Self::target
    pub fn is_disabled(&self, widget_id: WidgetId) -> bool {
        self.target.interactivity_of(widget_id).map(|i| i.is_disabled()).unwrap_or(false)
    }

    /// If the [`phase`] is start.
    ///
    /// [`phase`]: Self::phase
    pub fn is_touch_start(&self) -> bool {
        matches!(self.phase, TouchPhase::Start)
    }

    /// If the [`phase`] is end.
    ///
    /// [`phase`]: Self::phase
    pub fn is_touch_end(&self) -> bool {
        matches!(self.phase, TouchPhase::End)
    }

    /// If the [`phase`] is cancel.
    ///
    /// [`phase`]: Self::phase
    pub fn is_touch_cancel(&self) -> bool {
        matches!(self.phase, TouchPhase::Cancel)
    }

    /// Compute the final offset and duration for a *fling* animation that simulates inertia movement from the
    /// [`velocity.x`] and `friction`. Returns 0 if velocity less than [`min_fling_velocity`].
    ///
    /// Friction is in dips decelerated per second.
    ///
    /// To animate a point using these values:
    ///
    /// * Compute the final point by adding the vector offset to the current point.
    /// * Animate using the duration linear interpolation.
    ///
    /// [`velocity.x`]: Self::velocity
    /// [`min_fling_velocity`]: TouchConfig::min_fling_velocity
    pub fn inertia_x(&self, friction: Dip) -> (Dip, Duration) {
        Self::inertia(self.velocity.x, friction)
    }

    /// Compute the final offset and duration for a *fling* animation that simulates inertia movement from the
    /// [`velocity.y`] and `friction`. Returns 0 if velocity less than [`min_fling_velocity`].
    ///
    /// Friction is in dips decelerated per second.
    ///
    /// [`velocity.y`]: Self::velocity
    /// [`min_fling_velocity`]: TouchConfig::min_fling_velocity
    pub fn inertia_y(&self, friction: Dip) -> (Dip, Duration) {
        Self::inertia(self.velocity.y, friction)
    }

    fn inertia(velocity: Dip, friction: Dip) -> (Dip, Duration) {
        let cfg = TOUCH.touch_config().get();
        let signal = if velocity >= 0 { 1.0 } else { -1.0 };
        let velocity = velocity.abs();

        if velocity < cfg.min_fling_velocity {
            (Dip::new(0), Duration::ZERO)
        } else {
            let velocity = velocity.min(cfg.max_fling_velocity).to_f32();
            let friction = friction.to_f32();

            let time = velocity / friction;
            let offset = (velocity * time) - (friction * time);

            (Dip::from(offset) * signal, time.secs())
        }
    }
}

impl TouchTapArgs {
    /// If the `widget_id` is in the [`target`] is enabled.
    ///
    /// [`target`]: Self::target
    pub fn is_enabled(&self, widget_id: WidgetId) -> bool {
        self.target.interactivity_of(widget_id).map(|i| i.is_enabled()).unwrap_or(false)
    }

    /// If the `widget_id` is in the [`target`] is disabled.
    ///
    /// [`target`]: Self::target
    pub fn is_disabled(&self, widget_id: WidgetId) -> bool {
        self.target.interactivity_of(widget_id).map(|i| i.is_disabled()).unwrap_or(false)
    }
}

impl TouchLongPressArgs {
    /// If the `widget_id` is in the [`target`] is enabled.
    ///
    /// [`target`]: Self::target
    pub fn is_enabled(&self, widget_id: WidgetId) -> bool {
        self.target.interactivity_of(widget_id).map(|i| i.is_enabled()).unwrap_or(false)
    }

    /// If the `widget_id` is in the [`target`] is disabled.
    ///
    /// [`target`]: Self::target
    pub fn is_disabled(&self, widget_id: WidgetId) -> bool {
        self.target.interactivity_of(widget_id).map(|i| i.is_disabled()).unwrap_or(false)
    }
}

impl TouchedArgs {
    /// If [`capture`] is `None` or [`allows`] the [`WIDGET`] to receive this event.
    ///
    /// [`capture`]: Self::capture
    /// [`allows`]: CaptureInfo::allows
    /// [`WIDGET`]: zng_app::widget::WIDGET
    pub fn capture_allows(&self) -> bool {
        self.capture.as_ref().map(|c| c.allows()).unwrap_or(true)
    }

    /// Event caused by the touch position moving over/out of the widget bounds.
    pub fn is_touch_move(&self) -> bool {
        self.device_id.is_some()
    }

    /// Event caused by the widget moving under/out of the mouse position.
    pub fn is_widget_move(&self) -> bool {
        self.device_id.is_none()
    }

    /// Event caused by a pointer capture change.
    pub fn is_capture_change(&self) -> bool {
        self.prev_capture != self.capture
    }

    /// Returns `true` if the [`WIDGET`] was not touched, but now is.
    ///
    /// [`WIDGET`]: zng_app::widget::WIDGET
    pub fn is_touch_enter(&self) -> bool {
        !self.was_touched() && self.is_touched()
    }

    /// Returns `true` if the [`WIDGET`] was touched, but now isn't.
    ///
    /// [`WIDGET`]: zng_app::widget::WIDGET
    pub fn is_touch_leave(&self) -> bool {
        self.was_touched() && !self.is_touched()
    }

    /// Returns `true` if the [`WIDGET`] was not touched or was disabled, but now is touched and enabled.
    ///
    /// [`WIDGET`]: zng_app::widget::WIDGET
    pub fn is_touch_enter_enabled(&self) -> bool {
        (!self.was_touched() || self.was_disabled(WIDGET.id())) && self.is_touched() && self.is_enabled(WIDGET.id())
    }

    /// Returns `true` if the [`WIDGET`] was touched and enabled, but now is not touched or is disabled.
    ///
    /// [`WIDGET`]: zng_app::widget::WIDGET
    pub fn is_touch_leave_enabled(&self) -> bool {
        self.was_touched() && self.was_enabled(WIDGET.id()) && (!self.is_touched() || self.is_disabled(WIDGET.id()))
    }

    /// Returns `true` if the [`WIDGET`] was not touched or was enabled, but now is touched and disabled.
    ///
    /// [`WIDGET`]: zng_app::widget::WIDGET
    pub fn is_touch_enter_disabled(&self) -> bool {
        (!self.was_touched() || self.was_enabled(WIDGET.id())) && self.is_touched() && self.is_disabled(WIDGET.id())
    }

    /// Returns `true` if the [`WIDGET`] was touched and disabled, but now is not touched or is enabled.
    ///
    /// [`WIDGET`]: zng_app::widget::WIDGET
    pub fn is_touch_leave_disabled(&self) -> bool {
        self.was_touched() && self.was_disabled(WIDGET.id()) && (!self.is_touched() || self.is_enabled(WIDGET.id()))
    }

    /// Returns `true` if the [`WIDGET`] is in [`prev_target`] and is allowed by the [`prev_capture`].
    ///
    /// [`prev_target`]: Self::prev_target
    /// [`prev_capture`]: Self::prev_capture
    /// [`WIDGET`]: zng_app::widget::WIDGET
    pub fn was_touched(&self) -> bool {
        if let Some(cap) = &self.prev_capture {
            if !cap.allows() {
                return false;
            }
        }

        if let Some(t) = &self.prev_target {
            return t.contains(WIDGET.id());
        }

        false
    }

    /// Returns `true` if the [`WIDGET`] is in [`target`] and is allowed by the current [`capture`].
    ///
    /// [`target`]: Self::target
    /// [`capture`]: Self::capture
    /// [`WIDGET`]: zng_app::widget::WIDGET
    pub fn is_touched(&self) -> bool {
        if let Some(cap) = &self.capture {
            if !cap.allows() {
                return false;
            }
        }

        if let Some(t) = &self.target {
            return t.contains(WIDGET.id());
        }

        false
    }

    /// Returns `true` if the widget was enabled in [`prev_target`].
    ///
    /// [`prev_target`]: Self::prev_target
    pub fn was_enabled(&self, widget_id: WidgetId) -> bool {
        self.prev_target
            .as_ref()
            .and_then(|t| t.interactivity_of(widget_id))
            .map(|itr| itr.is_enabled())
            .unwrap_or(false)
    }

    /// Returns `true` if the widget was disabled in [`prev_target`].
    ///
    /// [`prev_target`]: Self::prev_target
    pub fn was_disabled(&self, widget_id: WidgetId) -> bool {
        self.prev_target
            .as_ref()
            .and_then(|t| t.interactivity_of(widget_id))
            .map(|itr| itr.is_disabled())
            .unwrap_or(false)
    }

    /// Returns `true` if the widget is enabled in [`target`].
    ///
    /// [`target`]: Self::target
    pub fn is_enabled(&self, widget_id: WidgetId) -> bool {
        self.target
            .as_ref()
            .and_then(|t| t.interactivity_of(widget_id))
            .map(|itr| itr.is_enabled())
            .unwrap_or(false)
    }

    /// Returns `true` if the widget is disabled in [`target`].
    ///
    /// [`target`]: Self::target
    pub fn is_disabled(&self, widget_id: WidgetId) -> bool {
        self.target
            .as_ref()
            .and_then(|t| t.interactivity_of(widget_id))
            .map(|itr| itr.is_disabled())
            .unwrap_or(false)
    }
}

impl TouchTransformArgs {
    /// If [`capture`] is `None` or [`allows`] the [`WIDGET`] to receive this event.
    ///
    /// [`capture`]: Self::capture
    /// [`allows`]: CaptureInfo::allows
    /// [`WIDGET`]: zng_app::widget::WIDGET
    pub fn capture_allows(&self) -> bool {
        self.capture.as_ref().map(|c| c.allows()).unwrap_or(true)
    }

    /// If the `widget_id` is in the [`target`] is enabled.
    ///
    /// [`target`]: Self::target
    pub fn is_enabled(&self, widget_id: WidgetId) -> bool {
        self.target.interactivity_of(widget_id).map(|i| i.is_enabled()).unwrap_or(false)
    }

    /// If the `widget_id` is in the [`target`] is disabled.
    ///
    /// [`target`]: Self::target
    pub fn is_disabled(&self, widget_id: WidgetId) -> bool {
        self.target.interactivity_of(widget_id).map(|i| i.is_disabled()).unwrap_or(false)
    }

    /// Gets the [`first_info`] and [`latest_info`] in the [`WIDGET`] inner bounds space.
    ///
    /// [`first_info`]: Self::first_info
    /// [`latest_info`]: Self::latest_info
    /// [`WIDGET`]: zng_app::widget::WIDGET
    pub fn local_info(&self) -> [TouchTransformInfo; 2] {
        let mut first = self.first_info.clone();
        let mut latest = self.latest_info.clone();

        let offset = WIDGET.bounds().inner_offset();

        first -= offset;
        latest -= offset;

        [first, latest]
    }

    /// Computes the translation to transform from [`first_info`] to [`latest_info`].
    ///
    /// [`first_info`]: Self::first_info
    /// [`latest_info`]: Self::latest_info
    pub fn translation(&self) -> euclid::Vector2D<f32, Px> {
        self.first_info.translation(&self.latest_info)
    }

    /// Computes the translation-x to transform from [`first_info`] to [`latest_info`].
    ///
    /// [`first_info`]: Self::first_info
    /// [`latest_info`]: Self::latest_info
    pub fn translation_x(&self) -> f32 {
        self.first_info.translation_x(&self.latest_info)
    }

    /// Computes the translation-y to transform from [`first_info`] to [`latest_info`].
    ///
    /// [`first_info`]: Self::first_info
    /// [`latest_info`]: Self::latest_info
    pub fn translation_y(&self) -> f32 {
        self.first_info.translation_y(&self.latest_info)
    }

    /// Computes the rotation to transform from [`first_info`] to [`latest_info`].
    ///
    /// [`first_info`]: Self::first_info
    /// [`latest_info`]: Self::latest_info
    pub fn rotation(&self) -> AngleRadian {
        self.first_info.rotation(&self.latest_info)
    }

    /// Computes the scale to transform from [`first_info`] to [`latest_info`].
    ///
    /// [`first_info`]: Self::first_info
    /// [`latest_info`]: Self::latest_info
    pub fn scale(&self) -> Factor {
        self.first_info.scale(&self.latest_info)
    }

    /// Computes the scale-y to transform from [`first_info`] to [`latest_info`].
    ///
    /// [`first_info`]: Self::first_info
    /// [`latest_info`]: Self::latest_info
    pub fn scale_x(&self) -> Factor {
        self.first_info.scale_x(&self.latest_info)
    }

    /// Computes the scale-y to transform from [`first_info`] to [`latest_info`].
    ///
    /// [`first_info`]: Self::first_info
    /// [`latest_info`]: Self::latest_info
    pub fn scale_y(&self) -> Factor {
        self.first_info.scale_y(&self.latest_info)
    }

    /// Computes the transform from [`first_info`] to [`latest_info`].
    ///
    /// [`first_info`]: Self::first_info
    /// [`latest_info`]: Self::latest_info
    pub fn transform(&self, mode: TouchTransformMode) -> PxTransform {
        self.first_info.transform(&self.latest_info, mode)
    }

    /// Computes the transform between the [`local_info`] values, rotates and scales around the latest center.
    ///
    /// [`local_info`]: Self::local_info
    pub fn local_transform(&self, mode: TouchTransformMode) -> PxTransform {
        let [first, latest] = self.local_info();

        let mut r = first.transform(&latest, mode);

        if mode.contains(TouchTransformMode::ROTATE)
            || mode.contains(TouchTransformMode::SCALE_X)
            || mode.contains(TouchTransformMode::SCALE_Y)
        {
            let c = latest.center.to_vector();
            r = PxTransform::Offset(-c).then(&r).then_translate(c);
        }

        r
    }

    /// Average velocity.
    pub fn translation_velocity(&self) -> PxVector {
        (self.velocity[0] + self.velocity[1]) / Px(2)
    }

    /// Compute the final offset and duration for a *fling* animation that simulates inertia movement from the
    /// [`translation_velocity().x`] and `deceleration`. Returns 0 if velocity less than [`min_fling_velocity`].
    ///
    /// Deceleration is in dip/s, a good value is 1000. The recommended animation easing function
    /// is `|t| easing::ease_out(easing::quad, t)`.
    ///
    /// [`translation_velocity().x`]: Self::translation_velocity
    /// [`min_fling_velocity`]: TouchConfig::min_fling_velocity
    pub fn translation_inertia_x(&self, deceleration: Dip) -> (Px, Duration) {
        self.inertia((self.velocity[0].x + self.velocity[1].x) / Px(2), deceleration)
    }

    /// Compute the final offset and duration for a *fling* animation that simulates inertia movement from the
    /// [`translation_velocity().y`] and `deceleration`. Returns 0 if velocity less than [`min_fling_velocity`].
    ///
    /// Deceleration is in dip/s, a good value is 1000. The recommended animation easing function is
    /// `|t| easing::ease_out(easing::quad, t)`.
    ///
    /// [`translation_velocity().y`]: Self::translation_velocity
    /// [`min_fling_velocity`]: TouchConfig::min_fling_velocity
    pub fn translation_inertia_y(&self, deceleration: Dip) -> (Px, Duration) {
        self.inertia((self.velocity[0].y + self.velocity[1].y) / Px(2), deceleration)
    }

    /// If the [`phase`] is start.
    ///
    /// Note that the [`latest_info`] may already be different from [`first_info`] if the gesture
    /// detector awaited to disambiguate before starting the gesture.
    ///
    /// [`phase`]: Self::phase
    /// [`first_info`]: Self::first_info
    /// [`latest_info`]: Self::latest_info
    pub fn is_start(&self) -> bool {
        matches!(self.phase, TouchPhase::Start)
    }

    /// If the [`phase`] is end.
    ///
    /// Any transform already applied must be committed.
    ///
    /// [`phase`]: Self::phase
    pub fn is_end(&self) -> bool {
        matches!(self.phase, TouchPhase::End)
    }

    /// If the [`phase`] is cancel.
    ///
    /// Any transform already applied must be undone.
    ///
    /// [`phase`]: Self::phase
    pub fn is_cancel(&self) -> bool {
        matches!(self.phase, TouchPhase::Cancel)
    }

    fn inertia(&self, velocity: Px, deceleration: Dip) -> (Px, Duration) {
        let friction = deceleration.to_px(self.scale_factor);
        let cfg = TOUCH.touch_config().get();
        let min_fling_velocity = cfg.min_fling_velocity.to_px(self.scale_factor);

        let signal = if velocity >= 0 { 1.0 } else { -1.0 };
        let velocity = velocity.abs();

        if velocity < min_fling_velocity {
            (Px(0), Duration::ZERO)
        } else {
            let max_fling_velocity = cfg.max_fling_velocity.to_px(self.scale_factor);
            let velocity = velocity.min(max_fling_velocity).0 as f32;
            let friction = friction.0 as f32;

            let time = velocity / friction;
            let offset = 0.5 * friction * time * time;
            (Px(offset.round() as _) * signal, time.secs())
        }
    }
}

event! {
    /// Touch contact moved.
    pub static TOUCH_MOVE_EVENT: TouchMoveArgs;

    /// Touch contact started or ended.
    pub static TOUCH_INPUT_EVENT: TouchInputArgs;

    /// Touch made first contact or lost contact with a widget.
    pub static TOUCHED_EVENT: TouchedArgs;

    /// Touch tap.
    ///
    /// This is a touch gesture event, it only notifies if it has listeners, either widget subscribers in the
    /// touched path or app level hooks.
    pub static TOUCH_TAP_EVENT: TouchTapArgs;

    /// Two point touch transform.
    ///
    /// This is a touch gesture event, it only notifies if it has listeners, either widget subscribers in the
    /// touched path or app level hooks.
    pub static TOUCH_TRANSFORM_EVENT: TouchTransformArgs;

    /// Touch contact pressed without moving for more then the [`tap_max_time`].
    ///
    /// This is a touch gesture event, it only notifies if it has listeners, either widget subscribers in the
    /// touched path or app level hooks.
    ///
    /// [`tap_max_time`]: TouchConfig::tap_max_time
    pub static TOUCH_LONG_PRESS_EVENT: TouchLongPressArgs;
}

impl AppExtension for TouchManager {
    fn event_preview(&mut self, update: &mut EventUpdate) {
        if let Some(args) = RAW_FRAME_RENDERED_EVENT.on(update) {
            self.continue_pressed(args.window_id);
        } else if let Some(args) = RAW_TOUCH_EVENT.on(update) {
            let mut pending_move: Vec<TouchMove> = vec![];

            for u in &args.touches {
                if let TouchPhase::Move = u.phase {
                    if let Some(e) = pending_move.iter_mut().find(|e| e.touch == u.touch) {
                        e.moves.push((u.position, u.force));
                    } else {
                        pending_move.push(TouchMove {
                            touch: u.touch,
                            touch_propagation: if let Some(i) = self.pressed.get(&u.touch) {
                                i.touch_propagation.clone()
                            } else {
                                let weird = EventPropagationHandle::new();
                                weird.stop();
                                weird
                            },
                            moves: vec![(u.position, u.force)],
                            velocity: DipVector::zero(),
                            hits: HitTestInfo::no_hits(args.window_id), // hit-test deferred
                            target: InteractionPath::new(args.window_id, []),
                        });
                    }
                } else {
                    self.on_move(args, mem::take(&mut pending_move));
                    self.on_input(args, u);
                }
            }

            self.on_move(args, pending_move);
        } else if let Some(args) = WIDGET_INFO_CHANGED_EVENT.on(update) {
            self.continue_pressed(args.window_id);
        } else if let Some(args) = MODIFIERS_CHANGED_EVENT.on(update) {
            self.modifiers = args.modifiers;
        } else if let Some(args) = RAW_TOUCH_CONFIG_CHANGED_EVENT.on(update) {
            TOUCH_SV.read().touch_config.set(args.config);
        } else if let Some(args) = VIEW_PROCESS_INITED_EVENT.on(update) {
            TOUCH_SV.read().touch_config.set(args.touch_config);

            if args.is_respawn {
                self.tap_gesture.clear();
                self.transform_gesture.clear();
                self.long_press_gesture.clear();
                TOUCH_SV.read().positions.set(vec![]);

                for (touch, info) in self.pressed.drain() {
                    let args = TouchInputArgs::now(
                        info.target.window_id(),
                        info.device_id,
                        touch,
                        info.touch_propagation.clone(),
                        DipPoint::splat(Dip::new(-1)),
                        None,
                        DipVector::zero(),
                        TouchPhase::Cancel,
                        HitTestInfo::no_hits(info.target.window_id()),
                        info.target.clone(),
                        None,
                        ModifiersState::empty(),
                    );
                    TOUCH_INPUT_EVENT.notify(args);

                    let args = TouchedArgs::now(
                        info.target.window_id(),
                        info.device_id,
                        touch,
                        info.touch_propagation,
                        DipPoint::splat(Dip::new(-1)),
                        None,
                        TouchPhase::Cancel,
                        HitTestInfo::no_hits(info.target.window_id()),
                        info.target,
                        None,
                        None,
                        None,
                    );
                    TOUCHED_EVENT.notify(args);
                }
            }
        } else if TOUCH_SV.read().touch_from_mouse_events.get() {
            use super::mouse::*;

            if let Some(args) = MOUSE_MOVE_EVENT.on(update) {
                if let Some(id) = self.mouse_touch {
                    args.propagation().stop();

                    RAW_TOUCH_EVENT.notify(RawTouchArgs::now(
                        args.window_id,
                        args.device_id,
                        vec![TouchUpdate {
                            touch: id,
                            phase: TouchPhase::Move,
                            position: args.position,
                            force: None,
                        }],
                    ));
                }
            } else if let Some(args) = MOUSE_INPUT_EVENT.on(update) {
                if args.button == super::mouse::MouseButton::Left {
                    args.propagation().stop();

                    let phase = match args.state {
                        ButtonState::Pressed => {
                            if self.mouse_touch.is_some() {
                                return;
                            }
                            self.mouse_touch = Some(TouchId(u64::MAX));
                            TouchPhase::Start
                        }
                        ButtonState::Released => {
                            if self.mouse_touch.is_none() {
                                return;
                            }
                            self.mouse_touch = None;
                            TouchPhase::End
                        }
                    };

                    RAW_TOUCH_EVENT.notify(RawTouchArgs::now(
                        args.window_id,
                        args.device_id.unwrap_or(DeviceId::new_unique()),
                        vec![TouchUpdate {
                            touch: TouchId(u64::MAX),
                            phase,
                            position: args.position,
                            force: None,
                        }],
                    ));
                }
            } else if let Some(args) = RAW_MOUSE_LEFT_EVENT.on(update) {
                if let Some(id) = self.mouse_touch.take() {
                    RAW_TOUCH_EVENT.notify(RawTouchArgs::now(
                        args.window_id,
                        args.device_id,
                        vec![TouchUpdate {
                            touch: id,
                            phase: TouchPhase::Cancel,
                            position: DipPoint::zero(),
                            force: None,
                        }],
                    ))
                }
            }
        }
    }

    fn event(&mut self, update: &mut EventUpdate) {
        if let Some(args) = TOUCH_INPUT_EVENT.on(update) {
            self.tap_gesture.on_input(args);
            self.transform_gesture.on_input(args);
            self.long_press_gesture.on_input(args);
        } else if let Some(args) = TOUCH_MOVE_EVENT.on(update) {
            self.tap_gesture.on_move(args);
            self.transform_gesture.on_move(args);
            self.long_press_gesture.on_move(args);
        } else if let Some(args) = POINTER_CAPTURE_EVENT.on(update) {
            for (touch, info) in &self.pressed {
                let args = TouchedArgs::now(
                    info.target.window_id(),
                    info.device_id,
                    *touch,
                    info.touch_propagation.clone(),
                    info.position,
                    info.force,
                    TouchPhase::Move,
                    info.hits.clone(),
                    info.target.clone(),
                    info.target.clone(),
                    args.prev_capture.clone(),
                    args.new_capture.clone(),
                );
                TOUCHED_EVENT.notify(args);
            }
        }
    }

    fn update_preview(&mut self) {
        self.long_press_gesture.on_update();
    }
}
impl TouchManager {
    fn on_input(&mut self, args: &RawTouchArgs, update: &TouchUpdate) {
        if let Ok(w) = WINDOWS.widget_tree(args.window_id) {
            let mut hits = w.root().hit_test(update.position.to_px(w.scale_factor()));
            let mut target = hits
                .target()
                .and_then(|t| w.get(t.widget_id))
                .map(|t| t.interaction_path())
                .unwrap_or_else(|| w.root().interaction_path());
            let mut position = update.position;

            // hit-test for nested windows
            if let Some(wgt) = w.get(target.widget_id()) {
                if let Some(w) = wgt.nested_window_tree() {
                    let f = w.scale_factor();
                    let p = update.position.to_px(f);
                    let p = wgt.inner_transform().inverse().and_then(|t| t.transform_point(p)).unwrap_or(p);
                    position = p.to_dip(f);
                    hits = w.root().hit_test(p);
                    target = hits
                        .target()
                        .and_then(|t| w.get(t.widget_id))
                        .map(|t| t.interaction_path())
                        .unwrap_or_else(|| w.root().interaction_path());
                }
            }

            let target = match target.unblocked() {
                Some(t) => t,
                None => return, // entire window blocked
            };

            let capture_info = POINTER_CAPTURE.current_capture_value();

            let (gesture_handle, velocity) = match update.phase {
                TouchPhase::Start => {
                    let handle = EventPropagationHandle::new();
                    if let Some(weird) = self.pressed.insert(
                        update.touch,
                        PressedInfo {
                            touch_propagation: handle.clone(),
                            target: target.clone(),
                            device_id: args.device_id,
                            position,
                            force: update.force,
                            hits: hits.clone(),
                            velocity_samples: vec![], // skip input (will only have velocity after 4 moves)
                        },
                    ) {
                        weird.touch_propagation.stop();
                    }
                    (handle, DipVector::zero())
                }
                TouchPhase::End => {
                    if let Some(handle) = self.pressed.remove(&update.touch) {
                        let vel = handle.velocity();
                        (handle.touch_propagation, vel)
                    } else {
                        let weird = EventPropagationHandle::new();
                        weird.stop();
                        (weird, DipVector::zero())
                    }
                }
                TouchPhase::Cancel => {
                    let handle = self.pressed.remove(&update.touch).map(|i| i.touch_propagation).unwrap_or_default();
                    handle.stop();
                    (handle, DipVector::zero())
                }
                TouchPhase::Move => unreachable!(),
            };

            match update.phase {
                TouchPhase::Start => {
                    let pos_info = TouchPosition {
                        window_id: hits.window_id(),
                        touch: update.touch,
                        position,
                        start_time: args.timestamp,
                        update_time: args.timestamp,
                    };
                    TOUCH_SV.read().positions.modify(move |p| {
                        let p = p.to_mut();
                        if let Some(weird) = p.iter().position(|p| p.touch == pos_info.touch) {
                            p.remove(weird);
                        }
                        p.push(pos_info);
                    });
                }
                _ => {
                    let touch = update.touch;
                    TOUCH_SV.read().positions.modify(move |p| {
                        if let Some(i) = p.iter().position(|p| p.touch == touch) {
                            p.to_mut().remove(i);
                        }
                    });
                }
            }

            let args = TouchInputArgs::now(
                hits.window_id(),
                args.device_id,
                update.touch,
                gesture_handle,
                position,
                update.force,
                velocity,
                update.phase,
                hits,
                target,
                capture_info,
                self.modifiers,
            );

            let touched_args = {
                // touched

                let (prev_target, target) = match args.phase {
                    TouchPhase::Start => (None, Some(args.target.clone())),
                    TouchPhase::End | TouchPhase::Cancel => (Some(args.target.clone()), None),
                    TouchPhase::Move => unreachable!(),
                };

                TouchedArgs::now(
                    args.window_id,
                    args.device_id,
                    args.touch,
                    args.touch_propagation.clone(),
                    args.position,
                    args.force,
                    args.phase,
                    args.hits.clone(),
                    prev_target,
                    target,
                    args.capture.clone(),
                    args.capture.clone(),
                )
            };

            TOUCH_INPUT_EVENT.notify(args);
            TOUCHED_EVENT.notify(touched_args);
        } else {
            // did not find window, cleanup touched
            for u in &args.touches {
                if let Some(i) = self.pressed.remove(&u.touch) {
                    let capture = POINTER_CAPTURE.current_capture_value();
                    let args = TouchedArgs::now(
                        args.window_id,
                        args.device_id,
                        u.touch,
                        i.touch_propagation,
                        u.position,
                        u.force,
                        u.phase,
                        HitTestInfo::no_hits(args.window_id),
                        Some(i.target),
                        None,
                        capture.clone(),
                        capture,
                    );
                    TOUCHED_EVENT.notify(args);
                }
            }
        }
    }

    fn on_move(&mut self, args: &RawTouchArgs, mut moves: Vec<TouchMove>) {
        if !moves.is_empty() {
            if let Ok(w) = WINDOWS.widget_tree(args.window_id) {
                let mut window_blocked_remove = vec![];
                for m in &mut moves {
                    m.hits = w.root().hit_test(m.position().to_px(w.scale_factor()));
                    let target = m
                        .hits
                        .target()
                        .and_then(|t| w.get(t.widget_id))
                        .map(|t| t.interaction_path())
                        .unwrap_or_else(|| w.root().interaction_path());

                    match target.unblocked() {
                        Some(t) => {
                            m.target = t;
                            // hit-test for nested windows
                            if let Some(wgt) = w.get(m.target.widget_id()) {
                                if let Some(w) = wgt.nested_window_tree() {
                                    let transform = wgt.inner_transform().inverse();
                                    let factor = w.scale_factor();
                                    let mut position = PxPoint::zero(); // last
                                    for (mv, _) in &mut m.moves {
                                        let p = mv.to_px(factor);
                                        let p = transform.and_then(|t| t.transform_point(p)).unwrap_or(p);
                                        *mv = p.to_dip(factor);
                                        position = p;
                                    }
                                    m.hits = w.root().hit_test(position);
                                    let target = m
                                        .hits
                                        .target()
                                        .and_then(|t| w.get(t.widget_id))
                                        .map(|t| t.interaction_path())
                                        .unwrap_or_else(|| w.root().interaction_path());

                                    match target.unblocked() {
                                        Some(t) => m.target = t,
                                        None => window_blocked_remove.push(m.touch),
                                    }
                                }
                            }
                        }
                        None => {
                            window_blocked_remove.push(m.touch);
                        }
                    }
                }

                let position_updates: Vec<_> = moves
                    .iter()
                    .map(|m| TouchPosition {
                        window_id: args.window_id,
                        touch: m.touch,
                        position: m.position(),
                        start_time: args.timestamp, // ignored
                        update_time: args.timestamp,
                    })
                    .collect();
                TOUCH_SV.read().positions.modify(move |p| {
                    for mut update in position_updates {
                        if let Some(i) = p.iter().position(|p| p.touch == update.touch) {
                            update.start_time = p[i].start_time;
                            p.to_mut()[i] = update;
                        }
                    }
                });

                let capture_info = POINTER_CAPTURE.current_capture_value();

                let mut touched_events = vec![];

                for touch in window_blocked_remove {
                    let touch_move = moves.iter().position(|t| t.touch == touch).unwrap();
                    moves.swap_remove(touch_move);

                    if let Some(i) = self.pressed.remove(&touch) {
                        i.touch_propagation.stop();
                        let args = TouchedArgs::now(
                            args.window_id,
                            args.device_id,
                            touch,
                            i.touch_propagation,
                            DipPoint::splat(Dip::new(-1)),
                            None,
                            TouchPhase::Cancel,
                            HitTestInfo::no_hits(args.window_id),
                            i.target,
                            None,
                            None,
                            None,
                        );
                        touched_events.push(args);
                    }
                }
                for m in &mut moves {
                    if let Some(i) = self.pressed.get_mut(&m.touch) {
                        let (position, force) = *m.moves.last().unwrap();
                        i.push_velocity_sample(args.timestamp, position);
                        m.velocity = i.velocity();
                        i.position = position;
                        i.force = force;
                        i.hits = m.hits.clone();
                        if i.target != m.target {
                            let args = TouchedArgs::now(
                                args.window_id,
                                args.device_id,
                                m.touch,
                                m.touch_propagation.clone(),
                                position,
                                force,
                                TouchPhase::Move,
                                m.hits.clone(),
                                i.target.clone(),
                                m.target.clone(),
                                capture_info.clone(),
                                capture_info.clone(),
                            );
                            i.target = m.target.clone();
                            touched_events.push(args);
                        }
                    }
                }

                if !moves.is_empty() {
                    let args = TouchMoveArgs::now(args.window_id, args.device_id, moves, capture_info, self.modifiers);
                    TOUCH_MOVE_EVENT.notify(args);
                }

                for args in touched_events {
                    TOUCHED_EVENT.notify(args);
                }
            }
        }
    }

    fn continue_pressed(&mut self, window_id: WindowId) {
        let mut tree = None;

        let mut window_blocked_remove = vec![];

        for (touch, info) in &mut self.pressed {
            if info.target.window_id() != window_id {
                continue;
            }

            let tree = tree.get_or_insert_with(|| WINDOWS.widget_tree(window_id).unwrap());
            info.hits = tree.root().hit_test(info.position.to_px(tree.scale_factor()));

            let target = if let Some(t) = info.hits.target() {
                tree.get(t.widget_id).map(|w| w.interaction_path()).unwrap_or_else(|| {
                    tracing::error!("hits target `{}` not found", t.widget_id);
                    tree.root().interaction_path()
                })
            } else {
                tree.root().interaction_path()
            }
            .unblocked();

            if let Some(target) = target {
                if info.target != target {
                    let capture = POINTER_CAPTURE.current_capture_value();
                    let prev = mem::replace(&mut info.target, target.clone());

                    let args = TouchedArgs::now(
                        info.target.window_id(),
                        None,
                        *touch,
                        info.touch_propagation.clone(),
                        info.position,
                        info.force,
                        TouchPhase::Move,
                        info.hits.clone(),
                        prev,
                        target,
                        capture.clone(),
                        capture,
                    );
                    TOUCHED_EVENT.notify(args);
                }
            } else {
                window_blocked_remove.push(*touch);
            }
        }

        for touch in window_blocked_remove {
            if let Some(i) = self.pressed.remove(&touch) {
                i.touch_propagation.stop();
                let args = TouchedArgs::now(
                    i.target.window_id(),
                    None,
                    touch,
                    i.touch_propagation,
                    DipPoint::splat(Dip::new(-1)),
                    None,
                    TouchPhase::Cancel,
                    HitTestInfo::no_hits(i.target.window_id()),
                    i.target,
                    None,
                    None,
                    None,
                );
                TOUCHED_EVENT.notify(args);
            }
        }
    }
}

struct PendingDoubleTap {
    window_id: WindowId,
    device_id: DeviceId,
    target: WidgetId,
    count: NonZeroU32,
    timestamp: DInstant,
}
struct PendingTap {
    window_id: WindowId,
    device_id: DeviceId,
    touch: TouchId,
    target: WidgetId,

    propagation: EventPropagationHandle,
}
impl PendingTap {
    /// Check if the tap is still possible after a touch move..
    ///
    /// Returns `true` if it is.
    fn retain(&self, window_id: WindowId, device_id: DeviceId, touch: TouchId) -> bool {
        if self.propagation.is_stopped() {
            // cancel, gesture opportunity handled.
            return false;
        }

        if window_id != self.window_id || device_id != self.device_id {
            // cancel, not same source or target.
            return false;
        }

        if touch != self.touch {
            // cancel, multi-touch.
            return false;
        }

        // retain
        true
    }
}

struct PendingLongPress {
    window_id: WindowId,
    device_id: DeviceId,
    touch: TouchId,
    target: WidgetId,
    position: DipPoint,
    start_time: DInstant,
    modifiers: ModifiersState,

    propagation: EventPropagationHandle,

    delay: DeadlineVar,
    canceled: bool,
}

#[derive(Default)]
struct LongPressGesture {
    pending: Option<PendingLongPress>,
}
impl LongPressGesture {
    fn on_input(&mut self, args: &TouchInputArgs) {
        match args.phase {
            TouchPhase::Start => {
                if let Some(p) = &mut self.pending {
                    // only valid if single touch contact, we use the `pending` presence to track this.
                    p.canceled = true;
                } else if TOUCH_LONG_PRESS_EVENT.has_hooks()
                    || args.target.widgets_path().iter().any(|w| TOUCH_LONG_PRESS_EVENT.is_subscriber(*w))
                {
                    self.pending = Some(PendingLongPress {
                        window_id: args.window_id,
                        device_id: args.device_id,
                        touch: args.touch,
                        position: args.position,
                        start_time: args.timestamp,
                        modifiers: args.modifiers,
                        target: args.target.widget_id(),
                        propagation: args.touch_propagation.clone(),
                        delay: TIMERS.deadline(TOUCH.touch_config().get().tap_max_time),
                        canceled: false,
                    });
                }
            }
            TouchPhase::End | TouchPhase::Cancel => {
                if let Some(p) = &self.pending {
                    if args.touch_propagation == p.propagation {
                        self.pending = None;
                    }
                }
            }
            TouchPhase::Move => unreachable!(),
        }
    }

    fn on_move(&mut self, args: &TouchMoveArgs) {
        if let Some(p) = &mut self.pending {
            if !p.canceled && !p.propagation.is_stopped() {
                for m in &args.touches {
                    if p.propagation == m.touch_propagation {
                        let dist = p.position - m.position().to_vector();
                        let max = TOUCH.touch_config().get().tap_area;
                        if dist.x.abs() > max.width || dist.y.abs() > max.height {
                            p.canceled = true;
                            break;
                        }
                    } else {
                        p.canceled = true;
                        break;
                    }
                }
            }
        }
    }

    fn on_update(&mut self) {
        if let Some(p) = &mut self.pending {
            if !p.canceled && !p.propagation.is_stopped() && p.delay.get().has_elapsed() {
                if let Ok(w) = WINDOWS.widget_tree(p.window_id) {
                    if let Some(w) = w.get(p.target) {
                        let hits = w.hit_test(p.position.to_px(w.tree().scale_factor()));
                        if hits.contains(p.target) {
                            p.propagation.stop();

                            let args = TouchLongPressArgs::now(
                                p.window_id,
                                p.device_id,
                                p.touch,
                                p.position,
                                hits,
                                w.interaction_path(),
                                p.modifiers,
                                p.start_time,
                            );
                            TOUCH_LONG_PRESS_EVENT.notify(args);
                            return;
                        }
                    }
                }
                p.canceled = true;
            }
        }
    }

    fn clear(&mut self) {
        self.pending = None;
    }
}

#[derive(Default)]
struct TapGesture {
    pending_double: Option<PendingDoubleTap>,
    pending: Option<PendingTap>,
}
impl TapGesture {
    fn on_input(&mut self, args: &TouchInputArgs) {
        match args.phase {
            TouchPhase::Start => {
                if self.pending.is_some() {
                    self.pending = None;
                    self.pending_double = None;
                } else if TOUCH_TAP_EVENT.has_hooks() || args.target.widgets_path().iter().any(|w| TOUCH_TAP_EVENT.is_subscriber(*w)) {
                    self.pending = Some(PendingTap {
                        window_id: args.window_id,
                        device_id: args.device_id,
                        touch: args.touch,
                        target: args.target.widget_id(),
                        propagation: args.touch_propagation.clone(),
                    });
                }
            }
            TouchPhase::End => {
                let pending_double = self.pending_double.take();

                if let Some(p) = self.pending.take() {
                    if !p.retain(args.window_id, args.device_id, args.touch) {
                        return;
                    }

                    p.propagation.stop(); // touch_propagation always is stopped after touch end.

                    let tree = if let Ok(w) = WINDOWS.widget_tree(args.window_id) {
                        w
                    } else {
                        return;
                    };

                    match tree.get(p.target) {
                        Some(t) => {
                            if !t.hit_test(args.position.to_px(tree.scale_factor())).contains(p.target) {
                                // cancel, touch did not end over target.
                                return;
                            }
                        }
                        None => return,
                    }

                    if let Some(target) = args.target.sub_path(p.target) {
                        let tap_count = if let Some(double) = pending_double {
                            let cfg = TOUCH.touch_config().get();
                            if double.window_id == p.window_id
                                && double.device_id == p.device_id
                                && double.target == p.target
                                && double.timestamp.elapsed() <= cfg.double_tap_max_time
                            {
                                NonZeroU32::new(double.count.get() + 1).unwrap()
                            } else {
                                NonZeroU32::new(1).unwrap()
                            }
                        } else {
                            NonZeroU32::new(1).unwrap()
                        };

                        self.pending_double = Some(PendingDoubleTap {
                            window_id: args.window_id,
                            device_id: args.device_id,
                            target: p.target,
                            count: tap_count,
                            timestamp: args.timestamp,
                        });

                        TOUCH_TAP_EVENT.notify(TouchTapArgs::new(
                            args.timestamp,
                            args.propagation().clone(),
                            p.window_id,
                            p.device_id,
                            p.touch,
                            args.position,
                            args.hits.clone(),
                            target.into_owned(),
                            args.modifiers,
                            tap_count,
                        ));
                    }
                }
            }
            TouchPhase::Cancel => {
                if let Some(p) = self.pending.take() {
                    p.propagation.stop();
                }
                self.pending = None;
                self.pending_double = None;
            }
            TouchPhase::Move => unreachable!(),
        }
    }

    fn on_move(&mut self, args: &TouchMoveArgs) {
        if let Some(p) = &self.pending {
            for t in &args.touches {
                if !p.retain(args.window_id, args.device_id, t.touch) {
                    self.pending = None;
                    self.pending_double = None;
                    break;
                }
            }
        }
    }

    fn clear(&mut self) {
        self.pending = None;
        self.pending_double = None;
    }
}

/// Info useful for touch gestures computed from two touch points.
#[derive(Clone, Debug, PartialEq, serde::Serialize, serde::Deserialize)]
pub struct TouchTransformInfo {
    /// The two touch contact points.
    pub touches: [euclid::Point2D<f32, Px>; 2],

    /// Middle of the line between the two points.
    pub center: euclid::Point2D<f32, Px>,

    /// Deviation from the points to the center.
    ///
    /// Min 1.0
    pub deviation: f32,

    /// Deviation from the points.x to the center.x.
    ///
    /// Min 1.0
    pub deviation_x: f32,

    /// Deviation from the points.y to the center.y.
    ///
    /// Min 1.0
    pub deviation_y: f32,

    /// Angle of the line.
    pub angle: AngleRadian,
}
impl TouchTransformInfo {
    /// Compute the line info.
    pub fn new_f32(touches: [euclid::Point2D<f32, Px>; 2]) -> Self {
        let a = touches[0].to_vector();
        let b = touches[1].to_vector();

        let center = (a + b) / 2.0;
        let deviation = (a - center).length();
        let deviation_x = (a.x - center.x).abs();
        let deviation_y = (a.y - center.y).abs();

        Self {
            touches,
            center: center.to_point(),
            deviation: deviation.max(1.0),
            deviation_x: deviation_x.max(1.0),
            deviation_y: deviation_y.max(1.0),
            angle: AngleRadian((a.y - b.y).atan2(a.x - b.x)),
        }
    }

    /// Compute the line info, from round pixels.
    pub fn new(touches: [PxPoint; 2]) -> Self {
        Self::new_f32([touches[0].to_f32(), touches[1].to_f32()])
    }

    /// Compute the line info, from device independent pixels.
    pub fn new_dip(touches: [DipPoint; 2], scale_factor: Factor) -> Self {
        Self::new_f32([touches[0].to_f32().to_px(scale_factor), touches[1].to_f32().to_px(scale_factor)])
    }
}
impl TouchTransformInfo {
    /// Computes the translation to transform from `self` to `other`.
    pub fn translation(&self, other: &Self) -> euclid::Vector2D<f32, Px> {
        other.center.to_vector() - self.center.to_vector()
    }

    /// Computes the translation-x to transform from `self` to `other`.
    pub fn translation_x(&self, other: &Self) -> f32 {
        other.center.x - self.center.x
    }

    /// Computes the translation-y to transform from `self` to `other`.
    pub fn translation_y(&self, other: &Self) -> f32 {
        other.center.y - self.center.y
    }

    /// Computes the rotation to transform from `self` to `other`.
    pub fn rotation(&self, other: &Self) -> AngleRadian {
        other.angle - self.angle
    }

    /// Computes the scale to transform from `self` to `other`.
    pub fn scale(&self, other: &Self) -> Factor {
        Factor(other.deviation / self.deviation)
    }

    /// Computes the scale-y to transform from `self` to `other`.
    pub fn scale_x(&self, other: &Self) -> Factor {
        Factor(other.deviation_x / self.deviation_x)
    }

    /// Computes the scale-y to transform from `self` to `other`.
    pub fn scale_y(&self, other: &Self) -> Factor {
        Factor(other.deviation_y / self.deviation_y)
    }

    /// Computes the transform from `self` to `other`.
    pub fn transform(&self, other: &Self, mode: TouchTransformMode) -> PxTransform {
        let mut m = PxTransform::identity();

        if mode.contains(TouchTransformMode::TRANSLATE) {
            m = m.then_translate(self.translation(other));
        } else if mode.contains(TouchTransformMode::TRANSLATE_X) {
            let t = euclid::vec2(self.translation_x(other), 0.0);
            m = m.then_translate(t);
        } else if mode.contains(TouchTransformMode::TRANSLATE_Y) {
            let t = euclid::vec2(0.0, self.translation_y(other));
            m = m.then_translate(t);
        }

        if mode.contains(TouchTransformMode::SCALE) {
            let s = self.scale(other).0;
            m = m.then(&PxTransform::scale(s, s));
        } else if mode.contains(TouchTransformMode::SCALE_X) {
            let s = self.scale_x(other);
            m = m.then(&PxTransform::scale(s.0, 1.0))
        } else if mode.contains(TouchTransformMode::SCALE_Y) {
            let s = self.scale_y(other);
            m = m.then(&PxTransform::scale(1.0, s.0))
        }

        if mode.contains(TouchTransformMode::ROTATE) {
            let a = self.rotation(other);
            m = m.then(&PxTransform::rotation(0.0, 0.0, a.into()));
        }

        m
    }

    /// If the transform is only a translate calculated from a single touch contact.
    pub fn is_single(&self) -> bool {
        self.touches[0] == self.touches[1]
    }
}
impl ops::AddAssign<euclid::Vector2D<f32, Px>> for TouchTransformInfo {
    fn add_assign(&mut self, rhs: euclid::Vector2D<f32, Px>) {
        self.touches[0] += rhs;
        self.touches[1] += rhs;
        self.center += rhs;
    }
}
impl ops::Add<euclid::Vector2D<f32, Px>> for TouchTransformInfo {
    type Output = Self;

    fn add(mut self, rhs: euclid::Vector2D<f32, Px>) -> Self::Output {
        self += rhs;
        self
    }
}
impl ops::AddAssign<PxVector> for TouchTransformInfo {
    fn add_assign(&mut self, rhs: PxVector) {
        *self += rhs.cast::<f32>();
    }
}
impl ops::Add<PxVector> for TouchTransformInfo {
    type Output = Self;

    fn add(mut self, rhs: PxVector) -> Self::Output {
        self += rhs;
        self
    }
}
impl ops::SubAssign<euclid::Vector2D<f32, Px>> for TouchTransformInfo {
    fn sub_assign(&mut self, rhs: euclid::Vector2D<f32, Px>) {
        self.touches[0] -= rhs;
        self.touches[1] -= rhs;
        self.center -= rhs;
    }
}
impl ops::Sub<euclid::Vector2D<f32, Px>> for TouchTransformInfo {
    type Output = Self;

    fn sub(mut self, rhs: euclid::Vector2D<f32, Px>) -> Self::Output {
        self -= rhs;
        self
    }
}
impl ops::SubAssign<PxVector> for TouchTransformInfo {
    fn sub_assign(&mut self, rhs: PxVector) {
        *self -= rhs.cast::<f32>();
    }
}
impl ops::Sub<PxVector> for TouchTransformInfo {
    type Output = Self;

    fn sub(mut self, rhs: PxVector) -> Self::Output {
        self -= rhs;
        self
    }
}

bitflags! {
    /// Defines the different transforms that a touch transform can do to keep
    /// two touch points in a widget aligned with the touch contacts.
    #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
    #[serde(transparent)]
    pub struct TouchTransformMode: u8 {
        /// Can translate in the X dimension.
        const TRANSLATE_X = 0b0000_0001;
        /// Can translate in the y dimension.
        const TRANSLATE_Y = 0b0000_0010;
        /// Can translate in both dimensions.
        const TRANSLATE = Self::TRANSLATE_X.bits() | Self::TRANSLATE_Y.bits();

        /// Can scale in the X dimension.
        const SCALE_X = 0b0000_0100;
        /// Can scale in the Y dimension.
        const SCALE_Y = 0b0000_1000;
        /// Can scale in both dimensions the same amount.
        const SCALE = 0b0001_1100;

        /// Can rotate.
        const ROTATE = 0b0010_0000;

        /// Can translate, scale-square and rotate.
        const ALL = Self::TRANSLATE.bits()| Self::SCALE.bits() | Self::ROTATE.bits();
    }
}
impl_from_and_into_var! {
    fn from(all_or_empty: bool) -> TouchTransformMode {
        if all_or_empty {
            TouchTransformMode::ALL
        } else {
            TouchTransformMode::empty()
        }
    }
}

#[derive(Default)]
enum TransformGesture {
    #[default]
    NoStartedZero,

    NotStartedOne {
        window_id: WindowId,
        device_id: DeviceId,
        start_position: DipPoint,
        position: DipPoint,
        handle: EventPropagationHandle,
    },
    NotStartedTwo {
        window_id: WindowId,
        device_id: DeviceId,
        start_position: [DipPoint; 2],
        position: [DipPoint; 2],
        handle: [EventPropagationHandle; 2],
        scale_factor: Factor,
    },

    StartedOne {
        window_id: WindowId,
        device_id: DeviceId,
        position: DipPoint,
        velocity: DipVector,
        scale_factor: Factor,
        handle: EventPropagationHandle,
        first_info: TouchTransformInfo,
        hits: HitTestInfo,
        target: InteractionPath,
    },
    StartedTwo {
        window_id: WindowId,
        device_id: DeviceId,
        position: [DipPoint; 2],
        velocity: [DipVector; 2],
        scale_factor: Factor,
        handle: [EventPropagationHandle; 2],
        first_info: TouchTransformInfo,
        hits: HitTestInfo,
        target: InteractionPath,
    },
}
impl TransformGesture {
    fn on_input(&mut self, args: &TouchInputArgs) {
        match mem::take(self) {
            Self::NoStartedZero => {
                if TouchPhase::Start == args.phase
                    && !args.touch_propagation.is_stopped()
                    && (TOUCH_TRANSFORM_EVENT.has_hooks()
                        || args.target.widgets_path().iter().any(|w| TOUCH_TRANSFORM_EVENT.is_subscriber(*w)))
                {
                    *self = Self::NotStartedOne {
                        window_id: args.window_id,
                        device_id: args.device_id,
                        start_position: args.position,
                        position: args.position,
                        handle: args.touch_propagation.clone(),
                    }
                }
            }
            Self::NotStartedOne {
                window_id,
                device_id,
                position,
                handle,
                ..
            } => {
                if TouchPhase::Start == args.phase
                    && window_id == args.window_id
                    && device_id == args.device_id
                    && !args.touch_propagation.is_stopped()
                    && !handle.is_stopped()
                    && handle != args.touch_propagation
                {
                    if let Ok(w) = WINDOWS.widget_tree(args.window_id) {
                        *self = Self::NotStartedTwo {
                            window_id: args.window_id,
                            device_id: args.device_id,
                            start_position: [position, args.position],
                            position: [position, args.position],
                            handle: [handle, args.touch_propagation.clone()],
                            scale_factor: w.scale_factor(),
                        }
                    }
                }
            }
            Self::NotStartedTwo { .. } => {
                // cancel before start
            }
            Self::StartedOne {
                window_id,
                device_id,
                position,
                velocity,
                scale_factor,
                handle,
                first_info,
                hits,
                target,
            } => match args.phase {
                TouchPhase::Start
                    if window_id == args.window_id
                        && device_id == args.device_id
                        && !args.touch_propagation.is_stopped()
                        && !handle.is_stopped()
                        && handle != args.touch_propagation =>
                {
                    *self = Self::StartedTwo {
                        window_id,
                        device_id,
                        position: [position, args.position],
                        velocity: [velocity, args.velocity],
                        scale_factor,
                        handle: [handle, args.touch_propagation.clone()],
                        first_info,
                        hits,
                        target,
                    };
                }
                TouchPhase::Move => unreachable!(),
                TouchPhase::End if handle == args.touch_propagation => {
                    let position = args.position;

                    let latest_info = TouchTransformInfo::new_dip([position, position], scale_factor);
                    let capture = POINTER_CAPTURE.current_capture_value();

                    let velocity = velocity.to_px(scale_factor);

                    let args = TouchTransformArgs::now(
                        window_id,
                        device_id,
                        first_info,
                        latest_info,
                        [velocity, velocity],
                        scale_factor,
                        TouchPhase::End,
                        hits,
                        target,
                        capture,
                        args.modifiers,
                    );
                    TOUCH_TRANSFORM_EVENT.notify(args);
                }
                _ => {
                    // cancel or invalid start
                    *self = Self::StartedOne {
                        window_id,
                        device_id,
                        position,
                        velocity,
                        scale_factor,
                        handle,
                        first_info,
                        hits,
                        target,
                    };
                    self.clear();
                }
            },
            Self::StartedTwo {
                window_id,
                device_id,
                mut position,
                velocity,
                scale_factor,
                handle,
                first_info,
                hits,
                target,
            } => {
                if TouchPhase::End == args.phase && handle.iter().any(|h| h == &args.touch_propagation) {
                    let i = handle.iter().position(|h| h == &args.touch_propagation).unwrap();
                    position[i] = args.position;

                    let latest_info = TouchTransformInfo::new_dip(position, scale_factor);
                    let capture = POINTER_CAPTURE.current_capture_value();

                    let velocity = [velocity[0].to_px(scale_factor), velocity[1].to_px(scale_factor)];

                    let args = TouchTransformArgs::now(
                        window_id,
                        device_id,
                        first_info,
                        latest_info,
                        velocity,
                        scale_factor,
                        TouchPhase::End,
                        hits,
                        target,
                        capture,
                        args.modifiers,
                    );
                    TOUCH_TRANSFORM_EVENT.notify(args);
                } else {
                    *self = Self::StartedTwo {
                        window_id,
                        device_id,
                        position,
                        velocity,
                        scale_factor,
                        handle,
                        first_info,
                        hits,
                        target,
                    };
                    self.clear();
                }
            }
        }
    }

    fn on_move(&mut self, args: &TouchMoveArgs) {
        match self {
            Self::NoStartedZero => {}
            Self::NotStartedOne {
                start_position,
                position,
                handle,
                window_id,
                device_id,
            } => {
                if handle.is_stopped() {
                    *self = Self::NoStartedZero;
                } else {
                    let mut moved = false;
                    for t in &args.touches {
                        if handle == &t.touch_propagation {
                            *position = t.position();
                            moved = true;
                        } else {
                            *self = Self::NoStartedZero;
                            return;
                        }
                    }
                    if moved {
                        let cfg = TOUCH.touch_config().get();
                        if (position.x - start_position.x).abs() > cfg.double_tap_area.width
                            || (position.y - start_position.y).abs() > cfg.double_tap_area.height
                        {
                            if let Ok(w) = WINDOWS.widget_tree(*window_id) {
                                let scale_factor = w.scale_factor();
                                let first_info = TouchTransformInfo::new_dip([*start_position, *start_position], scale_factor);
                                let latest_info = TouchTransformInfo::new_dip([*position, *position], scale_factor);

                                let hits = w.root().hit_test(first_info.center.cast());
                                let target = hits
                                    .target()
                                    .and_then(|t| w.get(t.widget_id))
                                    .map(|t| t.interaction_path())
                                    .unwrap_or_else(|| w.root().interaction_path());

                                let target = match target.unblocked() {
                                    Some(t) => t,
                                    None => {
                                        *self = Self::NoStartedZero;
                                        return; // entire window blocked
                                    }
                                };
                                let capture = POINTER_CAPTURE.current_capture_value();

                                // takeover the gesture.
                                handle.stop();

                                let args = TouchTransformArgs::now(
                                    *window_id,
                                    *device_id,
                                    first_info.clone(),
                                    latest_info,
                                    [PxVector::zero(); 2],
                                    scale_factor,
                                    TouchPhase::Start,
                                    hits.clone(),
                                    target.clone(),
                                    capture,
                                    args.modifiers,
                                );
                                TOUCH_TRANSFORM_EVENT.notify(args);

                                *self = Self::StartedOne {
                                    window_id: *window_id,
                                    device_id: *device_id,
                                    position: *position,
                                    velocity: DipVector::zero(),
                                    scale_factor,
                                    handle: handle.clone(),
                                    first_info,
                                    hits,
                                    target,
                                };
                            } else {
                                *self = Self::NoStartedZero;
                            }
                        }
                    }
                }
            }
            Self::NotStartedTwo {
                start_position,
                position,
                handle,
                scale_factor,
                window_id,
                device_id,
            } => {
                if handle[0].is_stopped() || handle[1].is_stopped() {
                    *self = Self::NoStartedZero;
                } else {
                    let mut any_moved = false;
                    for t in &args.touches {
                        if let Some(i) = handle.iter().position(|h| h == &t.touch_propagation) {
                            position[i] = t.position();
                            any_moved = true;
                        } else {
                            *self = Self::NoStartedZero;
                            return;
                        }
                    }

                    if any_moved {
                        let first_info = TouchTransformInfo::new_dip(*start_position, *scale_factor);
                        let latest_info = TouchTransformInfo::new_dip(*position, *scale_factor);

                        let start = {
                            let translation = first_info.translation(&latest_info);
                            translation.x > 0.0 && translation.y > 0.0
                        } || {
                            let scale = first_info.scale(&latest_info);
                            scale.0 != 1.0
                        } || {
                            let rotate = first_info.rotation(&latest_info);
                            rotate.0 != 0.0
                        };

                        if start {
                            if let Ok(w) = WINDOWS.widget_tree(*window_id) {
                                let hits = w.root().hit_test(first_info.center.cast());
                                let target = hits
                                    .target()
                                    .and_then(|t| w.get(t.widget_id))
                                    .map(|t| t.interaction_path())
                                    .unwrap_or_else(|| w.root().interaction_path());

                                let target = match target.unblocked() {
                                    Some(t) => t,
                                    None => {
                                        *self = Self::NoStartedZero;
                                        return; // entire window blocked
                                    }
                                };
                                let capture = POINTER_CAPTURE.current_capture_value();

                                for h in handle.iter() {
                                    // takeover the gesture.
                                    h.stop();
                                }

                                let args = TouchTransformArgs::now(
                                    *window_id,
                                    *device_id,
                                    first_info.clone(),
                                    latest_info,
                                    [PxVector::zero(); 2],
                                    *scale_factor,
                                    TouchPhase::Start,
                                    hits.clone(),
                                    target.clone(),
                                    capture,
                                    args.modifiers,
                                );
                                TOUCH_TRANSFORM_EVENT.notify(args);

                                *self = Self::StartedTwo {
                                    window_id: *window_id,
                                    device_id: *device_id,
                                    position: *position,
                                    velocity: [DipVector::zero(); 2],
                                    scale_factor: *scale_factor,
                                    handle: handle.clone(),
                                    first_info,
                                    hits,
                                    target,
                                };
                            } else {
                                *self = Self::NoStartedZero;
                            }
                        }
                    }
                }
            }
            Self::StartedOne {
                window_id,
                device_id,
                position,
                velocity,
                scale_factor,
                handle,
                first_info,
                hits,
                target,
            } => {
                let mut any_moved = false;
                for t in &args.touches {
                    if handle == &t.touch_propagation {
                        *position = t.position();
                        *velocity = t.velocity;
                        any_moved = true;
                    } else {
                        self.clear();
                        return;
                    }
                }

                if any_moved {
                    let latest_info = TouchTransformInfo::new_dip([*position, *position], *scale_factor);
                    let capture = POINTER_CAPTURE.current_capture_value();

                    let velocity = velocity.to_px(*scale_factor);

                    let args = TouchTransformArgs::now(
                        *window_id,
                        *device_id,
                        first_info.clone(),
                        latest_info,
                        [velocity, velocity],
                        *scale_factor,
                        TouchPhase::Move,
                        hits.clone(),
                        target.clone(),
                        capture,
                        args.modifiers,
                    );
                    TOUCH_TRANSFORM_EVENT.notify(args);
                }
            }
            Self::StartedTwo {
                window_id,
                device_id,
                position,
                scale_factor,
                velocity,
                handle,
                first_info,
                hits,
                target,
            } => {
                let mut any_moved = false;
                for t in &args.touches {
                    if let Some(i) = handle.iter().position(|h| h == &t.touch_propagation) {
                        position[i] = t.position();
                        velocity[i] = t.velocity;
                        any_moved = true;
                    } else {
                        self.clear();
                        return;
                    }
                }

                if any_moved {
                    let latest_info = TouchTransformInfo::new_dip(*position, *scale_factor);
                    let capture = POINTER_CAPTURE.current_capture_value();

                    let velocity = [velocity[0].to_px(*scale_factor), velocity[1].to_px(*scale_factor)];

                    let args = TouchTransformArgs::now(
                        *window_id,
                        *device_id,
                        first_info.clone(),
                        latest_info,
                        velocity,
                        *scale_factor,
                        TouchPhase::Move,
                        hits.clone(),
                        target.clone(),
                        capture,
                        args.modifiers,
                    );
                    TOUCH_TRANSFORM_EVENT.notify(args);
                }
            }
        }
    }

    fn clear(&mut self) {
        match mem::take(self) {
            TransformGesture::StartedOne {
                window_id,
                device_id,
                scale_factor,
                first_info,
                hits,
                target,
                ..
            }
            | TransformGesture::StartedTwo {
                window_id,
                device_id,
                scale_factor,
                first_info,
                hits,
                target,
                ..
            } => {
                let args = TouchTransformArgs::now(
                    window_id,
                    device_id,
                    first_info.clone(),
                    first_info,
                    [PxVector::zero(); 2],
                    scale_factor,
                    TouchPhase::Cancel,
                    hits,
                    target,
                    None,
                    ModifiersState::empty(),
                );
                TOUCH_TRANSFORM_EVENT.notify(args);
            }
            _ => {}
        }
    }
}