b35c6be8c9
Part of https://github.com/flutter/flutter/issues/152587 ### Description: With `withDurationAndBounce` (we could also rename to `withDuration`), the user only has to worry about a single attribute: the bounce (and duration, but they would have to worry with duration anyway. If they don't, there is a default value already). The standard `SpringDescription` has 3 values, so it is way more abstract. This should help a lot people to make beautiful spring animations using Flutter. <img width="838" alt="image" src="https://github.com/user-attachments/assets/4d0dccc7-0f97-4a13-99a4-268228b87f08" /> ### Negative bounce: I didn't enable bounce to be negative because the behavior is super tricky. I don't know what formula Apple is using, but seems like it is not public. There are many different formulas we can use, including the one provided on the original issue, but then there is the risk of people complaining it works differently than SwiftUI. I need to check if other projects (react-spring, framer motion) support negative bounce, but feels like this is something 99.9999% of people wouldn't expect or use, so I think we are safe. I couldn't find a single usage of negative bounce on Swift in all GitHub (without a duration, using code-search, vs 5k cases with positive values). Not even sure the todo is needed, but won't hurt. ### Comparison <details> <summary>Dart vs Swift testing results</summary> ```dart testWidgets('Spring Simulation Tests - Matching SwiftUI', (WidgetTester tester) async { // Test cases matching the Swift code's ranges List<({Duration duration, double bounce})> testCases = [ (duration: const Duration(milliseconds: 100), bounce: 0.0), (duration: const Duration(milliseconds: 100), bounce: 0.3), (duration: const Duration(milliseconds: 100), bounce: 0.8), (duration: const Duration(milliseconds: 100), bounce: 1.0), (duration: const Duration(milliseconds: 500), bounce: 0.0), (duration: const Duration(milliseconds: 500), bounce: 0.3), (duration: const Duration(milliseconds: 500), bounce: 0.8), (duration: const Duration(milliseconds: 500), bounce: 1.0), (duration: const Duration(milliseconds: 1000), bounce: 0.0), (duration: const Duration(milliseconds: 1000), bounce: 0.3), (duration: const Duration(milliseconds: 1000), bounce: 0.8), (duration: const Duration(milliseconds: 1000), bounce: 1.0), (duration: const Duration(milliseconds: 2000), bounce: 0.0), (duration: const Duration(milliseconds: 2000), bounce: 0.3), (duration: const Duration(milliseconds: 2000), bounce: 0.8), (duration: const Duration(milliseconds: 2000), bounce: 1.0), ]; for (final testCase in testCases) { SpringDescription springDesc = SpringDescription.withDurationAndBounce( duration: testCase.duration, bounce: testCase.bounce, ); print( 'Duration: ${testCase.duration.inMilliseconds / 1000}, Bounce: ${testCase.bounce}, Mass: ${springDesc.mass}, Stiffness: ${springDesc.stiffness}, Damping: ${springDesc.damping}', ); } }); ``` Output: ``` Duration: 0.1, Bounce: 0.0, Mass: 1.0, Stiffness: 3947.8417604357423, Damping: 125.66370614359171 Duration: 0.1, Bounce: 0.3, Mass: 1.0, Stiffness: 3947.8417604357423, Damping: 87.9645943005142 Duration: 0.1, Bounce: 0.8, Mass: 1.0, Stiffness: 3947.8417604357423, Damping: 25.132741228718338 Duration: 0.1, Bounce: 1.0, Mass: 1.0, Stiffness: 3947.8417604357423, Damping: 0.0 Duration: 0.5, Bounce: 0.0, Mass: 1.0, Stiffness: 157.91367041742973, Damping: 25.132741228718345 Duration: 0.5, Bounce: 0.3, Mass: 1.0, Stiffness: 157.91367041742973, Damping: 17.59291886010284 Duration: 0.5, Bounce: 0.8, Mass: 1.0, Stiffness: 157.91367041742973, Damping: 5.026548245743668 Duration: 0.5, Bounce: 1.0, Mass: 1.0, Stiffness: 157.91367041742973, Damping: 0.0 Duration: 1.0, Bounce: 0.0, Mass: 1.0, Stiffness: 39.47841760435743, Damping: 12.566370614359172 Duration: 1.0, Bounce: 0.3, Mass: 1.0, Stiffness: 39.47841760435743, Damping: 8.79645943005142 Duration: 1.0, Bounce: 0.8, Mass: 1.0, Stiffness: 39.47841760435743, Damping: 2.513274122871834 Duration: 1.0, Bounce: 1.0, Mass: 1.0, Stiffness: 39.47841760435743, Damping: 0.0 Duration: 2.0, Bounce: 0.0, Mass: 1.0, Stiffness: 9.869604401089358, Damping: 6.283185307179586 Duration: 2.0, Bounce: 0.3, Mass: 1.0, Stiffness: 9.869604401089358, Damping: 4.39822971502571 Duration: 2.0, Bounce: 0.8, Mass: 1.0, Stiffness: 9.869604401089358, Damping: 1.256637061435917 Duration: 2.0, Bounce: 1.0, Mass: 1.0, Stiffness: 9.869604401089358, Damping: 0.0 ``` Swift: ```swift import SwiftUI import XCTest class SpringParameterTests: XCTestCase { func printSpringParameters(duration: Double, bounce: Double) { let spring = Spring(duration: duration, bounce: bounce) // Let SwiftUI do its thing print("Duration: \(duration), Bounce: \(bounce), Mass: \(spring.mass), Stiffness: \(spring.stiffness), Damping: \(spring.damping)") } func testParameterExtraction() { // Test a range of durations and bounces let durations: [Double] = [0.1, 0.5, 1.0, 2.0] let bounces: [Double] = [0.0, 0.3, 0.8, 1.0] for duration in durations { for bounce in bounces { printSpringParameters(duration: duration, bounce: bounce) } } } } ``` Output: ``` Duration: 0.1, Bounce: 0.0, Mass: 1.0, Stiffness: 3947.8417604357433, Damping: 125.66370614359172 Duration: 0.1, Bounce: 0.3, Mass: 1.0, Stiffness: 3947.841760435743, Damping: 87.96459430051421 Duration: 0.1, Bounce: 0.8, Mass: 1.0, Stiffness: 3947.8417604357423, Damping: 25.132741228718338 Duration: 0.1, Bounce: 1.0, Mass: 1.0, Stiffness: 3947.8417604357433, Damping: 0.0 Duration: 0.5, Bounce: 0.0, Mass: 1.0, Stiffness: 157.91367041742973, Damping: 25.132741228718345 Duration: 0.5, Bounce: 0.3, Mass: 1.0, Stiffness: 157.9136704174297, Damping: 17.59291886010284 Duration: 0.5, Bounce: 0.8, Mass: 1.0, Stiffness: 157.9136704174297, Damping: 5.026548245743668 Duration: 0.5, Bounce: 1.0, Mass: 1.0, Stiffness: 157.91367041742973, Damping: 0.0 Duration: 1.0, Bounce: 0.0, Mass: 1.0, Stiffness: 39.47841760435743, Damping: 12.566370614359172 Duration: 1.0, Bounce: 0.3, Mass: 1.0, Stiffness: 39.478417604357425, Damping: 8.79645943005142 Duration: 1.0, Bounce: 0.8, Mass: 1.0, Stiffness: 39.478417604357425, Damping: 2.513274122871834 Duration: 1.0, Bounce: 1.0, Mass: 1.0, Stiffness: 39.47841760435743, Damping: 0.0 Duration: 2.0, Bounce: 0.0, Mass: 1.0, Stiffness: 9.869604401089358, Damping: 6.283185307179586 Duration: 2.0, Bounce: 0.3, Mass: 1.0, Stiffness: 9.869604401089356, Damping: 4.39822971502571 Duration: 2.0, Bounce: 0.8, Mass: 1.0, Stiffness: 9.869604401089356, Damping: 1.256637061435917 Duration: 2.0, Bounce: 1.0, Mass: 1.0, Stiffness: 9.869604401089358, Damping: 0.0 ``` There are minor differences which should be rounding errors. </details>
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