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// This file is part of Carambolage.

// Carambolage is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Carambolage is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Foobar.  If not, see <http://www.gnu.org/licenses/>.
use time::{Duration, PreciseTime};

/// Limits the FPS to chosen value.
///
/// This is just a utility, that's why you have to limit the frame rate
/// externally.
/// # Example
/// ```
/// # fn main() {
/// let frame_limiter = FrameLimiter::new(60);
/// // GameLoop {
///     // Warning: delta_time will be one millisecond on first start().
///     let delta_time = frame_limiter.start();
///     // Game stuff
///     frame_limiter.stop();
///     assert!(false);
/// // }
/// # }
/// ```
pub struct FrameLimiter {
    time_per_frame: Duration,
    delta_time: Duration,
    dt: f32,
    time: PreciseTime,
}

impl FrameLimiter {
    /// Create a new FrameLimiter.
    ///
    /// Set the `frame_rate` as u32.
    pub fn new(frame_rate: u32) -> FrameLimiter {
        let time_per_frame = if frame_rate == 0 {
            Duration::nanoseconds(1)
        } else {
            Duration::nanoseconds((1e9 / f64::from(frame_rate)) as i64)
        };
        let time = PreciseTime::now();

        FrameLimiter {
            time_per_frame,
            delta_time: Duration::microseconds(1),
            dt: 1e-6f32,
            time,
        }
    }

    /// Make this the very first function call of your game loop, so all calculations add to delta time.
    /// This function returns the delta time.
    pub fn start(&mut self) -> f32 {
        let now = PreciseTime::now();
        self.time = now;

        self.dt
    }

    /// Make this the very last function call of your game loop.
    pub fn stop(&mut self) -> bool {
        self.delta_time = self.time.to(PreciseTime::now());
        self.dt = (self.delta_time.num_nanoseconds().unwrap() as f64 * 1e-9) as f32;
        self.delta_time < self.time_per_frame
    }
}