fix: always advance

Fixes #408 and #409

I left some notes in the code for future consideration, @luigi-rosso. This is the least intrusive change that will not break golden tests (for us and users).

Diffs=
fd6aa55ed fix: always advance (#7615)
49cabe3cb update data bind mode to flags (#7612)
6c5c79b75 Only set Core Audio session category for iOS targets (#7624)
8e1be1223 Run tests, bench, gms, & goldens on a physical Pixel 8 on CI (#7618)
238bf2fe1 Set audio to mix on for iOS (simulator) and Catalyst (#7555)
ca56d7565 Vulkan! (#7553)
63b6a13d3 Use "python3" in make_viewer_skia.sh (instead of "python") (#7597)
8a67331a4 Fix build on web. (#7613)
44fae6bfe explicit linux arch (#7606)
2a1db3835 handle linux warnings (#7598)
c5eb69645 add pic (#7589)
3bf0df5c0 Fixing windows build with rive_native. (#7575)

Co-authored-by: Gordon <pggordonhayes@gmail.com>

.rive_head

@@ -1 +1 @@
-a0a6c0d3bd385f32dd51e1fbcb75306332b9d1cc
+fd6aa55ed53ab88fcc9ece52bc6cc7bb2680f5de

CHANGELOG.md

@@ -1,19 +1,28 @@
+## Upcoming
+
+- Fix [408](https://github.com/rive-app/rive-flutter/issues/408) and [409](https://github.com/rive-app/rive-flutter/issues/409), Rive never reaching a settled state when the widget is not visible (paint method not called).
+
 ## 0.13.9
+
 - Preperation for data binding ([databinding](https://github.com/rive-app/rive-flutter/commit/6ceb7a544e7124d303259f7d032641e5b38f7fc1), [data binding data context](https://github.com/rive-app/rive-flutter/commit/6d002300a6f0fd19f6dacac58a499ccc903a214d), [databinding add boolean](https://github.com/rive-app/rive-flutter/commit/90b8c81f0e496502b70db4d550341f5acabbbea6)).
 - Layout fixes and improvements ([animations for layouts](https://github.com/rive-app/rive-flutter/commit/8068e48eb2faa2a13eab1ba858b4e0737cf0265b), [layout UX fixes](https://github.com/rive-app/rive-flutter/commit/21bd3765ddc3ef8c3b1f0199f75eae21434cf52b)).
 - Android example project [fix](https://github.com/rive-app/rive-flutter/commit/9951f912df4c6f0574f57d5a152cd36e6ad2d7e0).
 
 ## 0.13.8
+
 - Add `key` property to `Rive` widget.
 - Nested linear animations report events up to parent artboards. Previously, only nested state machines could report events so that listeners in parent artboards could listen for them.
 
 ## 0.13.7
+
 - Add `getComponentWhereOrNull` on `Artboard`, to find a component that matches the given predicate. This can be used instead of `forEachComponent` as it allows exiting early.
 
 ## 0.13.6
+
 - Add `getBoolInput(name, path)`, `getTriggerInput(name, path)`, and `getNumberInput(name, path` on `Artboard` to set nested inputs (inputs on nested artboards), see [the documentation](https://rive.app/community/doc/state-machines/docxeznG7iiK#nested-inputs).
 
 ## 0.13.5
+
 - Migrates to `dart:js_interop` and `package:web` APIs.
 - DEPRECATED: `RiveFile.initializeText` - use `RiveFile.initialize` instead. This now initializes the Rive audio, text, and layout engine. Call `await RiveFile.initialize()` before doing `RiveFile.import`. `RiveFile.asset`, `RiveFile.network`, and `RiveFile.file` will call initialize automatically if it has not been initialized. Alternatively, you can also call `unawaited(RiveFile.initialize());` in the `main` method on app start to make the first graphic load faster.
 

lib/src/rive_render_box.dart

@@ -89,6 +89,8 @@ abstract class RiveRenderBox extends RenderBox {
     }
   }
 
+  bool _paintedLastFrame = false;
+
   @override
   bool get sizedByParent => !useArtboardSize;
 
@@ -257,8 +259,33 @@ abstract class RiveRenderBox extends RenderBox {
   }
 
   void _frameCallback(Duration duration) {
+    // Under certain conditions Flutter will not call paint (for optimization).
+    // If the animation did not paint in the last frame, we force
+    // advance so that the animation can reach a settled state.
+
+    // TODO: Ideally "advance" should only happen inside_`_frameCallback`
+    // and not inside `paint`. But to support backwards compatibility we
+    // will continue to advance in `paint` (golden tests), and just introduce
+    // this as a backup to resolve:
+    // - https://github.com/rive-app/rive-flutter/issues/409
+    // - https://github.com/rive-app/rive-flutter/issues/408
+    //
+    // In the next version of the runtime that uses rive_native we can rework
+    // this logic.
+    //
+    // TODO: We also need to consider standard default behaviour for what
+    // Rive should do when not visible on the screen
+    // - Advance and not draw
+    // - Draw and advance
+    // - Neither advance nor draw
+    // - (Optional enum for users to choose)
+    if (!_paintedLastFrame) {
+      _advanceFrame();
+    }
+
     _calculateElapsedSeconds(duration);
 
+    _paintedLastFrame = false;
     markNeedsPaint();
   }
 
@@ -349,13 +376,18 @@ abstract class RiveRenderBox extends RenderBox {
     return transform;
   }
 
-  @protected
-  @override
-  void paint(PaintingContext context, Offset offset) {
+  void _advanceFrame() {
     if (!advance(_elapsedSeconds)) {
       _stopTicker();
     }
     _elapsedSeconds = 0;
+  }
+
+  @protected
+  @override
+  void paint(PaintingContext context, Offset offset) {
+    _paintedLastFrame = true;
+    _advanceFrame();
 
     if (customPaint(context, offset)) {
       return;