Add flutter_web samples (#75)

web/charts/flutter/lib/src/chart_gesture_detector.dart

@@ -0,0 +1,136 @@
+// Copyright 2018 the Charts project authors. Please see the AUTHORS file
+// for details.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import 'dart:async' show Timer;
+import 'dart:math' show Point;
+import 'package:flutter_web/material.dart'
+    show
+        BuildContext,
+        GestureDetector,
+        ScaleEndDetails,
+        ScaleStartDetails,
+        ScaleUpdateDetails,
+        TapDownDetails,
+        TapUpDetails;
+
+import 'behaviors/chart_behavior.dart' show GestureType;
+import 'chart_container.dart' show ChartContainer, ChartContainerRenderObject;
+import 'util.dart' show getChartContainerRenderObject;
+
+// From https://docs.flutter.io/flutter/gestures/kLongPressTimeout-constant.html
+const Duration _kLongPressTimeout = const Duration(milliseconds: 500);
+
+class ChartGestureDetector {
+  bool _listeningForLongPress;
+
+  bool _isDragging = false;
+
+  Timer _longPressTimer;
+  Point<double> _lastTapPoint;
+  double _lastScale;
+
+  _ContainerResolver _containerResolver;
+
+  makeWidget(BuildContext context, ChartContainer chartContainer,
+      Set<GestureType> desiredGestures) {
+    _containerResolver =
+        () => getChartContainerRenderObject(context.findRenderObject());
+
+    final wantTapDown = desiredGestures.isNotEmpty;
+    final wantTap = desiredGestures.contains(GestureType.onTap);
+    final wantDrag = desiredGestures.contains(GestureType.onDrag);
+
+    // LongPress is special, we'd like to be able to trigger long press before
+    // Drag/Press to trigger tooltips then explore with them. This means we
+    // can't rely on gesture detection since it will block out the scale
+    // gestures.
+    _listeningForLongPress = desiredGestures.contains(GestureType.onLongPress);
+
+    return new GestureDetector(
+      child: chartContainer,
+      onTapDown: wantTapDown ? onTapDown : null,
+      onTapUp: wantTap ? onTapUp : null,
+      onScaleStart: wantDrag ? onScaleStart : null,
+      onScaleUpdate: wantDrag ? onScaleUpdate : null,
+      onScaleEnd: wantDrag ? onScaleEnd : null,
+    );
+  }
+
+  void onTapDown(TapDownDetails d) {
+    final container = _containerResolver();
+    final localPosition = container.globalToLocal(d.globalPosition);
+    _lastTapPoint = new Point(localPosition.dx, localPosition.dy);
+    container.gestureProxy.onTapTest(_lastTapPoint);
+
+    // Kick off a timer to see if this is a LongPress.
+    if (_listeningForLongPress) {
+      _longPressTimer = new Timer(_kLongPressTimeout, () {
+        onLongPress();
+        _longPressTimer = null;
+      });
+    }
+  }
+
+  void onTapUp(TapUpDetails d) {
+    _longPressTimer?.cancel();
+
+    final container = _containerResolver();
+    final localPosition = container.globalToLocal(d.globalPosition);
+    _lastTapPoint = new Point(localPosition.dx, localPosition.dy);
+    container.gestureProxy.onTap(_lastTapPoint);
+  }
+
+  void onLongPress() {
+    final container = _containerResolver();
+    container.gestureProxy.onLongPress(_lastTapPoint);
+  }
+
+  void onScaleStart(ScaleStartDetails d) {
+    _longPressTimer?.cancel();
+
+    final container = _containerResolver();
+    final localPosition = container.globalToLocal(d.focalPoint);
+    _lastTapPoint = new Point(localPosition.dx, localPosition.dy);
+
+    _isDragging = container.gestureProxy.onDragStart(_lastTapPoint);
+  }
+
+  void onScaleUpdate(ScaleUpdateDetails d) {
+    if (!_isDragging) {
+      return;
+    }
+
+    final container = _containerResolver();
+    final localPosition = container.globalToLocal(d.focalPoint);
+    _lastTapPoint = new Point(localPosition.dx, localPosition.dy);
+    _lastScale = d.scale;
+
+    container.gestureProxy.onDragUpdate(_lastTapPoint, d.scale);
+  }
+
+  void onScaleEnd(ScaleEndDetails d) {
+    if (!_isDragging) {
+      return;
+    }
+
+    final container = _containerResolver();
+
+    container.gestureProxy
+        .onDragEnd(_lastTapPoint, _lastScale, d.velocity.pixelsPerSecond.dx);
+  }
+}
+
+// Exposed for testing.
+typedef ChartContainerRenderObject _ContainerResolver();