Add flutter_web samples (#75)

web/charts/example/lib/axes/flipped_vertical_axis.dart

@@ -0,0 +1,114 @@
+// 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.
+
+/// Bar chart example
+// EXCLUDE_FROM_GALLERY_DOCS_START
+import 'dart:math';
+// EXCLUDE_FROM_GALLERY_DOCS_END
+import 'package:flutter_web/material.dart';
+import 'package:charts_flutter/flutter.dart' as charts;
+
+/// Example of flipping the vertical measure axis direction so that larger
+/// values render downward instead of the usual rendering up.
+///
+/// flipVerticalAxis, when set, flips the vertical axis from its default
+/// direction.
+///
+/// Note: primary and secondary may flip left and right positioning when
+/// RTL.flipAxisLocations is set.
+class FlippedVerticalAxis extends StatelessWidget {
+  final List<charts.Series> seriesList;
+  final bool animate;
+
+  FlippedVerticalAxis(this.seriesList, {this.animate});
+
+  factory FlippedVerticalAxis.withSampleData() {
+    return new FlippedVerticalAxis(
+      _createSampleData(),
+      // Disable animations for image tests.
+      animate: false,
+    );
+  }
+
+  // EXCLUDE_FROM_GALLERY_DOCS_START
+  // This section is excluded from being copied to the gallery.
+  // It is used for creating random series data to demonstrate animation in
+  // the example app only.
+  factory FlippedVerticalAxis.withRandomData() {
+    return new FlippedVerticalAxis(_createRandomData());
+  }
+
+  /// Create random data.
+  static List<charts.Series<RunnerRank, String>> _createRandomData() {
+    final random = new Random();
+
+    const runners = ['Smith', 'Jones', 'Brown', 'Doe'];
+
+    // Randomly assign runners, but leave the order of the places.
+    final raceData = [
+      new RunnerRank(runners.removeAt(random.nextInt(runners.length)), 1),
+      new RunnerRank(runners.removeAt(random.nextInt(runners.length)), 2),
+      new RunnerRank(runners.removeAt(random.nextInt(runners.length)), 3),
+      new RunnerRank(runners.removeAt(random.nextInt(runners.length)), 4),
+    ];
+
+    return [
+      new charts.Series<RunnerRank, String>(
+        id: 'Race Results',
+        domainFn: (RunnerRank row, _) => row.name,
+        measureFn: (RunnerRank row, _) => row.place,
+        data: raceData,
+      ),
+    ];
+  }
+  // EXCLUDE_FROM_GALLERY_DOCS_END
+
+  // Known Issue, the bar chart cannot render negative direction bars at this
+  // time so the result is an empty chart.
+  // TODO: Remove this comment
+  @override
+  Widget build(BuildContext context) {
+    return new charts.BarChart(
+      seriesList,
+      animate: animate,
+      flipVerticalAxis: true,
+    );
+  }
+
+  /// Create series list with multiple series
+  static List<charts.Series<RunnerRank, String>> _createSampleData() {
+    final raceData = [
+      new RunnerRank('Smith', 1),
+      new RunnerRank('Jones', 2),
+      new RunnerRank('Brown', 3),
+      new RunnerRank('Doe', 4),
+    ];
+
+    return [
+      new charts.Series<RunnerRank, String>(
+          id: 'Race Results',
+          domainFn: (RunnerRank row, _) => row.name,
+          measureFn: (RunnerRank row, _) => row.place,
+          data: raceData),
+    ];
+  }
+}
+
+/// Datum/Row for the chart.
+class RunnerRank {
+  final String name;
+  final int place;
+  RunnerRank(this.name, this.place);
+}