1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112

#[cfg(not(target_arch = "wasm32"))] mod default_target;
#[cfg(not(target_arch = "wasm32"))] pub use default_target::game_loop;

#[cfg(target_arch = "wasm32")] mod wasm_target;
#[cfg(target_arch = "wasm32")] pub use wasm_target::game_loop;

pub struct GameLoop<G, T: TimeTrait> {
    pub game: G,
    pub updates_per_second: u32,
    pub max_frame_time: f64,
    pub exit_next_iteration: bool,

    fixed_time_step: f64,
    number_of_updates: u32,
    number_of_renders: u32,
    running_time: f64,
    accumulated_time: f64,
    blending_factor: f64,
    previous_instant: T,
    current_instant: T,
}

impl<G, T: TimeTrait> GameLoop<G, T> {
    pub fn new(game: G, updates_per_second: u32, max_frame_time: f64) -> Self {
        Self {
            game,
            updates_per_second,
            max_frame_time,
            exit_next_iteration: false,

            fixed_time_step: 1.0 / updates_per_second as f64,
            number_of_updates: 0,
            number_of_renders: 0,
            running_time: 0.0,
            accumulated_time: 0.0,
            blending_factor: 0.0,
            previous_instant: T::now(),
            current_instant: T::now(),
        }
    }

    pub fn next_frame<U, R>(&mut self, mut update: U, mut render: R) -> bool
        where U: FnMut(&mut GameLoop<G, T>),
              R: FnMut(&mut GameLoop<G, T>),
    {
        let mut g = self;

        if g.exit_next_iteration {
            return false;
        }

        g.current_instant = T::now();

        let mut elapsed = g.current_instant.sub(&g.previous_instant);

        if elapsed > g.max_frame_time {
            elapsed = g.max_frame_time;
        }

        g.running_time += elapsed;
        g.accumulated_time += elapsed;

        while g.accumulated_time >= g.fixed_time_step {
            update(&mut g);

            g.accumulated_time -= g.fixed_time_step;
            g.number_of_updates += 1;
        }

        g.blending_factor = g.accumulated_time / g.fixed_time_step;

        render(&mut g);

        g.number_of_renders += 1;
        g.previous_instant = g.current_instant;

        return true;
    }

    pub fn exit(&mut self) {
        self.exit_next_iteration = true;
    }

    pub fn fixed_time_step(&self) -> f64 {
        self.fixed_time_step
    }

    pub fn number_of_updates(&self) -> u32 {
        self.number_of_updates
    }

    pub fn number_of_renders(&self) -> u32 {
        self.number_of_renders
    }

    pub fn running_time(&self) -> f64 {
        self.running_time
    }

    pub fn accumulated_time(&self) -> f64 {
        self.accumulated_time
    }

    pub fn blending_factor(&self) -> f64 {
        self.blending_factor
    }
}

pub trait TimeTrait : Copy {
    fn now() -> Self;
    fn sub(&self, other: &Self) -> f64;
}