[][src]Crate ftvf

ftvf is a crate for carrying out game logic the One True Way: Fixed Tickrate, Variable Framerate. By having your game logic in strictly fungible ticks, rather than having it vary based on framerate, you gain many advantages:

  • Repeatability: the same inputs will have the same outputs, period.
  • Framerate independence: no issues like Quake had where your exact jump height depends on how fast your computer is.
  • Satisfaction: knowing that you made the morally correct choice. :)

To get started, add ftvf to your dependencies in Cargo.toml:

ftvf = "0.5"

then initialize yourself a Metronome:

let mut metronome = Metronome::new(RealtimeNowSource::new(),
                                   (30, 1), // want 30 ticks per 1 second
                                   5); // accept being up to 5 ticks behind

And then your game loop looks like this:

while !world.should_quit() {
  // call `sample` once per batch. not zero times, not two or more times!
  while let Some(status) = metronome.status(Mode::UnlimitedFrames) {
    match status {
      Status::Tick => world.perform_tick(),
      Status::Frame{phase} => world.render(phase),
        => eprintln!("Warning: time flowed backwards!"),
        => eprintln!("Warning: we're too slow, lost {} ticks!", n),
      // No special handling or warning message is needed for Rollover. In
      // practice, it will never be seen.
      Status::Rollover => (),
      // Mode::UnlimitedFrames never returns Idle, but other modes can, and
      // this is the way it should be handled.
      Status::Idle => metronome.sleep_until_next_tick(),

Your logic ticks operate in discrete, fixed time intervals. Then, when it comes time to render, you render a frame which represents time some portion of the way between two ticks, represented by its phase. Your rendering process should render an interpolated state between the previous tick and the current tick, based on the value of phase. Simple example:

               + (self.current_position - self.previous_position) * phase);


ftvf is distributed under the zlib license. The complete text is as follows:

Copyright (c) 2019, Solra Bizna

This software is provided "as-is", without any express or implied warranty. In no event will the author be held liable for any damages arising from the use of this software.

Permission is granted to anyone to use this software for any purpose, including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgement in the product documentation would be appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.



The meat of the crate. Contains all state necessary to turn pure temporal chaos into an orderly stream of ticks and frames.


A NowSource that uses the standard Rust timing facilities to obtain its timing information. This is the default NowSource, and also the one you almost certainly want to use.



How ticks and frames should relate to one another in a given call to Metronome::status.


Time handling information returned by a Metronome.



A source of time information for Metronome to use. For most purposes, RealtimeNowSource will be sufficient.