Introduce "zero" shade orientation.

lib/timeline/component/graph2d_types/line.js

@@ -133,13 +133,17 @@ Line.prototype.draw = function (dataset, group, framework) {
       // append with points for fill and finalize the path
       if (group.options.shaded.enabled == true) {
         var fillPath = DOMutil.getSVGElement('path', framework.svgElements, framework.svg);
-        var dFill;
+        var zero = 0;
         if (group.options.shaded.orientation == 'top') {
-          dFill = 'M' + dataset[0].x + ',' + 0 + ' ' + d + 'L' + dataset[dataset.length - 1].x + ',' + 0;
+          zero = 0;
+        }
+        else if (group.options.shaded.orientation == 'bottom') {
+          zero = svgHeight;
         }
         else {
-          dFill = 'M' + dataset[0].x + ',' + svgHeight + ' ' + d + 'L' + dataset[dataset.length - 1].x + ',' + svgHeight;
+          zero = Math.min(Math.max(0,group.zeroPosition),svgHeight);
         }
+        var dFill = 'M' + dataset[0].x + ',' + zero + ' ' + d + 'L' + dataset[dataset.length - 1].x + ',' + zero;
         fillPath.setAttributeNS(null, 'class', group.className + ' vis-fill');
         if(group.options.shaded.style !== undefined) {
           fillPath.setAttributeNS(null, 'style', group.options.shaded.style);

lib/timeline/optionsGraph2d.js

@@ -33,7 +33,7 @@ let allOptions = {
   graphHeight: {string, number},
   shaded: {
     enabled: {boolean},
-    orientation: {string:['bottom','top']}, // top, bottom
+    orientation: {string:['bottom','top','zero']}, // top, bottom, zero
     __type__: {boolean,object}
   },
   style: {string:['line','bar','points']}, // line, bar
@@ -171,7 +171,7 @@ let configureOptions = {
     stack:false,
     shaded: {
       enabled: false,
-      orientation: ['top','bottom'] // top, bottom
+      orientation: ['zero','top','bottom'] // zero, top, bottom
     },
     style: ['line','bar','points'], // line, bar
     barChart: {
@@ -266,4 +266,4 @@ let configureOptions = {
   }
 };
 
-export {allOptions, configureOptions};
+export {allOptions, configureOptions};