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perf!: skip widget rebuilds during divider drag#134

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optimize-animated-builder
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perf!: skip widget rebuilds during divider drag#134
andyhorn wants to merge 6 commits into
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optimize-animated-builder

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@andyhorn andyhorn commented May 27, 2026 •
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Summary

  • Splits ResizableController's notification surface: drag/post-layout pixel updates flow through a new pixelsListenable (ValueListenable<List<double>>); the main controller listener fires only on structural changes.
  • ResizableLayoutRenderObject subscribes to the pixel listenable and markNeedsLayouts on change. The widget tree above is never rebuilt during a drag — only performLayout runs.
  • ResizableContainer replaces AnimatedBuilder with ListenableBuilder, drops _flexFromFullSizes for the idle phase (still used for hide-animation phases), and wraps each child in RepaintBoundary.
  • RTL offset reversal moves into the render object since the live path no longer goes through Flex.

Closes #120.

Breaking change

ResizableController.addListener(...) no longer fires on divider drag — it now fires only on structural changes (children list, declared sizes, hidden set, layout invalidation). Callers that watched the controller for live size changes should subscribe to controller.pixelsListenable instead.

- controller.addListener(() => print(controller.pixels));
+ controller.pixelsListenable.addListener(() => print(controller.pixelsListenable.value));

Test plan

  • All 158 unit/widget tests pass.
  • New rebuild-count test asserts zero child rebuilds and zero main-controller-listener firings during a drag.
  • New render-object tests cover the live-pixel path, the cold ↔ live transition, the listenable swap, RTL reversal, and hidden-divider collapse.
  • New controller tests cover the four notification sites (adjustChildSize, setRenderedSizes, setSizes, setHidden, setChildren) and disposal semantics.
  • Smoke-test in the example app.

🤖 Generated with Claude Code

andyhorn added a commit that referenced this pull request May 27, 2026
@andyhorn
refactor: snapshot pixelsListenable + tighten contract docs
3d4b65c 
Address review findings on PR #134:

- Replace `_PixelsListenable` wrapper with a `ValueNotifier<List<double>>`
  that publishes a fresh `UnmodifiableListView` snapshot per notification,
  restoring proper `ValueListenable` old/new comparison semantics.
- Push a fresh snapshot from `_setAvailableSpace` so the live-pixel render
  path sees redistributed pixels after a LayoutBuilder-driven rebuild.
- Rewrite the `pixelsListenable` dartdoc: drop private-symbol references
  and the negative contract, add a migration note for callers that watched
  the controller for size changes.
- Acknowledge in the controller class doc that the main listener also fires
  on the post-layout rendered-size update.
- Update the README size-tracking snippet to use `pixelsListenable`.
- Assert `constraints.maxWidth.isFinite` in the RTL horizontal reversal
  path now that the assumption is no longer enforced by a `Flex` parent.
- Add tests: `show()` notification, render-object detach/reattach lifecycle,
  vertical-axis rebuild and live-pixel coverage, and the `_canUseLivePixels`
  length-mismatch cold-path fallback.
andyhorn and others added 5 commits May 27, 2026 21:24
@andyhorn @claude
perf!: skip widget rebuilds during divider drag
e8e9ce4 
Replaces the per-tick ChangeNotifier-driven rebuild of the entire
container subtree with a render-object listener on a dedicated pixel
channel. Drag updates now relayout the children directly without
rebuilding any widgets.

* `ResizableController` exposes `pixelsListenable` — a
  `ValueListenable<List<double>>` that fires on every pixel change
  (drag, post-layout, structural). The main controller listener no
  longer fires during a drag.
* `ResizableLayoutRenderObject` accepts the listenable, subscribes
  on attach, and `markNeedsLayout`s on change. `performLayout`
  branches: when the listenable is present, lay out children
  directly from its value (fast path); otherwise resolve from the
  declared sizes (cold path) and report the resolved values via
  `onComplete`.
* `ResizableContainer` replaces its outer `AnimatedBuilder` with
  `ListenableBuilder` and drops `_flexFromFullSizes` for the idle
  phase; hide-animation phases continue to use the flex path. Each
  child is wrapped in `RepaintBoundary` so paint dirtiness doesn't
  propagate to siblings during a drag.
* RTL offset reversal moves into the render object, since the live
  path no longer goes through `Flex`.

BREAKING CHANGE: `ResizableController`'s `addListener` no longer
fires on divider drag updates — it now fires only on structural
changes (children list, declared sizes, hidden set, layout
invalidation). Callers that watched the controller for live size
changes should subscribe to `controller.pixelsListenable` instead.

Closes #120

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
@andyhorn
refactor: snapshot pixelsListenable + tighten contract docs
d793bcb 
Address review findings on PR #134:

- Replace `_PixelsListenable` wrapper with a `ValueNotifier<List<double>>`
  that publishes a fresh `UnmodifiableListView` snapshot per notification,
  restoring proper `ValueListenable` old/new comparison semantics.
- Push a fresh snapshot from `_setAvailableSpace` so the live-pixel render
  path sees redistributed pixels after a LayoutBuilder-driven rebuild.
- Rewrite the `pixelsListenable` dartdoc: drop private-symbol references
  and the negative contract, add a migration note for callers that watched
  the controller for size changes.
- Acknowledge in the controller class doc that the main listener also fires
  on the post-layout rendered-size update.
- Update the README size-tracking snippet to use `pixelsListenable`.
- Assert `constraints.maxWidth.isFinite` in the RTL horizontal reversal
  path now that the assumption is no longer enforced by a `Flex` parent.
- Add tests: `show()` notification, render-object detach/reattach lifecycle,
  vertical-axis rebuild and live-pixel coverage, and the `_canUseLivePixels`
  length-mismatch cold-path fallback.
@andyhorn
refactor!: split needsLayout signal from main controller listener
05ed444 
Expose `ResizableController.needsLayoutListenable: ValueListenable<bool>`,
which fires when the controller's `needsLayout` flag transitions. The
container now subscribes to this listenable alongside the controller via
`Listenable.merge`, decoupling the cold↔live build-path swap from the
main listener.

With this in place, `_setRenderedSizes` no longer calls `notifyListeners`.
The main controller listener is now reserved strictly for structural
changes (children list, declared sizes, hidden set); post-layout updates
flow through `needsLayoutListenable` (for the build-path swap) and
`pixelsListenable` (for the rendered pixel values).

Breaking: callers that watched the controller via `addListener` to react
to *any* post-layout state change now see fires only on structural events.
Subscribe to `needsLayoutListenable` for layout-state transitions or to
`pixelsListenable` for live pixel values.

Update the `notify count` tests in `resizable_container_test.dart` to
assert the new contract on both listenables.
@andyhorn @claude
test: pin listener contracts for main/pixels/needsLayout listenables
5759fc8 
Cover the three-listenable surface from a consumer's POV: main
ChangeNotifier fires only on structural changes, pixelsListenable carries
drag updates and snapshot-stable values, needsLayoutListenable tracks
build-path swap. Also pins the Listenable.merge coalescing the container
relies on and the README migration pattern.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
@andyhorn @claude
test: cover clamping, hide-animation, and lifecycle for the live path
c1c2316 
- Pin that drag clamping happens in the controller before publishing to
  pixelsListenable, not in the render-object live layout. A documenting
  test asserts the live layout renders constraint-violating pixels
  verbatim, so any future re-clamping there fails loudly.
- Pin the hide/show animation contract under the new dual-listenable
  surface: pixelsListenable fires a bounded number of times per
  hide/show (the animation lives in HideAnimationCoordinator, not the
  controller, so it is not per-frame), main listener fires exactly once
  per call, and a concurrent drag does not bump main.
- Pin controller swap via didUpdateWidget (old detached, new attached,
  consumer-owned), late subscriber delivery, dispose ordering, and the
  documented multi-container-sharing limitation (each initChildren wipes
  hidden indices, so containers cannot share a controller).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
@andyhorn andyhorn force-pushed the optimize-animated-builder branch from c84543f to c1c2316 Compare May 28, 2026 04:24
@andyhorn @claude
fix: honor divider lock state on the live build path
b9b0c5b 
The perf live path built dividers without the enabled flag, so locked
dividers (resizable: false or ResizableDivider.enabled: false) still
responded to drag, tap, and hover. Pass enabled through to match the
hide-animation path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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AnimatedBuilder rebuilds the whole subtree on every drag tick

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@andyhorn