Implement vertical bar chart

@@ -5,6 +5,7 @@
 
 - Add textDirection parameter to PageTheme
 - Fix Bar graph offset
+- Implement vertical bar chart
 
 ## 1.11.2
 

@@ -30,9 +30,11 @@ class BarDataSet extends Dataset {
     this.surfaceOpacity = 1,
     this.width = 10,
     this.offset = 0,
+    this.axis = Axis.horizontal,
   })  : drawBorder = drawBorder ?? borderColor != null && color != borderColor,
         assert((drawBorder ?? borderColor != null && color != borderColor) ||
             drawSurface),
+        assert(axis != null),
         super(
           legend: legend,
           color: color,
@@ -51,11 +53,27 @@ class BarDataSet extends Dataset {
   final double width;
   final double offset;
 
+  final Axis axis;
+
   void _drawSurface(Context context, ChartGrid grid, LineChartValue value) {
+    switch (axis) {
+      case Axis.horizontal:
         final double y = (grid is CartesianGrid) ? grid.xAxisOffset : 0;
         final PdfPoint p = grid.toChart(value.point);
+        final double x = p.x + offset - width / 2;
+        final double height = p.y - y;
+
+        context.canvas.drawRect(x, y, width, height);
+        break;
+      case Axis.vertical:
+        final double x = (grid is CartesianGrid) ? grid.yAxisOffset : 0;
+        final PdfPoint p = grid.toChart(value.point);
+        final double y = p.y + offset - width / 2;
+        final double height = p.x - x;
 
-    context.canvas.drawRect(p.x + offset - width / 2, y, width, p.y - y);
+        context.canvas.drawRect(x, y, height, width);
+        break;
+    }
   }
 
   @override

@@ -191,6 +191,28 @@ void main() {
         ),
       ));
     });
+
+    test('Vertical BarChart', () {
+      pdf.addPage(Page(
+        pageFormat: PdfPageFormat.standard.landscape,
+        build: (Context context) => Chart(
+          grid: CartesianGrid(
+            xAxis: FixedAxis<int>(<int>[0, 1, 2, 3, 4, 5, 6]),
+            yAxis: FixedAxis<int>(<int>[0, 3, 6, 9], divisions: true),
+          ),
+          datasets: <Dataset>[
+            BarDataSet(
+              axis: Axis.vertical,
+              data: const <LineChartValue>[
+                LineChartValue(1, 1),
+                LineChartValue(2, 3),
+                LineChartValue(3, 7),
+              ],
+            ),
+          ],
+        ),
+      ));
+    });
   });
 
   tearDownAll(() {