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//! Position-only layout following, independent of the native measurement adapter.
use crate::{MotionValue, Transition};
use std::time::Duration;
/// A measured position and the offset needed to display its animated presentation.
/// Units are logical pixels in a consistent caller-chosen coordinate space.
#[derive(Clone, Copy, Debug)]
pub struct LayoutPositionFrame {
origin: [f64; 2],
position: [f64; 2],
velocity: [f64; 2],
active: bool,
completed: bool,
}
impl LayoutPositionFrame {
/// The current layout destination, without the animation offset.
pub fn layout_origin(self) -> [f64; 2] {
self.origin
}
/// Presented position in the same coordinate space as the measured origin.
pub fn position(self) -> [f64; 2] {
self.position
}
/// Translation to apply after layout; size is unaffected.
pub fn offset(self) -> [f64; 2] {
std::array::from_fn(|i| crate::value::finite(self.position[i] - self.origin[i]))
}
/// Current velocity in logical pixels per second.
pub fn velocity(self) -> [f64; 2] {
self.velocity
}
/// Whether another sample is required.
pub fn is_animating(self) -> bool {
self.active
}
/// Completion edge when the last active axis finishes.
pub fn just_completed(self) -> bool {
self.completed
}
}
/// Retained position-only layout sampler. First measurement snaps, later measurements
/// interrupt from the current presentation and preserve spring velocity. Sampling allocates
/// no memory. The optional native `LayoutGroup` supplies measurements automatically.
#[derive(Clone, Debug)]
pub struct LayoutPositionState {
axes: [MotionValue; 2],
initialized: bool,
}
impl Default for LayoutPositionState {
fn default() -> Self {
Self {
axes: [MotionValue::new(0.), MotionValue::new(0.)],
initialized: false,
}
}
}
impl LayoutPositionState {
/// Follows a finite layout origin in logical pixels. Panics for non-finite input.
/// Use one monotonic epoch; backward timestamps hold. Reduced motion snaps and
/// completes once. Offsets/velocity are never used as the next layout measurement.
///
/// ```
/// use gpui_ce_motion::{LayoutPositionState, Transition};
/// use std::time::Duration;
/// let mut state = LayoutPositionState::default();
/// state.sample([0., 0.], Transition::default(), Duration::ZERO, false);
/// let moved = state.sample([100., 40.], Transition::default(), Duration::ZERO, false);
/// assert_eq!(moved.position(), [0., 0.]);
/// assert_eq!(moved.offset(), [-100., -40.]);
/// let done = state.sample([100., 40.], Transition::default(), Duration::from_secs(5), false);
/// assert_eq!(done.offset(), [0., 0.]);
/// ```
pub fn sample(
&mut self,
origin: [f64; 2],
transition: Transition,
now: Duration,
reduced_motion: bool,
) -> LayoutPositionFrame {
self.sample_axes(origin, [transition; 2], now, reduced_motion)
}
/// Samples independently timed axes. Instant axes never schedule interpolation;
/// useful for constrained sizing and one-dimensional layout followers.
pub fn sample_axes(
&mut self,
origin: [f64; 2],
transitions: [Transition; 2],
now: Duration,
reduced_motion: bool,
) -> LayoutPositionFrame {
assert!(
origin.iter().all(|v| v.is_finite()),
"layout origin must be finite"
);
if !self.initialized {
for (axis, value) in self.axes.iter_mut().zip(origin) {
axis.jump(value, now);
}
self.initialized = true;
}
let mut active = false;
let mut completed = false;
let mut velocity = [0.; 2];
let position = std::array::from_fn(|i| {
self.axes[i].animate(origin[i], transitions[i], now);
let frame = self.axes[i].sample(now, reduced_motion);
active |= frame.is_animating();
completed |= frame.just_completed();
velocity[i] = frame.velocity();
frame.value()
});
LayoutPositionFrame {
origin,
position,
velocity,
active,
completed: completed && !active,
}
}
/// Forgets measurement history. The next measurement mounts immediately.
pub fn reset(&mut self) {
*self = Self::default();
}
}