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Fix for 22822 ComputedStates example #23655

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alice-i-cecile merged 2 commits into from
Apr 6, 2026
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Fix for 22822 ComputedStates example #23655

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2f68730
Fix for 22822 ComputedStates example
scottgshannon Apr 4, 2026
2b36720
Update examples/state/computed_states.rs
scottgshannon Apr 4, 2026
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5 changes: 5 additions & 0 deletions examples/state/computed_states.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -54,6 +54,9 @@ impl ComputedStates for InGame {
// Our computed state depends on `AppState`, so we need to specify it as the SourceStates type.
type SourceStates = AppState;

// This is necessary to prevent `setup_game` from running when the app is already in `AppState::InGame`
// and only `paused` and `turbo` are changed
const ALLOW_SAME_STATE_TRANSITIONS: bool = false;
// The compute function takes in the `SourceStates`
fn compute(sources: AppState) -> Option<Self> {
// You might notice that InGame has no values - instead, in this case, the `State<InGame>` resource only exists
Expand All @@ -80,6 +83,7 @@ struct TurboMode;

impl ComputedStates for TurboMode {
type SourceStates = AppState;
const ALLOW_SAME_STATE_TRANSITIONS: bool = false;
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@kfc35 kfc35 Apr 4, 2026

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If you verify that you actually don’t need this line:

Suggested change
const ALLOW_SAME_STATE_TRANSITIONS: bool = false;

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@scottgshannon scottgshannon Apr 4, 2026

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TurboMode can be re-entered (via activating turbo then pausing). This produces duplicate UI elements that overlap and thus don't cause visual artifacts.

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@kfc35 kfc35 Apr 4, 2026

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Ah I see, I overlooked that, thank you for pointing that out


fn compute(sources: AppState) -> Option<Self> {
match sources {
Expand Down Expand Up @@ -107,6 +111,7 @@ enum IsPaused {

impl ComputedStates for IsPaused {
type SourceStates = AppState;
const ALLOW_SAME_STATE_TRANSITIONS: bool = false;
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@kfc35 kfc35 Apr 4, 2026

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If you verify that you actually don’t need this line:

Suggested change
const ALLOW_SAME_STATE_TRANSITIONS: bool = false;

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@scottgshannon scottgshannon Apr 4, 2026

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While IsPaused cannot be re-entered it is tied to an OnEnter system that performs command.spawn calls like the other computed states. This line could be removed and retain proper behavior but I believe the example is stronger by keeping it.


fn compute(sources: AppState) -> Option<Self> {
// Here we convert from our [`AppState`] to all potential [`IsPaused`] versions.
Expand Down