add FlareProgressController

Author: lukepighetti

flare_flutter/lib/flare_progress_controller.dart

@@ -0,0 +1,43 @@
+import 'package:flare_dart/math/mat2d.dart';
+
+import 'flare.dart';
+import 'flare_controller.dart';
+
+/// A naiive controller that allows you to scrub through a single animation.
+/// Useful for wiring up progress bars or scroll based animations.
+class FlareProgressController extends FlareController {
+  FlareProgressController(this.animation);
+
+  final String animation;
+
+  FlutterActorArtboard _artboard;
+  ActorAnimation _animation;
+
+  @override
+  bool advance(FlutterActorArtboard artboard, double elapsed) {
+    return false;
+  }
+
+  @override
+  void initialize(FlutterActorArtboard artboard) {
+    _artboard = artboard;
+    if (_artboard != null) {
+      _animation = artboard.getAnimation(animation);
+
+      if (_animation != null) {
+        _animation.apply(0.0, _artboard, 1.0);
+      }
+    }
+  }
+
+  /// Updates the animation progress and triggers a render
+  void update(double t) {
+    if (_animation != null) {
+      final time = _animation.duration * t;
+      _animation.apply(time, _artboard, 1.0);
+    }
+  }
+
+  @override
+  void setViewTransform(Mat2D viewTransform) {}
+}