# chron

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A game loop with a fixed timestep.

Features:

- A fixed timestep.
  Updates to the game logic (`chron::Tick::Update`) are independent from the rendering of new frames (`chron::Tick::Render`).
  Updates are emitted at fixed intervals.
  Renders are emitted in between updates: the frame rate may either be unlocked (the default) or limited (see below).
- An optional *maximum frame rate*, to prevent the game from running at unnecessarily high frame rates.
  When the *maximum frame rate* is not set, the frame rate is unlocked, i.e. the loop will emit as many `chron::Tick::Render` events as possible in between two updates.
  To set the *maximum frame rate* use the function `Clock::max_frame_rate`.
- An optional way to prevent an infinite update loop.
  When the loop cannot maintain the specified *updates per second* (e.g. because updates are taking too long) it has to play catch-up by only emitting updates and **no** renders.
  This setting limits how many updates are emitted before a render is enforced.
  It prevents the game from never rendering at all, at the cost of slowing down even more.
  To set the *maximum updates per frame* use the function `Clock::max_updates_per_frame`.

> Note: The *maximum frame rate* feature uses [`std::thread::sleep`](https://doc.rust-lang.org/std/thread/fn.sleep.html#platform-specific-behavior).
> Its accuracy may or may not be good enough, depending on the platform.
> So far it seems to work fine (on Linux).

## Example

```rust
use std::num::NonZeroU32;

let updates_per_second = NonZeroU32::new(50).unwrap();
let frames_per_second = NonZeroU32::new(60).unwrap();

let clock = chron::Clock::new(updates_per_second)
    .max_frame_rate(frames_per_second)
    .max_updates_per_frame(10);

for tick in clock {
    match tick {
        chron::Tick::Update => {
            // ...
        }
        chron::Tick::Render { interpolation } => {
            // ...
        }
    }
}
```