Add Partitions Widget

@@ -12,6 +12,7 @@
 - Add Opacity Widget
 - Fix Text height with TrueType fonts
 - Convert Flex to a SpanningWidget
+- Add Partitions Widget
 
 ## 1.4.1
 

@@ -41,6 +41,7 @@ part 'widgets/image.dart';
 part 'widgets/multi_page.dart';
 part 'widgets/page.dart';
 part 'widgets/page_theme.dart';
+part 'widgets/partitions.dart';
 part 'widgets/placeholders.dart';
 part 'widgets/progress.dart';
 part 'widgets/qrcode.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;
+
+class Partition implements SpanningWidget {
+  Partition({
+    @required this.child,
+    this.width,
+    int flex = 1,
+  })  : flex = width == null ? flex : 0,
+        assert(flex != null),
+        assert(child != null);
+
+  final double width;
+
+  final int flex;
+
+  final SpanningWidget child;
+
+  @override
+  PdfRect get box => child.box;
+
+  @override
+  set box(PdfRect value) => child.box = value;
+
+  @override
+  bool get canSpan => child.canSpan;
+
+  @override
+  void debugPaint(Context context) {
+    child.debugPaint(context);
+  }
+
+  @override
+  void layout(Context context, BoxConstraints constraints,
+      {bool parentUsesSize = false}) {
+    child.layout(context, constraints, parentUsesSize: parentUsesSize);
+  }
+
+  @override
+  void paint(Context context) {
+    child.paint(context);
+  }
+
+  @override
+  void restoreContext(WidgetContext context) {
+    child.restoreContext(context);
+  }
+
+  @override
+  WidgetContext saveContext() {
+    return child.saveContext();
+  }
+
+  @override
+  bool get hasMoreWidgets => child.hasMoreWidgets;
+}
+
+class _PartitionsContext extends WidgetContext {
+  _PartitionsContext(int count) : partitionContext = List<WidgetContext>(count);
+
+  final List<WidgetContext> partitionContext;
+
+  @override
+  void apply(WidgetContext other) {
+    if (other is _PartitionsContext) {
+      for (int index = 0; index < partitionContext.length; index++) {
+        partitionContext[index]?.apply(other.partitionContext[index]);
+      }
+    }
+  }
+
+  @override
+  WidgetContext clone() {
+    final _PartitionsContext context =
+        _PartitionsContext(partitionContext.length);
+    for (int index = 0; index < partitionContext.length; index++) {
+      context.partitionContext[index] = partitionContext[index].clone();
+    }
+
+    return context;
+  }
+}
+
+class Partitions extends Widget implements SpanningWidget {
+  Partitions({
+    this.children,
+    this.mainAxisSize = MainAxisSize.max,
+  })  : _context = _PartitionsContext(children.length),
+        super();
+
+  final List<Partition> children;
+
+  final _PartitionsContext _context;
+
+  final MainAxisSize mainAxisSize;
+
+  @override
+  bool get canSpan => children.any((Partition part) => part.canSpan);
+
+  @override
+  bool get hasMoreWidgets =>
+      !children.any((Partition part) => !part.hasMoreWidgets);
+
+  @override
+  void layout(Context context, BoxConstraints constraints,
+      {bool parentUsesSize = false}) {
+    assert(constraints != null);
+
+    // Determine used flex factor, size inflexible items, calculate free space.
+    final double maxMainSize = constraints.maxWidth;
+    final bool canFlex = maxMainSize < double.infinity;
+    double allocatedSize = 0; // Sum of the sizes of the non-flexible children.
+    int totalFlex = 0;
+    final List<double> widths = List<double>.filled(children.length, 0);
+
+    // Calculate fixed width columns
+    int index = 0;
+    for (Partition child in children) {
+      if (child.flex > 0) {
+        assert(() {
+          if (!canFlex) {
+            throw Exception(
+                'Partition children have non-zero flex but incoming width constraints are unbounded.');
+          } else {
+            return true;
+          }
+        }());
+        totalFlex += child.flex;
+      } else {
+        allocatedSize += child.width;
+        widths[index] = child.width;
+      }
+      index++;
+    }
+
+    // Distribute free space to flexible children, and determine baseline.
+    if (totalFlex > 0 && canFlex) {
+      final double freeSpace =
+          math.max(0, (canFlex ? maxMainSize : 0.0) - allocatedSize);
+      final double spacePerFlex = freeSpace / totalFlex;
+
+      index = 0;
+      for (Partition child in children) {
+        if (child.flex > 0) {
+          final double childExtent = spacePerFlex * child.flex;
+          allocatedSize += childExtent;
+          widths[index] = childExtent;
+        }
+        index++;
+      }
+    }
+
+    // Layout the columns and compute the total height
+    double totalHeight = 0;
+    index = 0;
+    for (Partition child in children) {
+      if (widths[index] > 0) {
+        final BoxConstraints innerConstraints = BoxConstraints(
+            minWidth: widths[index],
+            maxWidth: widths[index],
+            maxHeight: constraints.maxHeight);
+
+        child.layout(context, innerConstraints);
+        assert(child.box != null);
+        totalHeight = math.max(totalHeight, child.box.height);
+      }
+      index++;
+    }
+
+    // Update Y positions
+    index = 0;
+    allocatedSize = 0;
+    for (Partition child in children) {
+      if (widths[index] > 0) {
+        final double offsetY = totalHeight - child.box.height;
+        child.box = PdfRect.fromPoints(
+            PdfPoint(allocatedSize, offsetY), child.box.size);
+        totalHeight = math.max(totalHeight, child.box.height);
+        allocatedSize += widths[index];
+      }
+      index++;
+    }
+
+    box = PdfRect(0, 0, allocatedSize, totalHeight);
+  }
+
+  @override
+  void paint(Context context) {
+    super.paint(context);
+
+    final Matrix4 mat = Matrix4.identity();
+    mat.translate(box.x, box.y);
+    context.canvas
+      ..saveContext()
+      ..setTransform(mat);
+    for (Partition child in children) {
+      child.paint(context);
+    }
+    context.canvas.restoreContext();
+  }
+
+  @override
+  void restoreContext(WidgetContext context) {
+    _context.apply(context);
+    int index = 0;
+    for (final Partition child in children) {
+      child.restoreContext(_context.partitionContext[index]);
+      index++;
+    }
+  }
+
+  @override
+  WidgetContext saveContext() {
+    int index = 0;
+    for (final Partition child in children) {
+      _context.partitionContext[index] = child.saveContext();
+      index++;
+    }
+    return _context;
+  }
+}

@@ -35,6 +35,7 @@ import 'widget_container_test.dart' as widget_container;
 import 'widget_flex_test.dart' as widget_flex;
 import 'widget_grid_view_test.dart' as widget_grid_view;
 import 'widget_multipage_test.dart' as widget_multipage;
+import 'widget_partitions_test.dart' as widget_partitions;
 import 'widget_table_test.dart' as widget_table;
 import 'widget_test.dart' as widget;
 import 'widget_text_test.dart' as widget_text;
@@ -62,6 +63,7 @@ void main() {
   widget_flex.main();
   widget_grid_view.main();
   widget_multipage.main();
+  widget_partitions.main();
   widget_table.main();
   widget_text.main();
   widget_theme.main();

+/*
+ * 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:pdf/widgets.dart';
+import 'package:test/test.dart';
+
+Document pdf;
+
+void main() {
+  setUpAll(() {
+    Document.debug = true;
+    pdf = Document();
+  });
+
+  test('Partitions Widget', () {
+    pdf.addPage(
+      MultiPage(
+        build: (Context context) => <Widget>[
+          Partitions(
+            children: <Partition>[
+              Partition(
+                flex: 1618,
+                child: Column(
+                  children: List<Widget>.generate(100, (int i) => Text('$i')),
+                ),
+              ),
+              Partition(
+                flex: 1000,
+                // width: 100,
+                child: Column(
+                  mainAxisAlignment: MainAxisAlignment.spaceEvenly,
+                  children: List<Widget>.generate(20, (int i) => Text('$i')),
+                ),
+              ),
+            ],
+          ),
+        ],
+      ),
+    );
+  });
+
+  tearDownAll(() {
+    final File file = File('widgets-partitions.pdf');
+    file.writeAsBytesSync(pdf.save());
+  });
+}