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## Objective Currently, events are dropped after two frames. This cadence wasn't *chosen* for a specific reason, double buffering just lets events persist for at least two frames. Events only need to be dropped at a predictable point so that the event queues don't grow forever (i.e. events should never cause a memory leak). Events (and especially input events) need to be observable by systems in `FixedUpdate`, but as-is events are dropped before those systems even get a chance to see them. ## Solution Instead of unconditionally dropping events in `First`, require `FixedUpdate` to first queue the buffer swap (if the `TimePlugin` has been installed). This way, events are only dropped after a frame that runs `FixedUpdate`. ## Future Work In the same way we have independent copies of `Time` for tracking time in `Main` and `FixedUpdate`, we will need independent copies of `Input` for tracking press/release status correctly in `Main` and `FixedUpdate`. -- Every run of `FixedUpdate` covers a specific timespan. For example, if the fixed timestep `Δt` is 10ms, the first three `FixedUpdate` runs cover `[0ms, 10ms)`, `[10ms, 20ms)`, and `[20ms, 30ms)`. `FixedUpdate` can run many times in one frame. For truly framerate-independent behavior, each `FixedUpdate` should only see the events that occurred in its covered timespan, but what happens right now is the first step in the frame reads all pending events. Fixing that will require timestamped events. --------- Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com> |
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Bevy Time
The built-in timekeeping plugin for the Bevy game engine.