From cf3491299668b99b27a93746bea882ad338fcac9 Mon Sep 17 00:00:00 2001
From: Evert Timberg <evert.timberg@gmail.com>
Date: Sat, 4 Jan 2020 19:05:37 -0500
Subject: [PATCH] Title alignment options work with overall legend alignment

---
 samples/legend/title.html    | 11 +++++--
 src/plugins/plugin.legend.js | 62 ++++++++++++++++++++++++++++++------
 2 files changed, 61 insertions(+), 12 deletions(-)

diff --git a/samples/legend/title.html b/samples/legend/title.html
index d9fc04ab182..7f5e334ecea 100644
--- a/samples/legend/title.html
+++ b/samples/legend/title.html
@@ -48,7 +48,7 @@
 	</div>
 	<script>
 		var color = Chart.helpers.color;
-		function createConfig(legendPosition, titlePosition, colorName) {
+		function createConfig(legendPosition, titlePosition, align, colorName) {
 			return {
 				type: 'line',
 				data: {
@@ -72,6 +72,7 @@
 				options: {
 					responsive: true,
 					legend: {
+						align: align,
 						position: legendPosition,
 						title: {
 							display: true,
@@ -106,37 +107,43 @@
 		window.onload = function() {
 			[{
 				id: 'chart-legend-top-start',
+				align: 'start',
 				legendPosition: 'top',
 				titlePosition: 'start',
 				color: 'red'
 			}, {
 				id: 'chart-legend-top-center',
+				align: 'center',
 				legendPosition: 'top',
 				titlePosition: 'center',
 				color: 'orange'
 			}, {
 				id: 'chart-legend-top-end',
+				align: 'end',
 				legendPosition: 'top',
 				titlePosition: 'end',
 				color: 'yellow'
 			}, {
 				id: 'chart-legend-left-start',
+				align: 'start',
 				legendPosition: 'left',
 				titlePosition: 'start',
 				color: 'green'
 			}, {
 				id: 'chart-legend-left-center',
+				align: 'center',
 				legendPosition: 'left',
 				titlePosition: 'center',
 				color: 'blue'
 			}, {
 				id: 'chart-legend-left-end',
+				align: 'end',
 				legendPosition: 'left',
 				titlePosition: 'end',
 				color: 'purple'
 			}].forEach(function(details) {
 				var ctx = document.getElementById(details.id).getContext('2d');
-				var config = createConfig(details.legendPosition, details.titlePosition, details.color);
+				var config = createConfig(details.legendPosition, details.titlePosition, details.align, details.color);
 				new Chart(ctx, config);
 			});
 		};
diff --git a/src/plugins/plugin.legend.js b/src/plugins/plugin.legend.js
index 9a2a3dcdd2f..5910dea777d 100644
--- a/src/plugins/plugin.legend.js
+++ b/src/plugins/plugin.legend.js
@@ -528,15 +528,60 @@ class Legend extends Element {
 		const position = titleOpts.position;
 		let x, textAlign;
 
-		if (position === 'start') {
-			x = me.left + titlePadding.left;
+		const halfFontSize = titleFont.size / 2;
+		let y = me.top + titlePadding.top + halfFontSize;
+
+		// These defaults are used when the legend is vertical.
+		// When horizontal, they are computed below.
+		let left = me.left;
+		let maxWidth = me.width;
+
+		if (this.isHorizontal()) {
+			// Move left / right so that the title is above the legend lines
+			maxWidth = Math.max(...me.lineWidths);
+			switch (opts.align) {
+			case 'start':
+				// x is already correct in this case
+				left = me.left;
+				break;
+			case 'end':
+				left = me.right - maxWidth;
+				break;
+			default:
+				left = ((me.left + me.right) / 2) - (maxWidth / 2);
+				break;
+			}
+		} else {
+			// Move down so that the title is above the legend stack in every alignment
+			const maxHeight = Math.max(...me.columnHeights);
+			switch (opts.align) {
+			case 'start':
+				// y is already correct in this case
+				break;
+			case 'end':
+				y += me.height - maxHeight;
+				break;
+			default: // center
+				y += (me.height - maxHeight) / 2;
+				break;
+			}
+		}
+
+		// Now that we know the left edge of the inner legend box, compute the correct
+		// X coordinate from the title alignment
+		switch (position) {
+		case 'start':
+			x = left;
 			textAlign = 'left';
-		} else if (position === 'center') {
-			x = (me.left + me.right) / 2;
-			textAlign = 'center';
-		} else if (position === 'end') {
-			x = me.right - titlePadding.right;
+			break;
+		case 'end':
+			x = left + maxWidth;
 			textAlign = 'right';
+			break;
+		default:
+			x = left + (maxWidth / 2);
+			textAlign = 'center';
+			break;
 		}
 
 		// Canvas setup
@@ -546,9 +591,6 @@ class Legend extends Element {
 		ctx.fillStyle = fontColor;
 		ctx.font = titleFont.string;
 
-		// Draw the title text
-		const halfFontSize = titleFont.size / 2;
-		const y = me.top + titlePadding.top + halfFontSize;
 		ctx.fillText(titleOpts.text, x, y);
 	}