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fix:withDecay animation not starting if inital value is set to 0 #6769

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fix:withDecay animation not starting if inital value is set to 0 #6769

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25b84c4
Fix `withDecay` animation not running when sharedValue is 0
patrycjakalinska Nov 27, 2024
b07255a
Merge branch 'main' into @patrycjakalinska/with-decay-never-start-issue
patrycjakalinska Dec 13, 2024
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1 change: 1 addition & 0 deletions packages/react-native-reanimated/src/animation/decay/decay.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -113,6 +113,7 @@ export const withDecay = function (
onFrame: decay,
onStart,
callback,
forceRunAnimation: true,
velocity: config.velocity ?? 0,
initialVelocity: 0,
current: 0,
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Instead of adding that artificial prop, we should calculate the finish position like we do for withTiming, for example. You can see how it's done here: https://github.com/software-mansion/react-native-reanimated/blob/main/packages/react-native-reanimated/src/animation/timing.ts#L154. This solution should be clearer and simpler

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As I can see timing doesn't rely on previous current to calculate recent current value, as the decay does it. Wouldn't setting current in onStart to toValue break for example this decay function fragment:

  animation.current = current + (v * config.velocityFactor * deltaTime) / 1000;

Just wondering, because even this fragment can be rewritten to support your idea (so not a problem really)

In conclusion, to fully understand, you want to replace the current with toValue instead of - in this case - 0, so that it will not go into this conditional?

    if (
      mutable._value === animation.current &&
      !animation.isHigherOrder &&
      !forceUpdate
    ) {
      animation.callback && animation.callback(true);
      return;
    }

Should I also mark it as a isHigherOrder as it will hold its target value in .current?

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9 changes: 8 additions & 1 deletion packages/react-native-reanimated/src/animation/decay/utils.ts
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Expand Up @@ -13,16 +13,23 @@ const IS_WEB = isWeb();
export const VELOCITY_EPS = IS_WEB ? 1 / 20 : 1;
export const SLOPE_FACTOR = 0.1;

/*
* The `forceRunAnimation` prop is necessary to run withDecay animation when
* related sharedValue stays as `0`. It allows to skip animation check and start
* animation immediately
*/

export interface DecayAnimation extends Animation<DecayAnimation> {
lastTimestamp: Timestamp;
startTimestamp: Timestamp;
initialVelocity: number;
velocity: number;
current: AnimatableValue;
forceRunAnimation: boolean;
}

export interface InnerDecayAnimation
extends Omit<DecayAnimation, 'current'>,
extends Omit<DecayAnimation, 'current' | 'forceRunAnimation'>,
AnimationObject {
current: number;
springActive?: boolean;
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1 change: 1 addition & 0 deletions packages/react-native-reanimated/src/valueSetter.ts
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Expand Up @@ -31,6 +31,7 @@ export function valueSetter<Value>(
// built in animations that are not higher order(withTiming, withSpring) hold target value in .current
if (
mutable._value === animation.current &&
!animation.forceRunAnimation &&
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it seems like this check has a purpose (explained above), does introducing this flag not defeat that purpose? i think this needs to be rethought more holistically with the above comment in mind

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to be clear i'm not a maintainer, just thinking based on the code

!animation.isHigherOrder &&
!forceUpdate
) {
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