Struct iyes_loopless::fixedtimestep::FixedTimestepStage

pub struct FixedTimestepStage { /* private fields */ }

A Stage that runs a number of child stages with a fixed timestep

You can set the timestep duration. Every frame update, the time delta will be accumulated, and the child stages will run when it goes over the timestep threshold. If multiple timesteps have been accumulated, the child stages will be run multiple times.

You can add multiple child stages, allowing you to use Commands in your fixed timestep systems, and have their effects applied.

A good place to add the FixedTimestepStage is usually before CoreStage::Update.

Implementations

impl FixedTimestepStage

pub fn from_stage<S: Stage>(timestep: Duration, stage: S) -> Self

Helper to create a FixedTimestepStage with a single child stage

pub fn new(timestep: Duration) -> Self

Create a new empty FixedTimestepStage with no child stages

pub fn add_stage<S: Stage>(&mut self, stage: S)

Add a child stage

pub fn with_stage<S: Stage>(self, stage: S) -> Self

Builder method for adding a child stage

pub fn set_rate_lock(&mut self, n_frames: u32, exit_deviation: f32)

Enable EXPERIMENTAL “rate locking” algorithm

The idea is to detect if the fixed timestep rate is “close enough” to the actual update rate, and if yes, stop accumulating delta time, to run cleanly without hickups/jitter (at the real update rate, instead of the set timestep duration).

For example, if you set a timestep of 1.0/60.0 seconds, and run with vsync on a typical 59.97Hz monitor, you might prefer to just get one fixed update per frame anyway, instead of occasional hickups/jitter due to the subtle mismatch between the fixed timestep and the real rate.

The algorithm works as follows: count how many timesteps get executed each frame, and if the number doesn’t change for n_frames consecutive frames, enter “locked mode”. While in locked mode, reset the accumulator to half the step duration at the start of each execution. If, at any time, there is a frame that causes the accumulator to deviate by more than exit_deviation timestep durations, leave “locked mode”.

Reasonable parameters: n_frames: 5 to 15, exit_deviation: 0.05 to 0.1.

pub fn with_rate_lock(self, n_frames: u32, exit_deviation: f32) -> Self

Builder-style method for [set_rate_lock]

Trait Implementations

impl Stage for FixedTimestepStage

fn run(&mut self, world: &mut World)

Runs the stage; this happens once per update. Implementors must initialize all of their state and systems before running the first time.