From: etimberg <evert.timberg@gmail.com>
Date: Sat, 26 Nov 2016 17:29:15 +0000 (-0500)
Subject: Fix monotone cubic interpolation when two adjacent points are at the exact same x... 
X-Git-Tag: v2.5.0~1^2~40
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=7a8f20e88fb2029e82c9903be99412878368405a;p=thirdparty%2FChart.js.git

Fix monotone cubic interpolation when two adjacent points are at the exact same x pixel value
---

diff --git a/src/core/core.helpers.js b/src/core/core.helpers.js
index 542088f61..506ad9003 100644
--- a/src/core/core.helpers.js
+++ b/src/core/core.helpers.js
@@ -361,7 +361,10 @@ module.exports = function(Chart) {
 			pointBefore = i > 0 ? pointsWithTangents[i - 1] : null;
 			pointAfter = i < pointsLen - 1 ? pointsWithTangents[i + 1] : null;
 			if (pointAfter && !pointAfter.model.skip) {
-				pointCurrent.deltaK = (pointAfter.model.y - pointCurrent.model.y) / (pointAfter.model.x - pointCurrent.model.x);
+				var slopeDeltaX = (pointAfter.model.x - pointCurrent.model.x);
+
+				// In the case of two points that appear at the same x pixel, slopeDeltaX is 0
+				pointCurrent.deltaK = slopeDeltaX !== 0 ? (pointAfter.model.y - pointCurrent.model.y) / slopeDeltaX : 0;
 			}
 
 			if (!pointBefore || pointBefore.model.skip) {
diff --git a/test/core.helpers.tests.js b/test/core.helpers.tests.js
index 4cd200ae3..75e0baf90 100644
--- a/test/core.helpers.tests.js
+++ b/test/core.helpers.tests.js
@@ -412,6 +412,7 @@ describe('Core helper tests', function() {
 			{_model: {x: 27, y: 125, skip: false}},
 			{_model: {x: 30, y: 105, skip: false}},
 			{_model: {x: 33, y: 110, skip: false}},
+			{_model: {x: 33, y: 110, skip: false}},
 			{_model: {x: 36, y: 170, skip: false}}
 		];
 		helpers.splineCurveMonotone(dataPoints);
@@ -532,9 +533,20 @@ describe('Core helper tests', function() {
 				y: 110,
 				skip: false,
 				controlPointPreviousX: 32,
-				controlPointPreviousY: 105,
+				controlPointPreviousY: 110,
+				controlPointNextX: 33,
+				controlPointNextY: 110
+			}
+		},
+		{
+			_model: {
+				x: 33,
+				y: 110,
+				skip: false,
+				controlPointPreviousX: 33,
+				controlPointPreviousY: 110,
 				controlPointNextX: 34,
-				controlPointNextY: 115
+				controlPointNextY: 110
 			}
 		},
 		{