First pass on action animations for sprites

sky/sdk/example/game/lib/action.dart

Index: sky/sdk/example/game/lib/action.dart
diff --git a/sky/sdk/example/game/lib/action.dart b/sky/sdk/example/game/lib/action.dart
new file mode 100644
index 0000000000000000000000000000000000000000..e2d9cf33bbd88f63b0bb4e02a679680f4a3ca424
--- /dev/null
+++ b/sky/sdk/example/game/lib/action.dart
@@ -0,0 +1,155 @@
+part of sprites;
+
+typedef void PointSetter(Point point);
+
+abstract class Action {
+  bool _finished = false;
+
+  void step(double dt);
+  void update(double t);
+}
+
+abstract class ActionInterval extends Action {
+  double _duration;
+
+  bool _firstTick = true;
+  double _elapsed = 0.0;
+
+  double get duration => _duration;
+
+  ActionInterval([this._duration = 0.0]);
+
+  void step(double dt) {
+    if (_firstTick) {
+      _firstTick = false;
+    } else {
+      _elapsed += dt;
+    }
+
+    double t;
+    if (this._duration == 0.0) {
+      t = 1.0;
+    } else {
+      t = _clamp(_elapsed / _duration, 0.0, 1.0);
+    }
+
+    update(t);
+
+    if (t >= 1.0) _finished = true;
+  }
+}
+
+class ActionRepeat extends ActionInterval {
+  final int numRepeats;
+  final ActionInterval action;
+
+  ActionRepeat(this.action, this.numRepeats) {
+    _duration = action.duration * numRepeats;
+  }
+
+  void update(double t) {
+    action.update((t * numRepeats.toDouble()) % numRepeats.toDouble());
+  }
+}
+
+// TODO: Implement
+class ActionSequence extends ActionInterval {
+  final List<ActionInterval> actions;
+
+  ActionSequence(this.actions) {
+    for (Action action in actions) {
+      _duration += action._duration;
+    }
+  }
+}
+
+class ActionRepeatForever extends Action {
+  final ActionInterval action;
+  double _elapsedInAction = 0.0;
+
+  ActionRepeatForever(this.action);
+
+  step(double dt) {
+    _elapsedInAction += dt;
+    while (_elapsedInAction > action.duration) {
+      _elapsedInAction -= action.duration;
+    }
+    _elapsedInAction = Math.max(_elapsedInAction, 0.0);
+
+    double t;
+    if (action._duration == 0.0) {
+      t = 1.0;
+    } else {
+      t = _clamp(_elapsedInAction / action._duration, 0.0, 1.0);
+    }
+
+    action.update(t);
+  }
+}
+
+class ActionTween extends ActionInterval {
+  final Function setter;
+  final startVal;
+  final endVal;
+
+  var _delta;
+
+  ActionTween(this.setter, this.startVal, this.endVal, double duration) : super(duration) {
+    _computeDelta();
+  }
+
+  void _computeDelta() {
+    if (startVal is Point) {
+      double xStart = startVal.x;
+      double yStart = startVal.y;
+      double xEnd = endVal.x;
+      double yEnd = endVal.y;
+      _delta = new Point(xEnd - xStart, yEnd - yStart);
+    } else if (startVal is double) {
+      _delta = endVal - startVal;
+    } else {
+      assert(false);
+    }
+  }
+
+  void update(double t) {
+    var newVal;
+
+    if (startVal is Point) {
+      double xStart = startVal.x;
+      double yStart = startVal.y;
+      double xDelta = _delta.x;
+      double yDelta = _delta.y;
+
+      newVal = new Point(xStart + xDelta * t, yStart + yDelta * t);
+    } else if (startVal is double) {
+      newVal = startVal + _delta * t;
+    } else {
+      assert(false);
+    }
+
+    setter(newVal);
+  }
+}
+
+class ActionController {
+
+  List<Action> _actions = [];
+
+  ActionController();
+
+  void run(Action action) {
+    _actions.add(action);
+  }
+
+  void step(double dt) {
+    for (int i = _actions.length - 1; i >= 0; i--) {
+      Action action = _actions[i];
+      action.step(dt);
+
+      if (action._finished) {

[kulakowski, 2015/07/01 22:18:43]

How many actions can be pending? If it's a bunch, maybe calling

actions.removeWhere((a) => a._finished);

is more efficient (the API docs are unclear about the exact allocation strategy
of List).

+        _actions.removeAt(i);
+      }
+    }
+  }
+}