From 334ba44e95224dc14ea4919e6c1f467d264e250d Mon Sep 17 00:00:00 2001
From: Tanner Linsley <tannerlinsley@gmail.com>
Date: Sat, 31 Oct 2015 22:45:25 -0600
Subject: [PATCH] Allow line controller to calculate stacked values

---
 src/controllers/controller.line.js | 35 +++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/src/controllers/controller.line.js b/src/controllers/controller.line.js
index e034e325c..954686e06 100644
--- a/src/controllers/controller.line.js
+++ b/src/controllers/controller.line.js
@@ -193,7 +193,7 @@
 				// Desired view properties
 				_model: {
 					x: xScale.getPixelForValue(this.getDataset().data[index], index, this.index, this.chart.isCombo),
-					y: reset ? scaleBase : yScale.getPixelForValue(this.getDataset().data[index], index, this.index),
+					y: reset ? scaleBase : this.calculatePointY(this.getDataset().data[index], index, this.index, this.chart.isCombo),
 					// Appearance
 					tension: point.custom && point.custom.tension ? point.custom.tension : (this.getDataset().tension || this.chart.options.elements.line.tension),
 					radius: point.custom && point.custom.radius ? point.custom.radius : helpers.getValueAtIndexOrDefault(this.getDataset().radius, index, this.chart.options.elements.point.radius),
@@ -208,6 +208,39 @@
 			point._model.skip = point.custom && point.custom.skip ? point.custom.skip : (isNaN(point._model.x) || isNaN(point._model.y));
 		},
 
+		calculatePointY: function(value, index, datasetIndex, isCombo) {
+
+			var xScale = this.getScaleForId(this.getDataset().xAxisID);
+			var yScale = this.getScaleForId(this.getDataset().yAxisID);
+
+			if (yScale.options.stacked) {
+
+				var sumPos = 0,
+					sumNeg = 0;
+
+				for (var i = this.chart.data.datasets.length - 1; i > datasetIndex; i--) {
+					var ds = this.chart.data.datasets[i];
+					if (helpers.isDatasetVisible(ds)) {
+						if (ds.data[index] < 0) {
+							sumNeg += ds.data[index] || 0;
+						} else {
+							sumPos += ds.data[index] || 0;
+						}
+					}
+				}
+
+				if (value < 0) {
+					return yScale.getPixelForValue(sumNeg + value);
+				} else {
+					return yScale.getPixelForValue(sumPos + value);
+				}
+
+				return yScale.getPixelForValue(value);
+			}
+
+			return yScale.getPixelForValue(value);
+		},
+
 		updateBezierControlPoints: function() {
 			// Update bezier control points
 			helpers.each(this.getDataset().metaData, function(point, index) {