Improve autoSkip performance

src/core/core.scale.js

@@ -304,11 +304,13 @@ var Scale = Element.extend({
 			ticks = [];
 			for (i = 0, ilen = me.ticks.length; i < ilen; ++i) {
 				ticks.push({
+					index: i,
 					value: me.ticks[i],
 					major: false
 				});
 			}
 		}
+		me._numTicks = ticks.length;
 
 		me.beforeTickToLabelConversion();
 
@@ -422,13 +424,13 @@ var Scale = Element.extend({
 		var me = this;
 		var options = me.options;
 		var tickOpts = options.ticks;
-		var ticks = me.getTicks();
 		var minRotation = tickOpts.minRotation || 0;
 		var maxRotation = tickOpts.maxRotation;
 		var labelRotation = minRotation;
+		var numTicks = me._numTicks;
 		var labelSizes, maxLabelWidth, maxLabelHeight, maxWidth, tickWidth, maxHeight, maxLabelDiagonal;
 
-		if (!me._isVisible() || !tickOpts.display || minRotation >= maxRotation || ticks.length <= 1 || !me.isHorizontal()) {
+		if (!me._isVisible() || !tickOpts.display || minRotation >= maxRotation || numTicks <= 1 || !me.isHorizontal()) {
 			me.labelRotation = minRotation;
 			return;
 		}
@@ -440,11 +442,11 @@ var Scale = Element.extend({
 		// Estimate the width of each grid based on the canvas width, the maximum
 		// label width and the number of tick intervals
 		maxWidth = Math.min(me.maxWidth, me.chart.width - maxLabelWidth);
-		tickWidth = options.offset ? me.maxWidth / ticks.length : maxWidth / (ticks.length - 1);
+		tickWidth = options.offset ? me.maxWidth / numTicks : maxWidth / (numTicks - 1);
 
 		// Allow 3 pixels x2 padding either side for label readability
 		if (maxLabelWidth + 6 > tickWidth) {
-			tickWidth = maxWidth / (ticks.length - (options.offset ? 0.5 : 1));
+			tickWidth = maxWidth / (numTicks - (options.offset ? 0.5 : 1));
 			maxHeight = me.maxHeight - getTickMarkLength(options.gridLines)
 				- tickOpts.padding - getScaleLabelHeight(options.scaleLabel);
 			maxLabelDiagonal = Math.sqrt(maxLabelWidth * maxLabelWidth + maxLabelHeight * maxLabelHeight);
@@ -475,7 +477,6 @@ var Scale = Element.extend({
 		};
 
 		var chart = me.chart;
-		var ticks = me.getTicks();
 		var opts = me.options;
 		var tickOpts = opts.ticks;
 		var scaleLabelOpts = opts.scaleLabel;
@@ -523,7 +524,7 @@ var Scale = Element.extend({
 				minSize.height = Math.min(me.maxHeight, minSize.height + labelHeight + tickPadding);
 
 				var offsetLeft = me.getPixelForTick(0) - me.left;
-				var offsetRight = me.right - me.getPixelForTick(ticks.length - 1);
+				var offsetRight = me.right - me.getPixelForTick(me._numTicks - 1);
 				var paddingLeft, paddingRight;
 
 				// Ensure that our ticks are always inside the canvas. When rotated, ticks are right aligned
@@ -704,7 +705,7 @@ var Scale = Element.extend({
 	getPixelForTick: function(index) {
 		var me = this;
 		var offset = me.options.offset;
-		var numTicks = me._ticks.length;
+		var numTicks = me._numTicks;
 		if (index < 0 || index > numTicks - 1) {
 			return null;
 		}
@@ -786,11 +787,9 @@ var Scale = Element.extend({
 		for (i = 0; i < tickCount; i++) {
 			tick = ticks[i];
 
-			if (skipRatio > 1 && i % skipRatio > 0) {
-				// leave tick in place but make sure it's not displayed (#4635)
-				delete tick.label;
+			if (skipRatio <= 1 || i % skipRatio === 0) {
+				result.push(tick);
 			}
-			result.push(tick);
 		}
 		return result;
 	},
@@ -895,12 +894,8 @@ var Scale = Element.extend({
 			tickEnd = me.left + tl;
 		}
 
-		helpers.each(ticks, function(tick, index) {
-			// autoskipper skipped this tick (#4635)
-			if (helpers.isNullOrUndef(tick.label)) {
-				return;
-			}
-
+		helpers.each(ticks, function(tick) {
+			var index = tick.index;
 			var label = tick.label;
 			var tickFont = tick.major ? tickFonts.major : tickFonts.minor;
 			var lineHeight = tickFont.lineHeight;

src/scales/scale.category.js

@@ -60,7 +60,7 @@ module.exports = Scale.extend({
 			return me.getRightValue(chart.data.datasets[datasetIndex].data[index]);
 		}
 
-		return me.ticks[index - me.minIndex];
+		return me._getLabels()[index];
 	},
 
 	// Used to get data value locations.  Value can either be an index or a numerical value

src/scales/scale.time.js

@@ -430,6 +430,7 @@ function ticksFromTimestamps(scale, values, majorUnit) {
 		map[value] = i;
 
 		ticks.push({
+			index: i,
 			value: value,
 			major: false
 		});

test/specs/core.scale.tests.js

@@ -34,12 +34,6 @@ describe('Core.scale', function() {
 			});
 		}
 
-		function lastTick(chart) {
-			var xAxis = chart.scales['x-axis-0'];
-			var ticks = xAxis.getTicks();
-			return ticks[ticks.length - 1];
-		}
-
 		it('should display the last tick if it fits evenly with other ticks', function() {
 			var chart = getChart({
 				labels: [
@@ -52,7 +46,7 @@ describe('Core.scale', function() {
 				}]
 			});
 
-			expect(lastTick(chart).label).toEqual('September 2018');
+			expect(chart.scales['x-axis-0']._ticks.length).toEqual(9);
 		});
 
 		it('should not display the last tick if it does not fit evenly', function() {
@@ -71,7 +65,7 @@ describe('Core.scale', function() {
 				}]
 			});
 
-			expect(lastTick(chart).label).toBeUndefined();
+			expect(chart.scales['x-axis-0']._ticks.length).toEqual(13);
 		});
 	});