From 7872c8490eb1bf8bb2fa173fc18216c2f5bb2d16 Mon Sep 17 00:00:00 2001
From: Evert Timberg <evert.timberg+github@gmail.com>
Date: Mon, 1 Jun 2020 08:07:48 -0400
Subject: [PATCH] Radial Linear Scale: Compute Value based on distance from
 center (#7449)

* Radial Linear Scale: Compute Value based on distance from center

* Code review updates
---
 src/scales/scale.radialLinear.js       | 10 ++++++++
 test/specs/scale.radialLinear.tests.js | 33 ++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/src/scales/scale.radialLinear.js b/src/scales/scale.radialLinear.js
index f8fb11fe4..0273394f8 100644
--- a/src/scales/scale.radialLinear.js
+++ b/src/scales/scale.radialLinear.js
@@ -422,6 +422,16 @@ class RadialLinearScale extends LinearScaleBase {
 		return (value - me.min) * scalingFactor;
 	}
 
+	getValueForDistanceFromCenter(distance) {
+		if (isNullOrUndef(distance)) {
+			return NaN;
+		}
+
+		const me = this;
+		const scaledDistance = distance / (me.drawingArea / (me.max - me.min));
+		return me.options.reverse ? me.max - scaledDistance : me.min + scaledDistance;
+	}
+
 	getPointPosition(index, distanceFromCenter) {
 		const me = this;
 		const angle = me.getIndexAngle(index) - (Math.PI / 2);
diff --git a/test/specs/scale.radialLinear.tests.js b/test/specs/scale.radialLinear.tests.js
index 240a2edd0..1e2268652 100644
--- a/test/specs/scale.radialLinear.tests.js
+++ b/test/specs/scale.radialLinear.tests.js
@@ -453,6 +453,39 @@ describe('Test the radial linear scale', function() {
 		expect(chart.scales.r.getDistanceFromCenterForValue(chart.scales.r.max)).toBe(0);
 	});
 
+	it('should get the correct value for a distance from the center point', function() {
+		var chart = window.acquireChart({
+			type: 'radar',
+			data: {
+				datasets: [{
+					data: [10, 5, 0, 25, 78]
+				}],
+				labels: ['label1', 'label2', 'label3', 'label4', 'label5']
+			},
+			options: {
+				scale: {
+					pointLabels: {
+						callback: function(value, index) {
+							return index.toString();
+						}
+					}
+				}
+			}
+		});
+
+		expect(chart.scales.r.getValueForDistanceFromCenter(0)).toBe(chart.scales.r.min);
+		expect(chart.scales.r.getValueForDistanceFromCenter(227)).toBe(chart.scales.r.max);
+
+		var dist = chart.scales.r.getDistanceFromCenterForValue(5);
+		expect(chart.scales.r.getValueForDistanceFromCenter(dist)).toBe(5);
+
+		chart.scales.r.options.reverse = true;
+		chart.update();
+
+		expect(chart.scales.r.getValueForDistanceFromCenter(0)).toBe(chart.scales.r.max);
+		expect(chart.scales.r.getValueForDistanceFromCenter(227)).toBe(chart.scales.r.min);
+	});
+
 	it('should correctly get angles for all points', function() {
 		var chart = window.acquireChart({
 			type: 'radar',
-- 
2.47.2