Module timer 

Timers a game’s rules set and forget, counted in steps or turns: Countdown, which fires once and is the cooldown too, and Every, which repeats. With them, the step rate (STEPS_PER_SECOND) and the two conversions a length in milliseconds goes through (steps_from_ms, ms_from_steps).

A timer says when; a tween (ease) says how far, drawn from the time alone.

Two kinds of time

Simulation time is steps or turns. A tick game steps its rules once for each of input.ticks() and advances its timers by 1 in each step, so a timer fires on the same step at 30 and at 60 frames a second. A turn game advances by 1 where its turn or round ends, in its own TurnRules::apply. Timers live in the state the rules own, so they save, hash (state_hash) and replay with it. A timer moves only when it is advanced, so a paused game’s timers wait.

Presentation time is FrameInput::dt(), Ctx::clock_s and HurryClock, in shuyi-ui: glides, blinks, text typing out, a clock on screen. It may stay in floats, and no rule ever reads it.

use shuyi_core::timer::Every;

// Something that moves every 8 steps. `ticks` stands in for
// `input.ticks()`, the steps due this frame.
let mut mover = Every::new(8);
let mut x = 0;
for ticks in [1, 1, 2, 4, 1, 0, 2] {
    for _ in 0..ticks {
        // One step of the rules.
        x += mover.advance(1);
    }
}
assert_eq!(x, 1);
assert_eq!(mover.until_next(), 5);

Many timers, and things that happen later

Many timers are a BTreeMap<K, Countdown> in the state, never a HashMap, whose order changes the hash (hash). An event that happens later is a Countdown kept beside it, which sends it when it fires.

Values read from a file

Nothing checks a timer read from a hand-edited save. A value out of range (left above length, since at or above period) still behaves by the formulas on each method, and no method panics on it.

Structs

Countdown

A timer that fires once, after length steps or turns, and waits to be restarted.

Every

A timer that fires every period steps or turns.

Constants

STEPS_PER_SECOND

Fixed simulation steps a second.

Functions

ms_from_steps

The milliseconds steps steps last at STEPS_PER_SECOND, rounded down: 0, 16, 33, 50, … and exactly 1000 at step 60, so it never drifts as a whole number of milliseconds per step would. steps_from_ms of it gives steps back while that fits a u32.

steps_from_ms

Whole steps in ms milliseconds at STEPS_PER_SECOND, rounded up, so any time above 0 is at least one step. It turns a length a designer wrote in milliseconds into steps, once, at load. A timer never counts milliseconds.