Add a simple inksplash example

We'll eventually turn this into a full fn2 component, but for now it's just an
example.

To make this work, I created a schedule.dart as a start to implementing
scheduler.md. For now, I've kept the API similar to the web platform so that
the old world can continue use it backed by sky.window.requestAnimationFrame.

R=eseidel@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1145973009

examples/raw/ink_well.dart

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:sky' as sky;
+import 'package:sky/framework/app.dart';
+import 'package:sky/framework/rendering/render_box.dart';
+import 'package:sky/framework/rendering/render_node.dart';
+import 'package:sky/framework/animation/animated_value.dart';
+import 'package:sky/framework/animation/curves.dart';
+
+const double _kInitialSize = 0.0;
+const double _kTargetSize = 100.0;
+const double _kSplashDuration = 500.0;
+const int _kInitialOpacity = 0x80;
+
+class InkSplash {
+  final InkWell inkWell;
+  final sky.Paint _paint = new sky.Paint();
+  final sky.Point position;
+  AnimatedValue radius;
+
+  InkSplash({ this.position, this.inkWell }) {
+    radius = new AnimatedValue(_kInitialSize, onChange: _handleRadiusChange);
+    radius.animateTo(_kTargetSize, _kSplashDuration, curve: easeOut);
+  }
+
+  void _handleRadiusChange() {
+    if (radius.value == _kTargetSize)
+      inkWell._splashes.remove(this);
+    inkWell.markNeedsPaint();
+  }
+
+  void paint(RenderNodeDisplayList canvas) {
+    int opacity = (_kInitialOpacity * (1.0 - (radius.value / _kTargetSize))).floor();
+    _paint.color = opacity << 24;
+    canvas.drawCircle(position.x, position.y, radius.value, _paint);
+  }
+}
+
+class InkWell extends RenderBox {
+  final List<InkSplash> _splashes = new List<InkSplash>();
+
+  void handlePointer(sky.PointerEvent event) {
+    switch (event.type) {
+      case 'pointerdown':
+        _splashes.add(new InkSplash(position: new sky.Point(event.x, event.y),
+                                    inkWell: this));
+        break;
+    }
+    markNeedsPaint();
+  }
+
+  void performLayout() {
+    size = constraints.constrain(new sky.Size.infinite());
+  }
+
+  void paint(RenderNodeDisplayList canvas) {
+    canvas.drawRect(new sky.Rect.fromLTRB(0.0, 0.0, size.width, size.height),
+                    new sky.Paint()..color = 0xFFCCCCCC);
+    for (InkSplash splash in _splashes)
+      splash.paint(canvas);
+  }
+}
+
+AppView app;
+
+void main() {
+  app = new AppView(new InkWell());
+}

examples/raw/touch_demo.dart

@@ -61,6 +61,10 @@ class RenderTouchDemo extends RenderBox {
     markNeedsPaint();
   }
 
+  void performLayout() {
+    size = constraints.constrain(new Size.infinite());
+  }
+
   void paint(RenderNodeDisplayList canvas) {
     dots.forEach((_, Dot dot) {
       dot.paint(canvas);

sdk/BUILD.gn

@@ -100,6 +100,7 @@ dart_pkg("sdk") {
     "lib/framework/rendering/render_flex.dart",
     "lib/framework/rendering/render_node.dart",
     "lib/framework/rendering/render_paragraph.dart",
+    "lib/framework/scheduler.dart",
     "lib/framework/shell.dart",
     "lib/framework/theme/colors.dart",
     "lib/framework/theme/shadows.dart",

sdk/lib/framework/animation/generators.dart

@@ -2,10 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import '../scheduler.dart' as scheduler;
 import 'curves.dart';
 import 'dart:async';
 import 'dart:math' as math;
-import 'dart:sky' as sky;
 import 'mechanics.dart';
 
 abstract class Generator {
@@ -34,7 +34,7 @@ class FrameGenerator extends Generator {
       return;
     }
     if (_animationId != 0) {
-      sky.window.cancelAnimationFrame(_animationId);
+      scheduler.cancelAnimationFrame(_animationId);
     }
     _animationId = 0;
     _cancelled = true;
@@ -45,7 +45,7 @@ class FrameGenerator extends Generator {
 
   void _scheduleTick() {
     assert(_animationId == 0);
-    _animationId = sky.window.requestAnimationFrame(_tick);
+    _animationId = scheduler.requestAnimationFrame(_tick);
   }
 
   void _tick(double timeStamp) {

sdk/lib/framework/app.dart

@@ -5,18 +5,20 @@
 import 'dart:sky' as sky;
 import 'rendering/render_box.dart';
 import 'rendering/render_node.dart';
+import 'scheduler.dart' as scheduler;
 
 class AppView {
 
   AppView(RenderBox root) {
     sky.view.setEventCallback(_handleEvent);
-    sky.view.setBeginFrameCallback(_beginFrame);
+    scheduler.init();
+    scheduler.addPersistentFrameCallback(_beginFrame);
 
     _renderView = new RenderView(child: root);
     _renderView.attach();
     _renderView.layout(new ViewConstraints(width: sky.view.width, height: sky.view.height));
 
-    sky.view.scheduleFrame();
+    scheduler.ensureVisualUpdate();
   }
 
   RenderView _renderView;

sdk/lib/framework/rendering/render_node.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import '../node.dart';
+import '../scheduler.dart' as scheduler;
 import 'dart:math' as math;
 import 'dart:sky' as sky;
 
@@ -173,10 +174,7 @@ abstract class RenderNode extends AbstractNode {
   static bool debugDoingPaint = false;
   void markNeedsPaint() {
     assert(!debugDoingPaint);
-    // TODO(abarth): It's very redundant to call this for every node in the
-    // render tree during layout. We should instead compute a summary bit and
-    // call it once at the end of layout.
-    sky.view.scheduleFrame();
+    scheduler.ensureVisualUpdate();
   }
   void paint(RenderNodeDisplayList canvas) { }
 

sdk/lib/framework/scheduler.dart

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:async';
+import 'dart:sky' as sky;
+
+typedef void Callback(double timeStamp);
+
+bool _haveScheduledVisualUpdate = false;
+int _nextCallbackId = 1;
+
+final List<Callback> _persistentCallbacks = new List<Callback>();
+Map<int, Callback> _transientCallbacks = new Map<int, Callback>();
+
+void _beginFrame(double timeStamp) {
+  _haveScheduledVisualUpdate = false;
+
+  Map<int, Callback> callbacks = _transientCallbacks;
+  _transientCallbacks = new Map<int, Callback>();
+
+  callbacks.forEach((id, callback) {
+    callback(timeStamp);
+  });
+
+  for (Callback callback in _persistentCallbacks)
+    callback(timeStamp);
+}
+
+void init() {
+  assert(sky.window == null);
+  sky.view.setBeginFrameCallback(_beginFrame);
+}
+
+void addPersistentFrameCallback(Callback callback) {
+  assert(sky.window == null);
+  _persistentCallbacks.add(callback);
+}
+
+int requestAnimationFrame(Callback callback) {
+  if (sky.window != null)
+    return sky.window.requestAnimationFrame(callback);
+  int id = _nextCallbackId++;
+  _transientCallbacks[id] = callback;
+  ensureVisualUpdate();
+  return id;
+}
+
+void cancelAnimationFrame(int id) {
+  if (sky.window != null)
+    return sky.window.cancelAnimationFrame(id);
+  _transientCallbacks.remove(id);
+}
+
+void ensureVisualUpdate() {
+  assert(sky.window == null);
+  if (_haveScheduledVisualUpdate)
+    return;
+  sky.view.scheduleFrame();
+  _haveScheduledVisualUpdate = true;
+}