Use Excel-like axis calc for stacked with negative values

c3.js

@@ -12,7 +12,7 @@
         return c3;
     }
 
-    var injectedMethods = ['getAxisData', 'getAbscissa'];
+    var injectedMethods = ['getAxisData', 'getAbscissa', 'getAxisStackedData'];
 
     function Chart(config) {
         var $$ = this.internal = new ChartInternal(this);
@@ -5013,7 +5013,12 @@
                 if($$.config.is_xy){
                     sizesX = $$.getAbscissa($$.config.ed3Type, minmax.minX, minmax.maxX);
                 }
-                sizesY = $$.getAxisData(minmax.minY, minmax.maxY);
+
+                if($$.config.normalized){
+                    sizesY = $$.getAxisStackedData(minmax.minY, minmax.maxY);
+                } else {
+                    sizesY = $$.getAxisData(minmax.minY, minmax.maxY);
+                }
             } else {
                 sizesY = {
                     min: minmax.minY,
@@ -5028,18 +5033,6 @@
                 sizesY.min = Math.max(sizesY.min, -1);
             }
 
-            if($$.config.normalized){
-                if(sizesY.min < 0 && minmax.minY < 0){
-                    while(sizesY.min < minmax.minY){
-                        sizesY.min += sizesY.step;
-                    }
-
-                    if(sizesY.min >= minmax.minY){
-                        sizesY.min -= sizesY.step;
-                    }
-                }
-            }
-
             $$.api.axis.range({
                 min: {
                     x: sizesX ? sizesX.min : undefined,

src/axis.js

@@ -401,7 +401,12 @@ c3_chart_internal_fn.tuneAxis = function(sync, callback){
             if($$.config.is_xy){
                 sizesX = $$.getAbscissa($$.config.ed3Type, minmax.minX, minmax.maxX);
             }
-            sizesY = $$.getAxisData(minmax.minY, minmax.maxY);
+
+            if($$.config.normalized){
+                sizesY = $$.getAxisStackedData(minmax.minY, minmax.maxY);
+            } else {
+                sizesY = $$.getAxisData(minmax.minY, minmax.maxY);
+            }
         } else {
             sizesY = {
                 min: minmax.minY,
@@ -416,18 +421,6 @@ c3_chart_internal_fn.tuneAxis = function(sync, callback){
             sizesY.min = Math.max(sizesY.min, -1);
         }
 
-        if($$.config.normalized){
-            if(sizesY.min < 0 && minmax.minY < 0){
-                while(sizesY.min < minmax.minY){
-                    sizesY.min += sizesY.step;
-                }
-
-                if(sizesY.min >= minmax.minY){
-                    sizesY.min -= sizesY.step;
-                }
-            }
-        }
-
         $$.api.axis.range({
             min: {
                 x: sizesX ? sizesX.min : undefined,

src/core.js

@@ -7,7 +7,7 @@ var c3init = function(module){
     return c3;
 }
 
-var injectedMethods = ['getAxisData', 'getAbscissa'];
+var injectedMethods = ['getAxisData', 'getAbscissa', 'getAxisStackedData'];
 
 function Chart(config) {
     var $$ = this.internal = new ChartInternal(this);