Fix Bar graph offset

@@ -4,6 +4,7 @@
 ## 1.12.0
 
 - Add textDirection parameter to PageTheme
+- Fix Bar graph offset
 
 ## 1.11.2
 

@@ -25,12 +25,14 @@ class BarDataSet extends Dataset {
     this.borderColor,
     this.borderWidth = 1.5,
     PdfColor color = PdfColors.blue,
-    this.drawBorder = true,
+    bool drawBorder,
     this.drawSurface = true,
     this.surfaceOpacity = 1,
     this.width = 10,
     this.offset = 0,
-  })  : assert(drawBorder || drawSurface),
+  })  : drawBorder = drawBorder ?? borderColor != null && color != borderColor,
+        assert((drawBorder ?? borderColor != null && color != borderColor) ||
+            drawSurface),
         super(
           legend: legend,
           color: color,
@@ -53,7 +55,7 @@ class BarDataSet extends Dataset {
     final double y = (grid is CartesianGrid) ? grid.xAxisOffset : 0;
     final PdfPoint p = grid.toChart(value.point);
 
-    context.canvas.drawRect(p.x + offset - width / 2, y, width, p.y);
+    context.canvas.drawRect(p.x + offset - width / 2, y, width, p.y - y);
   }
 
   @override

@@ -170,6 +170,29 @@ void main() {
     });
   });
 
+  group('BarChart test', () {
+    test('Default 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(
+              data: const <LineChartValue>[
+                LineChartValue(1, 1),
+                LineChartValue(2, 3),
+                LineChartValue(3, 7),
+              ],
+            ),
+          ],
+        ),
+      ));
+    });
+  });
+
   tearDownAll(() {
     final File file = File('widgets-chart.pdf');
     file.writeAsBytesSync(pdf.save());