Examples - Add Variable Timestep Example

lib/src/03-VariableTimestep.dart

@@ -0,0 +1,48 @@
+//void main() {
+//  double lastTime = performance.now();
+//  while(true) {
+//    double currentTime = performance.now();
+//    double delta = currentTime - lastTime;
+//
+//    update(delta);
+//
+//    lastTime = currentTime;
+//  }
+//}
+
+import 'dart:html';
+import 'package:browserloop/game/Game.dart';
+import 'package:browserloop/game/LoopExample.dart';
+
+/// The Variable Timestep Loop.
+///
+/// Perhaps one of the most widely used loops
+/// in games for many years. Many game frameworks
+/// make use of a loop similar to this.
+class VariableTimestep implements LoopExample {
+  Game game;
+  num id;
+  Stopwatch elapsed = new Stopwatch();
+
+  VariableTimestep(Game this.game) {
+    elapsed.start();
+    window.requestAnimationFrame(eventloop);
+  }
+
+  void eventloop(num time) {
+    int dt = elapsed.elapsedMilliseconds;
+    game.update(dt);
+    game.draw();
+    elapsed.reset();
+
+    id = window.requestAnimationFrame(eventloop);
+  }
+
+  void stop() {
+    window.cancelAnimationFrame(id);
+  }
+
+  void start() {
+    window.requestAnimationFrame(eventloop);
+  }
+}