Move turning angle

src/api.chart.js

@@ -57,3 +57,25 @@ c3_chart_fn.bgcolor = function(value) {
         svg.style.backgroundColor = value;
     }              
 };  
+
+c3.chart.fn.turn = function(options){
+    var $$ = this.internal;         
+    var turnAngle;
+
+    if(!options){
+        return;  
+    }
+
+    if(options.radians){            
+        turnAngle = options.radians;    
+    } else {     
+        turnAngle = toRadians(options.degrees);
+    }            
+
+    if(options.relative){           
+        $$.config.turnAngle += turnAngle;
+    } else {     
+        $$.config.turnAngle = turnAngle;
+    }
+};
+

src/arc.js

@@ -45,6 +45,12 @@ c3_chart_internal_fn.updateAngle = function (d) {
         d.startAngle = -1 * (Math.PI / 2);
         d.endAngle = d.startAngle + gTic * gValue;
     }
+
+    if(config.turnAngle){
+        d.endAngle += config.turnAngle;
+        d.startAngle += config.turnAngle;
+    }
+
     return found ? d : null;
 };
 

src/util.js

@@ -43,4 +43,11 @@ var isValue = c3_chart_internal_fn.isValue = function (v) {
             items = [path.pathSegList.getItem(0), path.pathSegList.getItem(1)],
             minX = items[0].x, minY = Math.min(items[0].y, items[1].y);
         return {x: minX, y: minY, width: box.width, height: box.height};
+    },
+    toRadians = function(degrees){
+        return degrees * (Math.PI / 180);
+    },
+    toDegrees = function(radians){
+        return radians * (180 / Math.PI);
     };
+