fix(area_charts): correctly represent baseline with negative data poi…

…nts (#896)

This commit fixes the rendering issue when using negative values in area charts. The correct approach
is to draw the area with a zero baseline (or dummy 1 baseline for log y scale).

integration/tests/area_stories.test.ts

@@ -63,4 +63,32 @@ describe('Area series stories', () => {
       );
     });
   });
+  describe('Negative log Areas', () => {
+    it('snows negative values with log scale', async () => {
+      await common.expectChartAtUrlToMatchScreenshot(
+        'http://localhost:9001/?path=/story/area-chart--with-negative-values&knob-Y scale=log',
+      );
+    });
+    it('snows only positive domain mixed polarity domain', async () => {
+      await common.expectChartAtUrlToMatchScreenshot(
+        'http://localhost:9001/?path=/story/area-chart--with-negative-and-positive&knob-Y scale=log',
+      );
+    });
+
+    it('snows only positive values when hiding negative one', async () => {
+      const action = async () => await page.click('.echLegendItem:nth-child(2) .echLegendItem__label');
+      await common.expectChartAtUrlToMatchScreenshot(
+        'http://localhost:9001/?path=/story/area-chart--with-negative-and-positive&knob-Y scale=log',
+        { action },
+      );
+    });
+
+    it('snows only negative values when hiding positive one', async () => {
+      const action = async () => await page.click('.echLegendItem:nth-child(1) .echLegendItem__label');
+      await common.expectChartAtUrlToMatchScreenshot(
+        'http://localhost:9001/?path=/story/area-chart--with-negative-and-positive&knob-Y scale=log',
+        { action },
+      );
+    });
+  });
 });

src/chart_types/xy_chart/renderer/canvas/areas.ts

@@ -24,7 +24,7 @@ import { Rotation } from '../../../../utils/commons';
 import { Dimensions } from '../../../../utils/dimensions';
 import { AreaGeometry, PerPanel } from '../../../../utils/geometry';
 import { SharedGeometryStateStyle } from '../../../../utils/themes/theme';
-import { getGeometryStateStyle } from '../../rendering/rendering';
+import { getGeometryStateStyle } from '../../rendering/utils';
 import { renderPoints } from './points';
 import { renderLinePaths, renderAreaPath } from './primitives/path';
 import { buildAreaStyles } from './styles/area';

src/chart_types/xy_chart/renderer/canvas/bars.ts

@@ -24,7 +24,7 @@ import { Rotation } from '../../../../utils/commons';
 import { Dimensions } from '../../../../utils/dimensions';
 import { BarGeometry, PerPanel } from '../../../../utils/geometry';
 import { SharedGeometryStateStyle } from '../../../../utils/themes/theme';
-import { getGeometryStateStyle } from '../../rendering/rendering';
+import { getGeometryStateStyle } from '../../rendering/utils';
 import { renderRect } from './primitives/rect';
 import { buildBarStyles } from './styles/bar';
 import { withPanelTransform } from './utils/panel_transform';

src/chart_types/xy_chart/renderer/canvas/bubbles.ts

@@ -25,7 +25,7 @@ import { Rotation } from '../../../../utils/commons';
 import { Dimensions } from '../../../../utils/dimensions';
 import { BubbleGeometry, PerPanel, PointGeometry } from '../../../../utils/geometry';
 import { SharedGeometryStateStyle, GeometryStateStyle, PointStyle } from '../../../../utils/themes/theme';
-import { getGeometryStateStyle } from '../../rendering/rendering';
+import { getGeometryStateStyle } from '../../rendering/utils';
 import { renderPointGroup } from './points';
 
 interface BubbleGeometriesDataProps {

src/chart_types/xy_chart/renderer/canvas/lines.ts

@@ -24,7 +24,7 @@ import { Rotation } from '../../../../utils/commons';
 import { Dimensions } from '../../../../utils/dimensions';
 import { LineGeometry, PerPanel } from '../../../../utils/geometry';
 import { SharedGeometryStateStyle } from '../../../../utils/themes/theme';
-import { getGeometryStateStyle } from '../../rendering/rendering';
+import { getGeometryStateStyle } from '../../rendering/utils';
 import { renderPoints } from './points';
 import { renderLinePaths } from './primitives/path';
 import { buildLineStyles } from './styles/line';

src/chart_types/xy_chart/rendering/area.ts

@@ -0,0 +1,152 @@
+/*
+ * Licensed to Elasticsearch B.V. under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch B.V. licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+import { area } from 'd3-shape';
+
+import { Scale } from '../../../scales';
+import { Color } from '../../../utils/commons';
+import { CurveType, getCurveFactory } from '../../../utils/curves';
+import { Dimensions } from '../../../utils/dimensions';
+import { AreaGeometry } from '../../../utils/geometry';
+import { AreaSeriesStyle } from '../../../utils/themes/theme';
+import { IndexedGeometryMap } from '../utils/indexed_geometry_map';
+import { DataSeries, DataSeriesDatum } from '../utils/series';
+import { PointStyleAccessor } from '../utils/specs';
+import { renderPoints } from './points';
+import {
+  getClippedRanges,
+  getY0ScaledValueOrThrow,
+  getY1ScaledValueOrThrow,
+  isYValueDefined,
+  MarkSizeOptions,
+} from './utils';
+
+/** @internal */
+export function renderArea(
+  shift: number,
+  dataSeries: DataSeries,
+  xScale: Scale,
+  yScale: Scale,
+  panel: Dimensions,
+  color: Color,
+  curve: CurveType,
+  hasY0Accessors: boolean,
+  xScaleOffset: number,
+  seriesStyle: AreaSeriesStyle,
+  markSizeOptions: MarkSizeOptions,
+  isStacked = false,
+  pointStyleAccessor?: PointStyleAccessor,
+  hasFit?: boolean,
+): {
+  areaGeometry: AreaGeometry;
+  indexedGeometryMap: IndexedGeometryMap;
+} {
+  const y1Fn = getY1ScaledValueOrThrow(yScale);
+  const y0Fn = getY0ScaledValueOrThrow(yScale);
+  const definedFn = isYValueDefined(yScale, xScale);
+  const pathGenerator = area<DataSeriesDatum>()
+    .x(({ x }) => xScale.scaleOrThrow(x) - xScaleOffset)
+    .y1(y1Fn)
+    .y0(y0Fn)
+    .defined((datum) => {
+      return definedFn(datum) && (hasY0Accessors ? definedFn(datum, 'y0') : true);
+    })
+    .curve(getCurveFactory(curve));
+
+  const clippedRanges = getClippedRanges(dataSeries.data, xScale, xScaleOffset);
+
+  let y1Line: string | null;
+
+  try {
+    y1Line = pathGenerator.lineY1()(dataSeries.data);
+  } catch {
+    // When values are not scalable
+    y1Line = null;
+  }
+
+  const lines: string[] = [];
+  if (y1Line) {
+    lines.push(y1Line);
+  }
+  if (hasY0Accessors) {
+    let y0Line: string | null;
+
+    try {
+      y0Line = pathGenerator.lineY0()(dataSeries.data);
+    } catch {
+      // When values are not scalable
+      y0Line = null;
+    }
+    if (y0Line) {
+      lines.push(y0Line);
+    }
+  }
+
+  const { pointGeometries, indexedGeometryMap } = renderPoints(
+    shift - xScaleOffset,
+    dataSeries,
+    xScale,
+    yScale,
+    panel,
+    color,
+    seriesStyle.line,
+    hasY0Accessors,
+    markSizeOptions,
+    pointStyleAccessor,
+    false,
+  );
+
+  let areaPath: string;
+
+  try {
+    areaPath = pathGenerator(dataSeries.data) || '';
+  } catch {
+    // When values are not scalable
+    areaPath = '';
+  }
+
+  const areaGeometry: AreaGeometry = {
+    area: areaPath,
+    lines,
+    points: pointGeometries,
+    color,
+    transform: {
+      y: 0,
+      x: shift,
+    },
+    seriesIdentifier: {
+      key: dataSeries.key,
+      specId: dataSeries.specId,
+      yAccessor: dataSeries.yAccessor,
+      splitAccessors: dataSeries.splitAccessors,
+      seriesKeys: dataSeries.seriesKeys,
+      smHorizontalAccessorValue: dataSeries.smHorizontalAccessorValue,
+      smVerticalAccessorValue: dataSeries.smVerticalAccessorValue,
+    },
+    seriesAreaStyle: seriesStyle.area,
+    seriesAreaLineStyle: seriesStyle.line,
+    seriesPointStyle: seriesStyle.point,
+    isStacked,
+    clippedRanges,
+    hideClippedRanges: !hasFit,
+  };
+  return {
+    areaGeometry,
+    indexedGeometryMap,
+  };
+}