[Merged by Bors] - Redo State architecture #1424

TheRawMeatball · 2021-02-09T20:46:33Z

An alternative to StateStages that uses SystemSets. Also includes pop and push operations since this was originally developed for my personal project which needed them.

Ratysz · 2021-02-10T18:02:45Z

Suggested changes from Discord earlier: SetState -> State (assuming StateStage is removed); StateSetBuilder -> StateSet; remove ScheduledOperation, split schedule_operation() into three methods.

Speaking of StateStage: since this is more or less a replacement, might be a good idea to try removing it now as well.

I'm not sure I like the admittedly clever hack with state_cleaner: it hides from the user what's actually going on. If I were to use this, I would definitely try it via regular system sets with state-related run criteria and assume the state would be driven... somehow. This is why I keep suggesting that state-driving system should be required to be added explicitly, by the user; there is just too many edge cases to try and cover for all of them automatically without being implicit somewhere.

TheRawMeatball · 2021-02-10T20:47:13Z

Hmm, I agree with most of your points but I'd argue keeping state_cleaner a hidden implementation detail is the better choice: I feel like adding a state should automatically add all necessary parts, including the driver. As an improvement I might make soon, this impl can probably be improved by automatically adding in relations between the driver system and all systems in the driven sets to remove the need for the hard sync point. If the state driver was to be manual, this burden would be on the user, and I don't think thats very elegant.

Ratysz · 2021-02-10T21:02:05Z

I am insinuating that this approach relies on its own abstraction, rather than integrating well with existing ones. How will this interoperate with plain system sets (i.e. what if something uses the provided run criteria without going through StateSet)? With states being used across stages? How will this work with #1375?

That said, the improvement you're planning will, in my opinion, make this a very good direct replacement to StateStage until at least the time we figure out the questions above.

As for epithets, "elegant" is when things work out beautifully and with perfect clarity; this idea strikes me as "sneaky" at best - which doesn't mean it's bad.

TheRawMeatball · 2021-02-11T08:00:15Z

Alright, I cleaned up the API and made it more aligned with the rest of the ECS. I'll update the example when #1428 is merged.

TheRawMeatball · 2021-02-15T16:38:29Z

Ok, the PR is ready except for the examples, which I'll fix after #1453

crates/bevy_ecs/src/schedule/state.rs

Ratysz · 2021-02-15T16:55:36Z

crates/bevy_ecs/src/schedule/state.rs

@@ -61,6 +67,9 @@ impl<T: Clone + Resource> State<T> {
        Wrapper::<T, OnExit>::new(discriminant(&d))
    }

+    /// Creates a driver set for the State.
+    ///
+    /// Important note: this set must be inserted **before** all other state-dependant sets to work properly!


This is unfortunate, but I don't think this can be avoided until #1375 or some stop-gap measure that lets us order run criteria evaluation.

crates/bevy_app/src/app_builder.rs

crates/bevy_ecs/src/schedule/state.rs

Co-authored-by: bjorn3 <bjorn3@users.noreply.github.com>

crates/bevy_ecs/src/schedule/state.rs

alice-i-cecile

This seems like a very solid improvement to StateStages: the way it's decoupled makes much more sense and the general API seems sensible. Are there any good patterns for working with compound states with this API? If so, they likely deserve their own example.

alice-i-cecile · 2021-03-08T20:19:30Z

crates/bevy_app/src/app_builder.rs

-        })
+    pub fn add_state<T: Component + Clone + Eq>(&mut self, initial: T) -> &mut Self {
+        self.insert_resource(State::new(initial))
+            .add_system_set(State::<T>::make_driver())


Is it possible to add these system sets (and hence states) to stages other than Update?

add_state_to_stage is the solution for this.

alice-i-cecile · 2021-03-08T20:22:36Z

examples/game/alien_cake_addict.rs

-            scoreboard_system.system(),
+        .add_system_set(State::on_enter_set(GameState::Playing).with_system(setup.system()))
+        .add_system_set(
+            State::on_update_set(GameState::Playing)


on_enter_set and friends is a bit of a confusing name in English: "set" could either be a verb (to set a property on update...) or a "noun" (a collection of systems). I think it's the latter here from context.

IMO State::on_enter (etc.) would be clearer in typical usage, since you're seeing the system set call just above it already.

Ah I see, those names are reserved for the transition functions...

What about on_enter_systems?

I don't feel strongly either way, so sure.

I think I like this:

.add_system_set(SystemSet::on_enter(GameState::Playing).with_system(setup.system()))

more than this:

.add_system_set(State::on_enter_set(GameState::Playing).with_system(setup.system()))

Normally I would prefer the current impl as it's a clean "layer" on top of system sets, but SystemSet::on_enter reads better and is clearer about the type. The fact that they are in the same module also makes me feel better about it.

alice-i-cecile · 2021-03-08T20:35:58Z

crates/bevy_ecs/src/schedule/state.rs

-        let stages = self.state_stages(state);
-        stages.enter = Box::new(stage);
-        self
+    pub fn on_inactive_update(s: T) -> impl System<In = (), Out = ShouldRun> {


Could we have a doc string describing this function? It's not clear from either the name or a quick look at the code.

Hmm, documentation on the various on_*_set methods is a good idea, though I'd probably put the actual docs on on_* and link.

cart · 2021-03-11T23:27:16Z

examples/game/alien_cake_addict.rs

-            scoreboard_system.system(),
+        .add_system_set(State::on_enter_set(GameState::Playing).with_system(setup.system()))
+        .add_system_set(
+            State::on_update_set(GameState::Playing)


I think I like this:

.add_system_set(SystemSet::on_enter(GameState::Playing).with_system(setup.system()))

more than this:

.add_system_set(State::on_enter_set(GameState::Playing).with_system(setup.system()))

Normally I would prefer the current impl as it's a clean "layer" on top of system sets, but SystemSet::on_enter reads better and is clearer about the type. The fact that they are in the same module also makes me feel better about it.

crates/bevy_ecs/src/schedule/state.rs

cart · 2021-03-15T22:11:47Z

bors r+

An alternative to StateStages that uses SystemSets. Also includes pop and push operations since this was originally developed for my personal project which needed them.

bors · 2021-03-15T22:36:25Z

Pull request successfully merged into main.

Build succeeded:

zicklag · 2021-03-16T00:26:42Z

Thank you for this @TheRawMeatball !! Me and my brother were literally just talking about how we felt like state could be simpler and then a couple hours later this is merged. It's great!

Implement StateSet

a9d4f55

TheRawMeatball force-pushed the state-set-v2 branch from 091f5a8 to a9d4f55 Compare February 9, 2021 20:55

TheRawMeatball marked this pull request as draft February 9, 2021 20:59

ci fix

4c4f795

Improve API and remove StateStage

ff6ed69

TheRawMeatball added 3 commits February 11, 2021 11:05

Fix bevy_app

ca54b6e

Minor cleanup

f1073f5

Major improvements

49adf8e

Ratysz reviewed Feb 15, 2021

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TheRawMeatball added 3 commits February 16, 2021 11:16

Fix startup bug

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Add InStackUpdate

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Fix unit test

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alice-i-cecile added A-ECS Entities, components, systems, and events help wanted labels Feb 17, 2021

Ratysz mentioned this pull request Feb 17, 2021

Make current state a property of StateStage #1125

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TheRawMeatball mentioned this pull request Feb 17, 2021

'enter' stage not called in some cases #1117

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TheRawMeatball added 2 commits February 19, 2021 21:02

Arbitrarily typed states

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Removed redundant allow

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Base automatically changed from master to main February 19, 2021 20:44

TheRawMeatball added 5 commits March 5, 2021 11:38

Merge branch 'main' into state-set-v2

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Update State

c1f6079

hotfix

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Finalize

d0065f2

Finish

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TheRawMeatball changed the title ~~Implement State sets~~ Redo State architecture Mar 5, 2021

TheRawMeatball marked this pull request as ready for review March 5, 2021 16:32

bjorn3 reviewed Mar 5, 2021

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crates/bevy_ecs/src/schedule/state.rs Outdated Show resolved Hide resolved

Update crates/bevy_ecs/src/schedule/state.rs

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Co-authored-by: bjorn3 <bjorn3@users.noreply.github.com>

bjorn3 reviewed Mar 5, 2021

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TheRawMeatball added 3 commits March 5, 2021 19:53

Remove unnecessary /**/

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Improve API ergonomics

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Hotfix

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alice-i-cecile reviewed Mar 8, 2021

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This was referenced Mar 8, 2021

Add remaining State Chart functionalities to States #1597

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0.4 -> 0.5 Migration Guide #1601

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cart reviewed Mar 12, 2021

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Fix same-state transitions

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TheRawMeatball added 3 commits March 14, 2021 10:02

Cut down on explicit ordering

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Merge branch 'main' into state-set-v2

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cargo fmt

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cart added this to the Bevy 0.5 milestone Mar 15, 2021

TheRawMeatball added 2 commits March 16, 2021 00:16

Remove unnecessary println!

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Final issues

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bors bot pushed a commit that referenced this pull request Mar 15, 2021

Redo State architecture (#1424)

284889c

An alternative to StateStages that uses SystemSets. Also includes pop and push operations since this was originally developed for my personal project which needed them.

bors bot changed the title ~~Redo State architecture~~ [Merged by Bors] - Redo State architecture Mar 15, 2021

bors bot closed this Mar 15, 2021

TheRawMeatball deleted the state-set-v2 branch March 15, 2021 22:39

This was referenced Mar 17, 2021

State-dependent system runs twice on wrong add_state call order #1672

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[Merged by Bors] - Fix panic in multiple_windows example #1737

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[Merged by Bors] - Redo State architecture #1424

[Merged by Bors] - Redo State architecture #1424

TheRawMeatball commented Feb 9, 2021

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zicklag commented Mar 16, 2021

[Merged by Bors] - Redo State architecture #1424

[Merged by Bors] - Redo State architecture #1424

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