menu example panics with `can not convert float seconds to Duration: value is negative`

[djeedai]

@Gyrobifastigium FYI this is probably a bug in #39

This is blocking #34

[Gyrobifastigium]

The panic happens because:

• The Delay tween in the example has a 0-duration self.timer, so self.timer.percent() returns NaN.
• As a result, tween.progress() returns NaN.
• As a result, tween.duration().mul_f32(1.0 - tween.progress()) panics.

I feel like Delay::progress() should yield 1.0 (or 0.0) for a 0-duration timer, but that would require special-casing.

EDIT: I guess any return value between 0.0 and 1.0 would be "technically true" and would make the math work in Sequence::tick because it gets multiplied by tween.duration() (aka 0) anyways. An elapsed-based API would circumvent the issue.

[SUPERCILEX]

If that's the case, then this will almost certainly be fixed by #38.

Sitenote: #39 is probably going to get reverted since we're rewriting tracks and sequences.

[SUPERCILEX]

Nevermind, not fixed by #38 because progress is still implemented the same way.

Though as mentioned, tick needs to be rewritten anyway to not use progress so this will go away.

[SUPERCILEX]

Note to self: write a test for this when rewriting sequences.

[Gyrobifastigium]

I don't know if this should go in a separate issue, but somehow in my game where I'm using a fork of bevy_tweening v0.4 with #39 applied, I just got a panic on the line delta -= tween_remaining. That shouldn't be possible unless some invariant in the tween API (between duration(), progress(), and tick()) is broken -- maybe as a result of floating point / rounding error.

As a workaround, I'm changing the line to delta = delta.saturating_sub(tween_remaining) in my fork for now.

[djeedai]

Interesting. What's the panic about exactly? Is delta becoming negative?

[Gyrobifastigium]

Yes, it is. I've only seen it happen once so it seems to be pretty rare.

[shuoli84]

In my case, it is not rare, I hit by the panic each time run

RUST_BACKTRACE=1 cargo run --example menu --features="bevy/bevy_winit"

[shuoli84]

A work around, set start_time_ms to a small value, e.g

    let mut start_time_ms = 10;

[benfrankel]

In my case, it is not rare, I hit by the panic each time run

RUST_BACKTRACE=1 cargo run --example menu --features="bevy/bevy_winit"

I assume you're referring to the "can not convert float seconds to Duration: value is negative" panic (original panic mentioned in this issue, guaranteed to occur in the menu example), and not the "overflow when subtracting durations" panic (mentioned in #41 (comment), seen rarely in other code).

[shuoli84]

@benfrankel ah, yeah, different panic, "'can not convert float seconds to Duration: value is either too big or NaN'"