Allow setting the max pie-chart angle

PhilJay/MPAndroidChart#989

Charts/Classes/Charts/PieChartView.swift

@@ -25,6 +25,9 @@ public class PieChartView: PieRadarChartViewBase
 
     /// array that holds the absolute angle in degrees of each slice
     private var _absoluteAngles = [CGFloat]()
+
+    /// maximum angle for this pie
+    private var _maxAngle: CGFloat = 360.0
 
     public override init(frame: CGRect)
     {
@@ -192,7 +195,7 @@ public class PieChartView: PieRadarChartViewBase
     /// calculates the needed angle for a given value
     private func calcAngle(value: Double) -> CGFloat
     {
-        return CGFloat(value) / CGFloat(_data.yValueSum) * 360.0
+        return CGFloat(value) / CGFloat(_data.yValueSum) * _maxAngle
     }
 
     public override func indexForAngle(angle: CGFloat) -> Int
@@ -503,4 +506,29 @@ public class PieChartView: PieRadarChartViewBase
             setNeedsDisplay()
         }
     }
+
+    /// The max angle that is used for calculating the pie-circle.
+    /// 360 means it's a full pie-chart, 180 results in a half-pie-chart.
+    /// - default: 360.0
+    public var maxAngle: CGFloat
+    {
+        get
+        {
+            return _maxAngle
+        }
+        set
+        {
+            _maxAngle = newValue
+
+            if _maxAngle > 360.0
+            {
+                _maxAngle = 360.0
+            }
+
+            if _maxAngle < 90.0
+            {
+                _maxAngle = 90.0
+            }
+        }
+    }
 }