Fix appending data while decimation is active

src/controllers/controller.line.js

@@ -75,7 +75,7 @@ export default class LineController extends DatasetController {
 
   updateElements(points, start, count, mode) {
     const reset = mode === 'reset';
-    const {iScale, vScale, _stacked, _dataset} = this._cachedMeta;
+    const {iScale, vScale, _stacked} = this._cachedMeta;
     const {sharedOptions, includeOptions} = this._getSharedOptions(start, mode);
     const iAxis = iScale.axis;
     const vAxis = vScale.axis;
@@ -104,7 +104,7 @@ export default class LineController extends DatasetController {
       properties.stop = i > 0 && (Math.abs(parsed[iAxis] - prevParsed[iAxis])) > maxGapLength;
       if (segment) {
         properties.parsed = parsed;
-        properties.raw = _dataset.data[i];
+        properties.raw = this._data[i];
       }
 
       if (includeOptions) {

src/controllers/controller.scatter.js

@@ -110,7 +110,7 @@ export default class ScatterController extends DatasetController {
 
   updateElements(points, start, count, mode) {
     const reset = mode === 'reset';
-    const {iScale, vScale, _stacked, _dataset} = this._cachedMeta;
+    const {iScale, vScale, _stacked} = this._cachedMeta;
     const firstOpts = this.resolveDataElementOptions(start, mode);
     const sharedOptions = this.getSharedOptions(firstOpts);
     const includeOptions = this.includeOptions(mode, sharedOptions);
@@ -133,7 +133,7 @@ export default class ScatterController extends DatasetController {
       properties.stop = i > 0 && (Math.abs(parsed[iAxis] - prevParsed[iAxis])) > maxGapLength;
       if (segment) {
         properties.parsed = parsed;
-        properties.raw = _dataset.data[i];
+        properties.raw = this._data[i];
       }
 
       if (includeOptions) {

src/core/core.datasetController.js

@@ -364,7 +364,7 @@ export default class DatasetController {
 	 */
   _dataCheck() {
     const dataset = this.getDataset();
-    const data = dataset.data || (dataset.data = []);
+    const data = dataset._decimated || dataset.data || (dataset.data = []);
     const _data = this._data;
 
     // In order to correctly handle data addition/deletion animation (and thus simulate
@@ -767,7 +767,7 @@ export default class DatasetController {
       context = element.$context ||
         (element.$context = createDataContext(this.getContext(), index, element));
       context.parsed = this.getParsed(index);
-      context.raw = dataset.data[index];
+      context.raw = this._data[index];
       context.index = context.dataIndex = index;
     } else {
       context = this.$context ||

src/plugins/plugin.decimation.js

@@ -248,15 +248,15 @@ export default {
 
       if (isNullOrUndef(_data)) {
         // First time we are seeing this dataset
-        // We override the 'data' property with a setter that stores the
-        // raw data in _data, but reads the decimated data from _decimated
+        // We override the 'data' property with an accessor that stores and
+        // reads the raw data in _data. Dataset controllers use _decimated.
         dataset._data = data;
         delete dataset.data;
         Object.defineProperty(dataset, 'data', {
           configurable: true,
           enumerable: true,
           get: function() {
-            return this._decimated;
+            return this._data;
           },
           set: function(d) {
             this._data = d;

src/plugins/plugin.tooltip.js

@@ -133,7 +133,7 @@ function createTooltipItem(chart, item) {
     chart,
     label,
     parsed: controller.getParsed(index),
-    raw: chart.data.datasets[datasetIndex].data[index],
+    raw: controller._data[index],
     formattedValue: value,
     dataset: controller.getDataset(),
     dataIndex: index,

test/specs/plugin.decimation.tests.js

@@ -51,7 +51,7 @@ describe('Plugin.decimation', function() {
         }
       });
 
-      expect(chart.data.datasets[0].data.length).toBe(10);
+      expect(chart.getDatasetMeta(0).data.length).toBe(10);
     });
 
     it('should draw the specified number of elements based on canvas width', function() {
@@ -91,7 +91,7 @@ describe('Plugin.decimation', function() {
         }
       });
 
-      expect(chart.data.datasets[0].data.length).toBe(7);
+      expect(chart.getDatasetMeta(0).data.length).toBe(7);
     });
 
     it('should draw the specified number of elements based on threshold', function() {
@@ -130,7 +130,59 @@ describe('Plugin.decimation', function() {
         }
       });
 
-      expect(chart.data.datasets[0].data.length).toBe(5);
+      expect(chart.getDatasetMeta(0).data.length).toBe(5);
+    });
+
+    it('should append data after decimation', function() {
+      const data = originalData.slice();
+      const point = {x: 10, y: 10};
+      var chart = window.acquireChart({
+        type: 'line',
+        data: {
+          datasets: [{
+            data,
+            label: 'dataset1'
+          }]
+        },
+        options: {
+          parsing: false,
+          scales: {
+            x: {
+              type: 'linear'
+            }
+          },
+          plugins: {
+            decimation: {
+              enabled: true,
+              algorithm: 'lttb',
+              samples: 5,
+              threshold: 7
+            }
+          }
+        }
+      }, {
+        canvas: {
+          height: 100,
+          width: 100
+        },
+        wrapper: {
+          height: 100,
+          width: 100
+        }
+      });
+
+      chart.data.datasets[0].data.push(point);
+      chart.update();
+
+      expect(data.length).toBe(11);
+      const meta = chart.getDatasetMeta(0);
+      const parsed = meta._parsed;
+      expect(parsed[parsed.length - 1]).toBe(point);
+      expect(meta.controller.getContext(parsed.length - 1).raw).toBe(point);
+
+      chart.tooltip.setActiveElements([{datasetIndex: 0, index: parsed.length - 1}], {x: 0, y: 0});
+      chart.update();
+      expect(chart.tooltip.dataPoints[0].raw).toBe(point);
     });
 
     it('should draw all element only in range', function() {
@@ -172,12 +224,13 @@ describe('Plugin.decimation', function() {
 
       // Data range is 4 (3->6) and the first point is added
       const expectedPoints = 5;
-      expect(chart.data.datasets[0].data.length).toBe(expectedPoints);
-      expect(chart.data.datasets[0].data[0].x).toBe(originalData[2].x);
-      expect(chart.data.datasets[0].data[1].x).toBe(originalData[3].x);
-      expect(chart.data.datasets[0].data[2].x).toBe(originalData[4].x);
-      expect(chart.data.datasets[0].data[3].x).toBe(originalData[5].x);
-      expect(chart.data.datasets[0].data[4].x).toBe(originalData[6].x);
+      const parsed = chart.getDatasetMeta(0)._parsed;
+      expect(parsed.length).toBe(expectedPoints);
+      expect(parsed[0].x).toBe(originalData[2].x);
+      expect(parsed[1].x).toBe(originalData[3].x);
+      expect(parsed[2].x).toBe(originalData[4].x);
+      expect(parsed[3].x).toBe(originalData[5].x);
+      expect(parsed[4].x).toBe(originalData[6].x);
     });
 
     it('should not crash with uneven points', function() {