Make sampleSize apply to computeLabelSizes (#6926)

diff --git a/src/core/core.scale.js b/src/core/core.scale.js
index 022e3dd8e53be4b3f23913ca6ef46aa3cdc626a5..81fe4054a1895b9594ebf7fb0f953a358df0cb77 100644 (file)
--- a/src/core/core.scale.js
+++ b/src/core/core.scale.js
@@ -118,64 +118,6 @@ function garbageCollect(caches, length) {
        });
 }
 
-/**
- * Returns {width, height, offset} objects for the first, last, widest, highest tick
- * labels where offset indicates the anchor point offset from the top in pixels.
- */
-function computeLabelSizes(ctx, tickFonts, ticks, caches) {
-       const length = ticks.length;
-       const widths = [];
-       const heights = [];
-       const offsets = [];
-       let i, j, jlen, label, tickFont, fontString, cache, lineHeight, width, height, nestedLabel, widest, highest;
-
-       for (i = 0; i < length; ++i) {
-               label = ticks[i].label;
-               tickFont = ticks[i].major ? tickFonts.major : tickFonts.minor;
-               ctx.font = fontString = tickFont.string;
-               cache = caches[fontString] = caches[fontString] || {data: {}, gc: []};
-               lineHeight = tickFont.lineHeight;
-               width = height = 0;
-               // Undefined labels and arrays should not be measured
-               if (!isNullOrUndef(label) && !isArray(label)) {
-                       width = helpers.measureText(ctx, cache.data, cache.gc, width, label);
-                       height = lineHeight;
-               } else if (isArray(label)) {
-                       // if it is an array let's measure each element
-                       for (j = 0, jlen = label.length; j < jlen; ++j) {
-                               nestedLabel = label[j];
-                               // Undefined labels and arrays should not be measured
-                               if (!isNullOrUndef(nestedLabel) && !isArray(nestedLabel)) {
-                                       width = helpers.measureText(ctx, cache.data, cache.gc, width, nestedLabel);
-                                       height += lineHeight;
-                               }
-                       }
-               }
-               widths.push(width);
-               heights.push(height);
-               offsets.push(lineHeight / 2);
-       }
-       garbageCollect(caches, length);
-
-       widest = widths.indexOf(Math.max.apply(null, widths));
-       highest = heights.indexOf(Math.max.apply(null, heights));
-
-       function valueAt(idx) {
-               return {
-                       width: widths[idx] || 0,
-                       height: heights[idx] || 0,
-                       offset: offsets[idx] || 0
-               };
-       }
-
-       return {
-               first: valueAt(0),
-               last: valueAt(length - 1),
-               widest: valueAt(widest),
-               highest: valueAt(highest)
-       };
-}
-
 function getTickMarkLength(options) {
        return options.drawTicks ? options.tickMarkLength : 0;
 }
@@ -796,12 +738,80 @@ class Scale extends Element {
                let labelSizes = me._labelSizes;
 
                if (!labelSizes) {
-                       me._labelSizes = labelSizes = computeLabelSizes(me.ctx, parseTickFontOptions(me.options.ticks), me.ticks, me._longestTextCache);
+                       me._labelSizes = labelSizes = me._computeLabelSizes();
                }
 
                return labelSizes;
        }
 
+       /**
+        * Returns {width, height, offset} objects for the first, last, widest, highest tick
+        * labels where offset indicates the anchor point offset from the top in pixels.
+        * @private
+        */
+       _computeLabelSizes() {
+               const me = this;
+               const ctx = me.ctx;
+               const tickFonts = parseTickFontOptions(me.options.ticks);
+               const caches = me._longestTextCache;
+               const sampleSize = me.options.ticks.sampleSize;
+               const widths = [];
+               const heights = [];
+               const offsets = [];
+               let ticks = me.ticks;
+               if (sampleSize < ticks.length) {
+                       ticks = sample(ticks, sampleSize);
+               }
+               const length = ticks.length;
+               let i, j, jlen, label, tickFont, fontString, cache, lineHeight, width, height, nestedLabel, widest, highest;
+
+               for (i = 0; i < length; ++i) {
+                       label = ticks[i].label;
+                       tickFont = ticks[i].major ? tickFonts.major : tickFonts.minor;
+                       ctx.font = fontString = tickFont.string;
+                       cache = caches[fontString] = caches[fontString] || {data: {}, gc: []};
+                       lineHeight = tickFont.lineHeight;
+                       width = height = 0;
+                       // Undefined labels and arrays should not be measured
+                       if (!isNullOrUndef(label) && !isArray(label)) {
+                               width = helpers.measureText(ctx, cache.data, cache.gc, width, label);
+                               height = lineHeight;
+                       } else if (isArray(label)) {
+                               // if it is an array let's measure each element
+                               for (j = 0, jlen = label.length; j < jlen; ++j) {
+                                       nestedLabel = label[j];
+                                       // Undefined labels and arrays should not be measured
+                                       if (!isNullOrUndef(nestedLabel) && !isArray(nestedLabel)) {
+                                               width = helpers.measureText(ctx, cache.data, cache.gc, width, nestedLabel);
+                                               height += lineHeight;
+                                       }
+                               }
+                       }
+                       widths.push(width);
+                       heights.push(height);
+                       offsets.push(lineHeight / 2);
+               }
+               garbageCollect(caches, length);
+
+               widest = widths.indexOf(Math.max.apply(null, widths));
+               highest = heights.indexOf(Math.max.apply(null, heights));
+
+               function valueAt(idx) {
+                       return {
+                               width: widths[idx] || 0,
+                               height: heights[idx] || 0,
+                               offset: offsets[idx] || 0
+                       };
+               }
+
+               return {
+                       first: valueAt(0),
+                       last: valueAt(length - 1),
+                       widest: valueAt(widest),
+                       highest: valueAt(highest)
+               };
+       }
+
        /**
         * Used to get the label to display in the tooltip for the given value
         * @param value