ngen 0.1.4

A very simple game engine using OpenGL
Documentation 
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use sdl2::Sdl;

#[derive(Clone, Copy, Debug)]
pub struct Tick {
    pub total_time: f64,
    pub dt: f32,
    pub frame: u64,
}

pub struct Timer {
    dt: f64,
    freq: f64,
    max_frame: f64,
    total_time: f64,
    accumulator: f64,
    current_time: f64,
    frame: u64,
    subsystem: sdl2::TimerSubsystem,
}

impl Timer {
    pub fn new(context: &Sdl, dt: f64, max_frame: f64) -> Result<Self, String> {
        let subsystem = context.timer()?;
        let freq = subsystem.performance_frequency() as f64;
        let current_time = subsystem.performance_counter() as f64 / freq;

        Ok(Self {
            dt,
            freq,
            max_frame,
            total_time: 0.,
            accumulator: 0.,
            current_time,
            frame: 0,
            subsystem,
        })
    }

    fn get_time(&self) -> f64 {
        (self.subsystem.performance_counter() as f64) / self.freq
    }

    pub fn begin_frame<'a>(&'a mut self) -> TimeIter<'a> {
        let new_time = self.get_time();
        let frame_time = (new_time - self.current_time).min(self.max_frame);

        self.current_time = new_time;
        self.accumulator += frame_time;

        TimeIter { timer: self }
    }

    pub const fn get_tick(&self) -> Tick {
        Tick {
            total_time: self.total_time,
            dt: self.dt as f32,
            frame: self.frame,
        }
    }

    fn has_accumulator_remaining(&self) -> bool {
        self.accumulator >= self.dt
    }

    fn reduce_accumulator(&mut self) {
        self.accumulator -= self.dt;
        self.total_time += self.dt;
    }

    #[allow(dead_code)]
    pub const fn dt(&self) -> f32 {
        self.dt as f32
    }

    #[allow(dead_code)]
    pub const fn total_time(&self) -> f32 {
        self.total_time as f32
    }
}

pub struct TimeIter<'a> {
    timer: &'a mut Timer,
}

impl<'a> Iterator for TimeIter<'a> {
    type Item = Tick;

    fn next(&mut self) -> Option<Self::Item> {
        let timer = &mut self.timer;
        if timer.has_accumulator_remaining() {
            timer.frame += 1;

            let tick = timer.get_tick();
            timer.reduce_accumulator();

            return Some(tick);
        }

        None
    }
}