sao-ui-rs/src/anim.rs

use keyframe::EasingFunction;

pub struct Animation<F> {
    time: f32,
    duration: f32,
    from: f32,
    to: f32,
    function: F,
    direction: bool,
}

impl<F: EasingFunction> Animation<F> {
    pub fn new(function: F, duration: f32, from: f32, to: f32) -> Self {
        Self {
            time: duration,
            duration,
            from,
            to,
            function,
            direction: false,
        }
    }

    pub fn update(&mut self, dt: f32) {
        self.time += dt;
    }

    pub fn is_active(&self) -> bool {
        self.time < self.duration
    }

    pub fn get(&self) -> f32 {
        if self.is_active() {
            let x = self.time / self.duration;
            let x = if self.direction { x } else { 1.0 - x };
            let lerp = self.function.y(x as f64) as f32;
            (1.0 - lerp) * self.from + lerp * self.to
        } else if self.direction {
            self.to
        } else {
            self.from
        }
    }

    pub fn ease_to(&mut self, duration: f32, to: f32) {
        self.from = self.get();
        self.to = to;
        self.time = 0.0;
        self.duration = duration;
        self.direction = true;
    }

    pub fn ease_in(&mut self) {
        if !self.direction {
            self.ease_toggle();
        }
    }

    pub fn ease_out(&mut self) {
        if self.direction {
            self.ease_toggle();
        }
    }

    pub fn ease_toggle(&mut self) {
        if self.is_active() {
            self.time = self.duration - self.time;
        } else {
            self.time = 0.0;
        }

        self.direction = !self.direction;
    }
}