Add Chart Widget

@@ -6,6 +6,7 @@
 - Fix PdfColors.shade()
 - Add dashed lines to Decoration Widgets
 - Add TableRow decoration
+- Add Chart Widget [Marco Papula]
 
 ## 1.6.2
 

@@ -54,3 +54,4 @@ part 'widgets/text_style.dart';
 part 'widgets/theme.dart';
 part 'widgets/widget.dart';
 part 'widgets/wrap.dart';
+part 'widgets/chart.dart';

+/*
+ * Copyright (C) 2017, David PHAM-VAN <dev.nfet.net@gmail.com>
+ *
+ * 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.
+ */
+
+// ignore_for_file: omit_local_variable_types
+
+part of widget;
+
+bool _isSortedAscending(List<double> list) {
+  double prev = list.first;
+  for (double elem in list) {
+    if (prev > elem) {
+      return false;
+    }
+    prev = elem;
+  }
+  return true;
+}
+
+class Chart extends Widget {
+  Chart({
+    @required this.grid,
+    @required this.data,
+    this.width = 500,
+    this.height = 250,
+    this.fit = BoxFit.contain,
+  });
+
+  final double width;
+  final double height;
+  final BoxFit fit;
+  final Grid grid;
+  final List<DataSet> data;
+  PdfRect gridBox;
+
+  @override
+  void layout(Context context, BoxConstraints constraints,
+      {bool parentUsesSize = false}) {
+    final double w = constraints.hasBoundedWidth
+        ? constraints.maxWidth
+        : constraints.constrainWidth(width.toDouble());
+    final double h = constraints.hasBoundedHeight
+        ? constraints.maxHeight
+        : constraints.constrainHeight(height.toDouble());
+
+    final FittedSizes sizes =
+        applyBoxFit(fit, PdfPoint(width, height), PdfPoint(w, h));
+
+    box = PdfRect.fromPoints(PdfPoint.zero, sizes.destination);
+    grid.layout(context, box);
+    for (DataSet dataSet in data) {
+      dataSet.layout(context, grid.gridBox);
+    }
+  }
+
+  @override
+  void paint(Context context) {
+    super.paint(context);
+
+    final Matrix4 mat = Matrix4.identity();
+    mat.translate(box.x, box.y);
+    context.canvas
+      ..saveContext()
+      ..setTransform(mat);
+
+    grid.paint(context, box);
+    for (DataSet dataSet in data) {
+      dataSet.paint(context, grid);
+    }
+    context.canvas.restoreContext();
+  }
+}
+
+abstract class Grid {
+  PdfRect gridBox;
+  double xOffset;
+  double xTotal;
+  double yOffset;
+  double yTotal;
+
+  void layout(Context context, PdfRect box);
+  void paint(Context context, PdfRect box);
+}
+
+class LinearGrid extends Grid {
+  LinearGrid({
+    @required this.xAxis,
+    @required this.yAxis,
+    this.xMargin = 10,
+    this.yMargin = 2,
+    this.textStyle,
+    this.lineWidth = 1,
+    this.color = PdfColors.black,
+    this.separatorLineWidth = 1,
+    this.separatorColor = PdfColors.grey,
+  })  : assert(_isSortedAscending(xAxis)),
+        assert(_isSortedAscending(yAxis));
+
+  final List<double> xAxis;
+  final List<double> yAxis;
+  final double xMargin;
+  final double yMargin;
+  final TextStyle textStyle;
+  final double lineWidth;
+  final PdfColor color;
+
+  TextStyle style;
+  PdfFont font;
+  PdfFontMetrics xAxisFontMetric;
+  PdfFontMetrics yAxisFontMetric;
+  double separatorLineWidth;
+  PdfColor separatorColor;
+
+  @override
+  void layout(Context context, PdfRect box) {
+    style = Theme.of(context).defaultTextStyle.merge(textStyle);
+    font = style.font.getFont(context);
+
+    xAxisFontMetric =
+        font.stringMetrics(xAxis.reduce(math.max).toStringAsFixed(1)) *
+            (style.fontSize);
+    yAxisFontMetric =
+        font.stringMetrics(yAxis.reduce(math.max).toStringAsFixed(1)) *
+            (style.fontSize);
+
+    gridBox = PdfRect.fromLTRB(
+        box.left + yAxisFontMetric.width + xMargin,
+        box.bottom + xAxisFontMetric.height + yMargin,
+        box.right - xAxisFontMetric.width / 2,
+        box.top - yAxisFontMetric.height / 2);
+
+    xOffset = xAxis.reduce(math.min);
+    yOffset = yAxis.reduce(math.min);
+    xTotal = xAxis.reduce(math.max) - xOffset;
+    yTotal = yAxis.reduce(math.max) - yOffset;
+  }
+
+  @override
+  void paint(Context context, PdfRect box) {
+    xAxis.asMap().forEach((int i, double x) {
+      context.canvas
+        ..setColor(style.color)
+        ..drawString(
+          style.font.getFont(context),
+          style.fontSize,
+          x.toStringAsFixed(1),
+          gridBox.left +
+              gridBox.width * i / (xAxis.length - 1) -
+              xAxisFontMetric.width / 2,
+          0,
+        );
+    });
+
+    for (double y in yAxis.where((double y) => y != yAxis.first)) {
+      final double textWidth =
+          (font.stringMetrics(y.toStringAsFixed(1)) * (style.fontSize)).width;
+      final double yPos = gridBox.bottom + gridBox.height * y / yAxis.last;
+      context.canvas
+        ..setColor(style.color)
+        ..drawString(
+          style.font.getFont(context),
+          style.fontSize,
+          y.toStringAsFixed(1),
+          xAxisFontMetric.width / 2 - textWidth / 2,
+          yPos - font.ascent,
+        );
+
+      context.canvas.drawLine(
+          gridBox.left,
+          yPos + font.descent + font.ascent - separatorLineWidth / 2,
+          gridBox.right,
+          yPos + font.descent + font.ascent - separatorLineWidth / 2);
+    }
+    context.canvas
+      ..setStrokeColor(separatorColor)
+      ..setLineWidth(separatorLineWidth)
+      ..strokePath();
+
+    context.canvas
+      ..setStrokeColor(color)
+      ..setLineWidth(lineWidth)
+      ..drawLine(gridBox.left, gridBox.bottom, gridBox.right, gridBox.bottom)
+      ..drawLine(gridBox.left, gridBox.bottom, gridBox.left, gridBox.top)
+      ..strokePath();
+  }
+}
+
+class ChartValue {
+  ChartValue(this.x, this.y);
+  final double x;
+  final double y;
+}
+
+abstract class DataSet {
+  void layout(Context context, PdfRect box);
+  void paint(Context context, Grid grid);
+}
+
+class LineDataSet extends DataSet {
+  LineDataSet({
+    @required this.data,
+    this.pointColor = PdfColors.green,
+    this.pointSize = 8,
+    this.lineColor = PdfColors.blue,
+    this.lineWidth = 2,
+    this.drawLine = true,
+    this.drawPoints = true,
+    this.lineStartingPoint,
+  }) : assert(drawLine || drawPoints);
+
+  final List<ChartValue> data;
+  final PdfColor pointColor;
+  final double pointSize;
+  final PdfColor lineColor;
+  final double lineWidth;
+  final bool drawLine;
+  final bool drawPoints;
+  final ChartValue lineStartingPoint;
+
+  double maxValue;
+
+  @override
+  void layout(Context context, PdfRect box) {}
+
+  @override
+  void paint(Context context, Grid grid) {
+    if (drawLine) {
+      ChartValue lastValue = lineStartingPoint;
+      for (ChartValue value in data) {
+        if (lastValue != null) {
+          context.canvas.drawLine(
+            grid.gridBox.left +
+                grid.gridBox.width * (lastValue.x - grid.xOffset) / grid.xTotal,
+            grid.gridBox.bottom +
+                grid.gridBox.height *
+                    (lastValue.y - grid.yOffset) /
+                    grid.yTotal,
+            grid.gridBox.left +
+                grid.gridBox.width * (value.x - grid.xOffset) / grid.xTotal,
+            grid.gridBox.bottom +
+                grid.gridBox.height * (value.y - grid.yOffset) / grid.yTotal,
+          );
+        }
+        lastValue = value;
+      }
+
+      context.canvas
+        ..setStrokeColor(lineColor)
+        ..setLineWidth(lineWidth)
+        ..setLineCap(PdfLineCap.joinRound)
+        ..setLineJoin(PdfLineCap.joinRound)
+        ..strokePath();
+    }
+
+    if (drawPoints) {
+      for (ChartValue value in data) {
+        context.canvas
+          ..setColor(pointColor)
+          ..drawEllipse(
+              grid.gridBox.left +
+                  grid.gridBox.width * (value.x - grid.xOffset) / grid.xTotal,
+              grid.gridBox.bottom +
+                  grid.gridBox.height * (value.y - grid.yOffset) / grid.yTotal,
+              pointSize,
+              pointSize)
+          ..fillPath();
+      }
+    }
+  }
+}

+/*
+ * Copyright (C) 2017, David PHAM-VAN <dev.nfet.net@gmail.com>
+ *
+ * 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.
+ */
+
+// ignore_for_file: omit_local_variable_types
+
+import 'dart:io';
+
+import 'package:test/test.dart';
+import 'package:pdf/pdf.dart';
+import 'package:pdf/widgets.dart';
+
+Document pdf;
+
+void main() {
+  setUpAll(() {
+    Document.debug = true;
+    pdf = Document();
+  });
+
+  group('LineChart test', () {
+    test('Default LineChart', () {
+      pdf.addPage(Page(
+        build: (Context context) => Chart(
+          grid: LinearGrid(
+            xAxis: <double>[0, 1, 2, 3, 4, 5, 6],
+            yAxis: <double>[0, 3, 6, 9],
+          ),
+          data: <DataSet>[
+            LineDataSet(
+              data: <ChartValue>[
+                ChartValue(1, 1),
+                ChartValue(2, 3),
+                ChartValue(3, 7),
+              ],
+            ),
+          ],
+        ),
+      ));
+    });
+
+    test('Default LineChart without lines connecting points', () {
+      pdf.addPage(Page(
+        build: (Context context) => Chart(
+          grid: LinearGrid(
+            xAxis: <double>[0, 1, 2, 3, 4, 5, 6],
+            yAxis: <double>[0, 3, 6, 9],
+          ),
+          data: <DataSet>[
+            LineDataSet(
+              data: <ChartValue>[
+                ChartValue(1, 1),
+                ChartValue(2, 3),
+                ChartValue(3, 7),
+              ],
+              drawLine: false,
+            ),
+          ],
+        ),
+      ));
+    });
+
+    test('Default ScatterChart without dots', () {
+      pdf.addPage(Page(
+        build: (Context context) => Chart(
+          grid: LinearGrid(
+            xAxis: <double>[0, 1, 2, 3, 4, 5, 6],
+            yAxis: <double>[0, 3, 6, 9],
+          ),
+          data: <DataSet>[
+            LineDataSet(
+              data: <ChartValue>[
+                ChartValue(1, 1),
+                ChartValue(2, 3),
+                ChartValue(3, 7),
+              ],
+              drawPoints: false,
+            ),
+          ],
+        ),
+      ));
+    });
+
+    test('ScatterChart with custom points and lines', () {
+      pdf.addPage(Page(
+        build: (Context context) => Chart(
+          grid: LinearGrid(
+            xAxis: <double>[0, 1, 2, 3, 4, 5, 6],
+            yAxis: <double>[0, 3, 6, 9],
+          ),
+          data: <DataSet>[
+            LineDataSet(
+              data: <ChartValue>[
+                ChartValue(1, 1),
+                ChartValue(2, 3),
+                ChartValue(3, 7),
+              ],
+              drawLine: false,
+              pointColor: PdfColors.red,
+              pointSize: 4,
+              lineColor: PdfColors.purple,
+              lineWidth: 4,
+            ),
+          ],
+        ),
+      ));
+    });
+
+    test('ScatterChart with custom size', () {
+      pdf.addPage(Page(
+        build: (Context context) => Chart(
+          width: 200,
+          height: 100,
+          grid: LinearGrid(
+            xAxis: <double>[0, 1, 2, 3, 4, 5, 6],
+            yAxis: <double>[0, 3, 6, 9],
+          ),
+          data: <DataSet>[
+            LineDataSet(
+              data: <ChartValue>[
+                ChartValue(1, 1),
+                ChartValue(2, 3),
+                ChartValue(3, 7),
+              ],
+            ),
+          ],
+        ),
+      ));
+    });
+  });
+
+  tearDownAll(() {
+    final File file = File('widgets-chart.pdf');
+    file.writeAsBytesSync(pdf.save());
+  });
+}