flip_layout 0.2.0-dev.1

Declarative layout & presence animations — enter/exit + FLIP reflow for any layout. A Framer Motion for Flutter.

0.2.0-dev.1

Prerelease of the 0.2.0 line for testing on pub.dev before the stable cut.

• New: MotionSpring — a velocity-preserving spring for position slides. Unlike SpringCurve (a fixed-duration spring look), it drives the slide with a live SpringSimulation on an unbounded controller, so a re-order mid-slide carries the element's momentum into the new target. Wire it via a new spring: argument on LayoutMotion/MotionGroup, or a spring: default on MotionConfig. SpringCurve still works for the simple curve path.
• New: shared-element flight polish — MotionSharedScope.flightShuttleBuilder (render a fully custom in-flight widget, given the source and destination children + the flight animation) and MotionSharedScope.crossFade (the built-in flight dissolves source→destination instead of carrying only the destination child). The example Shared tab now cross-fades tile→detail.
• New: MotionGroup lifecycle + exit stagger — onEnter(key) / onExitComplete(key) callbacks and an exitStagger so a batch of leaving children cascade out one-after-another. The example Add/remove tab shows both (a "Clear" button + a live status line).
• New: large-collection guard — MotionGroup prints a one-time debug warning when its child count exceeds MotionGroup.debugChildCountWarningThreshold (default 150), since it isn't virtualised. README/SPEC steer big lists to AnimatedList / SliverAnimatedList.
• Docs: documented the shared-element birth-order heuristic and its limits in doc/ARCHITECTURE.md; SPEC/ROADMAP/README updated for the above.
• Tests: added coverage for the flight shuttle + cross-fade, three-holder birth-order pick, rapid open/close and flight-interrupted-by-flight, spring slide + velocity-continuous re-target, the large-count warning, and the lifecycle callbacks + exit stagger.
• All public API additions are backward compatible with 0.1.x.

0.1.0

• New: MotionSharedScope + MotionSharedId — shared-element "magic move" transitions within a page (grid→detail, list→hero) with no route change, the thing Flutter's Hero only does across routes. Example gains a Shared tab.
• New: SpringCurve — a tunable spring (mass/stiffness/damping) as a Curve, for overshoot-and-settle slides anywhere a curve is accepted.
• New: MotionConfig — set duration/curve/stagger defaults for a subtree once, and honour reduced-motion (config flag, or the OS accessibility setting automatically) by skipping animations. LayoutMotion/MotionGroup duration/curve/stagger are now nullable and inherit from it.
• New: MotionGroup.exitTransitionBuilder — give leaving children a different transition from entering ones.
• New: LayoutMotion slides are now interruptible — a layout change mid-slide re-targets from the current on-screen position instead of snapping to 0, so rapid reorders/filters stay smooth (also benefits MotionGroup).
• New: MotionGroup — a declarative collection animator that does enter/exit (an AnimatePresence equivalent) + layout (FLIP) in any layout (Wrap, GridView, Column, …). Just change the children list. Supports stagger, animateInitial, and a custom transitionBuilder.
• Example: redesigned around MotionGroup — Filter (a Wrap that no built-in animates), Reorder (FLIP + stagger), and Add/remove (enter/exit). The old Expand demo was removed (that's AnimatedSize/ExpansionTile's job, and mixing FLIP with a continuous resize caused jitter). Runs on web; deep-linkable via ?demo=<id>.
• Docs: README repositioned around MotionGroup with screenshots and a "When not to use this" section; docs/ renamed to doc/ (pub convention); added pubspec topics.
• Bundles all 0.0.2 fixes below.

0.0.2

• Fix: measurement now reads the untransformed layout position (via a MetaData proxy above the Transform), so an in-flight animation no longer contaminates the next measurement — eliminates jitter/oscillation.
• Fix: inside a Scrollable, positions are measured in scroll content space, so plain scrolling no longer triggers spurious slide animations.
• Fix: the resting transform settles exactly to identity on completion.
• Fix: degenerate (zero-size / offstage) transitions are skipped instead of animating a bogus delta.
• API: added onEnd callback; AnimatedLayout forwards animateSize and asserts each wrapped child has a key.
• Docs: added docs/SPEC.md; added tests for the FLIP inverse, scroll invariance, the key assertion, and onEnd.

0.0.1

• Initial scaffold: LayoutMotion widget (FLIP-based auto layout animation) and AnimatedLayout convenience wrapper.