Flutter: draw only when the artboard changed (didChange), like iOS and web #665

Submission checklist

• I have confirmed the issue is present in the latest version of the rive Flutter package
• I have searched the documentation and forums and could not find an answer
• I have searched existing issues and this is not a duplicate

Description

With Factory.flutter, FlutterRiveRenderBox calls markNeedsPaint() after every ticker advance while advance returns true; whether the artboard changed is never checked. The C++ runtime already tracks it (Artboard::didChange()), and the other runtimes use it:

• iOS: RiveView.drawOptimization: DrawOptimization { alwaysDraw, drawOnChanged } (default .drawOnChanged).
• Web: drawingOptions: DrawOptimizationOptions { AlwaysDraw, DrawOnChanged } (default DrawOnChanged).

Flutter doesn't even expose the flag, so any animation that keeps advancing redraws every frame, including frames where nothing changed.

Patch (ready to re-land)

rive_native has no public repo for a PR, so the series is on a fork, based on rive_native 0.2.0-dev.3 verbatim from pub.dev (4 commits, offered for re-landing with co-authorship as for #631):

• Michael-Betclic/rive_native@main...draw-on-changed (.patch)

What it does:

• Exports riveArtboardDidChange and adds Artboard.didChange (looked up optionally: binaries without it return true, i.e. always draw).
• Adds DrawOptimization { alwaysDraw, drawOnChanged } on ProceduralPainter, same names as iOS. Default alwaysDraw = unchanged behaviour.
• With drawOnChanged, FlutterRiveRenderBox still advances every tick but only repaints when didChange is true or a redraw is forced (first frame, layout, painter swap, scheduleRepaint/fit/alignment, pointer, image decode, last advance before the ticker stops). The box becomes a repaint boundary.
• Opt-in because a gap in dirt tracking (cf. #14701, opacity 0) would show a stale frame; the default can flip later like iOS/web. Factory.rive isn't covered (texture cleared before advance).

Benchmark (Galaxy Z Flip6, profile, 60 Hz, at rest, 10 s windows)

Build time roughly halved and ~10 CPU points saved. GPU is unchanged because frames keep coming while the ticker runs (see the related issue).

Tests

New draw_optimization_test.dart 13/13 (fails without the gate); artboard_did_change_test.dart 1 pass / 2 skipped with the prebuilt library (no export; verified with llvm-nm on Android builds and on device); nearby existing suites 63/63 unchanged.

Reproduction steps / code

Any Rive animation that keeps advancing while holding still (e.g. a looping timeline with constant keys), shown with RiveWidget on Factory.flutter: DevTools shows a Rive repaint on every frame although Artboard::didChange() is false.

Rive Flutter package version

rive 0.14.11 (rive_native 0.1.11); patch based on rive_native 0.2.0-dev.3.

Flutter version

Flutter 3.47.3 (stable), Dart 3.13.3

Device

Samsung Galaxy Z Flip6 (SM-F741B)

OS version

Android 16

Additional context

Related: #664 (state machine never settles after the max-iterations cap).

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