From b21c74eaee64bdc31321dcadb49d0d35fbc7f251 Mon Sep 17 00:00:00 2001
From: etimberg <evert.timberg@gmail.com>
Date: Sun, 21 Jan 2018 10:23:25 -0500
Subject: [PATCH] Treat negative values in doughnut charts as positive

---
 src/controllers/controller.doughnut.js  |  2 +-
 test/specs/controller.doughnut.tests.js | 40 +++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/src/controllers/controller.doughnut.js b/src/controllers/controller.doughnut.js
index 6028602c472..f7b36e989a9 100644
--- a/src/controllers/controller.doughnut.js
+++ b/src/controllers/controller.doughnut.js
@@ -273,7 +273,7 @@ module.exports = function(Chart) {
 		calculateCircumference: function(value) {
 			var total = this.getMeta().total;
 			if (total > 0 && !isNaN(value)) {
-				return (Math.PI * 2.0) * (value / total);
+				return (Math.PI * 2.0) * (Math.abs(value) / total);
 			}
 			return 0;
 		},
diff --git a/test/specs/controller.doughnut.tests.js b/test/specs/controller.doughnut.tests.js
index 85e382ac3f9..a4d6526c912 100644
--- a/test/specs/controller.doughnut.tests.js
+++ b/test/specs/controller.doughnut.tests.js
@@ -205,6 +205,46 @@ describe('Chart.controllers.doughnut', function() {
 		});
 	});
 
+	it('should treat negative values as positive', function() {
+		var chart = window.acquireChart({
+			type: 'doughnut',
+			data: {
+				datasets: [{
+					data: [-1, -3]
+				}],
+				labels: ['label0', 'label1']
+			},
+			options: {
+				legend: false,
+				title: false,
+				cutoutPercentage: 50,
+				rotation: Math.PI,
+				circumference: Math.PI * 0.5,
+				elements: {
+					arc: {
+						backgroundColor: 'rgb(255, 0, 0)',
+						borderColor: 'rgb(0, 0, 255)',
+						borderWidth: 2
+					}
+				}
+			}
+		});
+
+		var meta = chart.getDatasetMeta(0);
+
+		expect(meta.data.length).toBe(2);
+
+		// Only startAngle, endAngle and circumference should be different.
+		[
+			{c: Math.PI / 8, s: Math.PI, e: Math.PI + Math.PI / 8},
+			{c: 3 * Math.PI / 8, s: Math.PI + Math.PI / 8, e: Math.PI + Math.PI / 2}
+		].forEach(function(expected, i) {
+			expect(meta.data[i]._model.circumference).toBeCloseTo(expected.c, 8);
+			expect(meta.data[i]._model.startAngle).toBeCloseTo(expected.s, 8);
+			expect(meta.data[i]._model.endAngle).toBeCloseTo(expected.e, 8);
+		});
+	});
+
 	it ('should draw all arcs', function() {
 		var chart = window.acquireChart({
 			type: 'doughnut',