Fast-forwarding the simulation

[Bauxitedev]

Quick question, is it possible to fast-forward the physics simulation? E.g. if I want to run 10 physics steps per frame instead of 1, which makes the simulation run 10x as fast?

[allsey87]

Just a thought, but perhaps the best solution would be to disable rendering pipeline for those 10 steps?

[sebcrozet]

Perhaps we should add a variant TimeStepMode::MultipleFixedTimesteps(u32) (or simply add the number of timesteps to the TimeStepMode::FixedTimesteps)?

[allsey87]

Perhaps we should add a variant TimeStepMode::MultipleFixedTimesteps(u32)?

One could certainly do this although it seems to me that only updating the physics (and none of the other systems involved in a complete Bevy application) would be a bit of a corner case.

[Bauxitedev]

Just a thought, but perhaps the best solution would be to disable rendering pipeline for those 10 steps?

Not sure if that would work... many other pipelines would have to be disabled as well, right? E.g. the input handling pipeline, the audio pipeline, etc...

[allsey87]

Just a thought, but perhaps the best solution would be to disable rendering pipeline for those 10 steps?

Not sure if that would work... many other pipelines would have to be disabled as well, right? E.g. the input handling pipeline, the audio pipeline, etc...

I don't think there is a correct answer here, although I would be surprised if you really ended up turning off all other systems/pipelines except for physics in the final application.

[sebcrozet]

@Bauxitedev Can you perhaps tell more about your use-case here? That would help understand exactly what you need.

[Bauxitedev]

@sebcrozet I'm writing a small pseudo-scientific simulation that uses genetic algorithms to try to generate efficient vehicles. To find the effectiveness (aka fitness) of a vehicle, I run a physics simulation. E.g. if the vehicle instantly falls over, it gets low fitness. If it manages to traverse rough terrain without falling, it gets high fitness. If I could speed up the physics simulation, I could determine the fitness of a vehicle much faster than currently possible.

[rlidwka]

If you want Fixed timestep mode with dt=A, substeps=B, and execute 10 of these per frame, can you set this?:

TimestepMode::Fixed {
    dt: A * 10.,
    substeps: B * 10,
}

I think it'd have the same effect, unless I misunderstood the initial question.

[Vrixyz]

Am I completely wrong here or as a user, we could change the time scale ? Not sure exactly how that would play well with fixedTime but it's worth trying.