Add support for negative values for stacked-100

src/axis.js

@@ -381,8 +381,10 @@ c3_chart_internal_fn.tuneAxis = function(sync, callback){
     // if we don't need to tune
     if($$.config.normalized){
         $$.data.targets = $$.normalize($$.data._targets);
-        $$.cachedRedraw();
-        return;
+        if($$.data.targets.noNegative){
+            $$.cachedRedraw();
+            return;
+        }
     }
         
     var apply = function(){

src/stacked.js

@@ -6,6 +6,8 @@ c3.chart.internal.fn.normalize = function(targets){
     }
 
     var data = [];
+    
+    data.noNegative = true;
 
     targets.forEach(function(target){
         data.push($$.cloneTarget(target));
@@ -14,7 +16,12 @@ c3.chart.internal.fn.normalize = function(targets){
     for(var k = 0; k < targets[0].values.length; k++) {
         var tt = 0;
         for(c in targets) {
-            tt = tt + targets[c].values[k].value;
+            if(targets[c].values[k]){
+                if(targets[c].values[k].value < 0){
+                    data.noNegative = false;
+                }
+                tt = tt + Math.abs(targets[c].values[k].value);
+            }
         }
         tr[k] = tt;
     }