handle auto rotation in pie and reuse rotation function

Author: archmoj

src/traces/pie/helpers.js

@@ -40,3 +40,7 @@ exports.castOption = function castOption(item, indices) {
     if(Array.isArray(item)) return exports.getFirstFilled(item, indices);
     else if(item) return item;
 };
+
+exports.getRotationAngle = function(rotation) {
+    return (rotation === 'auto' ? 0 : rotation) * Math.PI / 180;
+};

src/traces/pie/plot.js

@@ -1045,7 +1045,7 @@ function setCoords(cd) {
     var cd0 = cd[0];
     var r = cd0.r;
     var trace = cd0.trace;
-    var currentAngle = trace.rotation * Math.PI / 180;
+    var currentAngle = helpers.getRotationAngle(trace.rotation);
     var angleFactor = 2 * Math.PI / cd0.vTotal;
     var firstPt = 'px0';
     var lastPt = 'px1';

src/traces/sunburst/plot.js

@@ -18,6 +18,7 @@ var uniformText = require('../bar/uniform_text');
 var recordMinTextSize = uniformText.recordMinTextSize;
 var clearMinTextSize = uniformText.clearMinTextSize;
 var piePlot = require('../pie/plot');
+var getRotationAngle = require('../pie/helpers').getRotationAngle;
 var computeTransform = piePlot.computeTransform;
 var transformInsideText = piePlot.transformInsideText;
 var styleOne = require('./style').styleOne;
@@ -150,11 +151,11 @@ function plotOne(gd, cd, element, transitionOpts) {
     // filter out slices that won't show up on graph
     sliceData = sliceData.filter(function(pt) { return pt.y1 <= cutoff; });
 
-    if(trace.rotation && trace.rotation !== 'auto') {
-        var extraAngle = trace.rotation * Math.PI / 180;
+    var baseX = getRotationAngle(trace.rotation);
+    if(baseX) {
         sliceData.forEach(function(pt) {
-            pt.x0 += extraAngle;
-            pt.x1 += extraAngle;
+            pt.x0 += baseX;
+            pt.x1 += baseX;
         });
     }