fix: adjust domain & range for single value histogram

src/lib/axes/axis_utils.ts

@@ -61,12 +61,23 @@ export function computeAxisTicksDimensions(
   chartRotation: Rotation,
   axisConfig: AxisConfig,
   barsPadding?: number,
+  enableHistogramMode?: boolean,
 ): AxisTicksDimensions | null {
   if (axisSpec.hide) {
     return null;
   }
 
-  const scale = getScaleForAxisSpec(axisSpec, xDomain, yDomain, totalBarsInCluster, chartRotation, 0, 1, barsPadding);
+  const scale = getScaleForAxisSpec(
+    axisSpec,
+    xDomain,
+    yDomain,
+    totalBarsInCluster,
+    chartRotation,
+    0,
+    1,
+    barsPadding,
+    enableHistogramMode,
+  );
   if (!scale) {
     throw new Error(`Cannot compute scale for axis spec ${axisSpec.id}`);
   }
@@ -112,6 +123,7 @@ export function getScaleForAxisSpec(
   minRange: number,
   maxRange: number,
   barsPadding?: number,
+  enableHistogramMode?: boolean,
 ): Scale | null {
   const axisIsYDomain = isYDomain(axisSpec.position, chartRotation);
 
@@ -122,7 +134,7 @@ export function getScaleForAxisSpec(
     }
     return null;
   } else {
-    return computeXScale(xDomain, totalBarsInCluster, minRange, maxRange, barsPadding);
+    return computeXScale(xDomain, totalBarsInCluster, minRange, maxRange, barsPadding, enableHistogramMode);
   }
 }
 
@@ -580,6 +592,7 @@ export function getAxisTicksPositions(
       minMaxRanges.minRange,
       minMaxRanges.maxRange,
       barsPadding,
+      enableHistogramMode,
     );
 
     if (!scale) {

src/lib/series/scales.test.ts

@@ -41,6 +41,44 @@ describe('Series scales', () => {
     expect(scale.scale(3)).toBe(expectedBandwidth * 0);
   });
 
+  describe('computeXScale with single value domain', () => {
+    const maxRange = 120;
+    const singleDomainValue = 3;
+    const minInterval = 1;
+
+    test('should return extended domain & range when in histogram mode', () => {
+      const xDomainSingleValue: XDomain = {
+        type: 'xDomain',
+        isBandScale: true,
+        domain: [singleDomainValue, singleDomainValue],
+        minInterval: minInterval,
+        scaleType: ScaleType.Linear,
+      };
+      const enableHistogramMode = true;
+
+      const scale = computeXScale(xDomainSingleValue, 1, 0, maxRange, 0, enableHistogramMode);
+      expect(scale.bandwidth).toBe(maxRange);
+      expect(scale.domain).toEqual([singleDomainValue, singleDomainValue + minInterval]);
+      expect(scale.range).toEqual([0, maxRange]);
+    });
+
+    test('should return unextended domain & range when not in histogram mode', () => {
+      const xDomainSingleValue: XDomain = {
+        type: 'xDomain',
+        isBandScale: true,
+        domain: [singleDomainValue, singleDomainValue],
+        minInterval: minInterval,
+        scaleType: ScaleType.Linear,
+      };
+      const enableHistogramMode = false;
+
+      const scale = computeXScale(xDomainSingleValue, 1, 0, maxRange, 0, enableHistogramMode);
+      expect(scale.bandwidth).toBe(maxRange);
+      expect(scale.domain).toEqual([singleDomainValue, singleDomainValue]);
+      expect(scale.range).toEqual([0, 0]);
+    });
+  });
+
   test('should compute X Scale ordinal', () => {
     const nonZeroGroupScale = computeXScale(xDomainOrdinal, 1, 120, 0);
     const expectedBandwidth = 60;

src/lib/series/scales.ts

@@ -50,6 +50,7 @@ export function computeXScale(
   minRange: number,
   maxRange: number,
   barsPadding?: number,
+  enableHistogramMode?: boolean,
 ): Scale {
   const { scaleType, minInterval, domain, isBandScale, timeZone } = xDomain;
   const rangeDiff = Math.abs(maxRange - minRange);
@@ -60,20 +61,32 @@ export function computeXScale(
     return new ScaleBand(domain, [minRange, maxRange], bandwidth, barsPadding);
   } else {
     if (isBandScale) {
-      const intervalCount = (domain[1] - domain[0]) / minInterval;
-      const bandwidth = rangeDiff / (intervalCount + 1);
-      const start = isInverse ? minRange - bandwidth : minRange;
-      const end = isInverse ? maxRange : maxRange - bandwidth;
-      return new ScaleContinuous(
+      const [domainMin, domainMax] = domain;
+      const isSingleValueHistogram = enableHistogramMode && domainMax - domainMin === 0;
+
+      const adjustedDomainMax = isSingleValueHistogram ? domainMin + minInterval : domainMax;
+      const adjustedDomain = [domainMin, adjustedDomainMax];
+
+      const intervalCount = (adjustedDomain[1] - adjustedDomain[0]) / minInterval;
+      const intervalCountOffest = isSingleValueHistogram ? 0 : 1;
+      const bandwidth = rangeDiff / (intervalCount + intervalCountOffest);
+
+      const rangeEndOffset = isSingleValueHistogram ? 0 : bandwidth;
+      const start = isInverse ? minRange - rangeEndOffset : minRange;
+      const end = isInverse ? maxRange : maxRange - rangeEndOffset;
+
+      const scale = new ScaleContinuous(
         scaleType,
-        domain,
+        adjustedDomain,
         [start, end],
         bandwidth / totalBarsInCluster,
         minInterval,
         timeZone,
         totalBarsInCluster,
         barsPadding,
       );
+
+      return scale;
     } else {
       return new ScaleContinuous(
         scaleType,

src/state/chart_state.ts

@@ -836,6 +836,7 @@ export class ChartStore {
         this.chartRotation,
         this.chartTheme.axes,
         barsPadding,
+        this.enableHistogramMode.get(),
       );
       if (dimensions) {
         this.axesTicksDimensions.set(id, dimensions);

src/state/utils.ts

@@ -193,7 +193,7 @@ export function computeSeriesGeometries(
   const { stackedBarsInCluster, totalBarsInCluster } = countBarsInCluster(stacked, nonStacked);
 
   // compute scales
-  const xScale = computeXScale(xDomain, totalBarsInCluster, 0, width, barsPadding);
+  const xScale = computeXScale(xDomain, totalBarsInCluster, 0, width, barsPadding, enableHistogramMode);
   const yScales = computeYScales(yDomain, height, 0);
 
   // compute colors

stories/annotations.tsx

@@ -547,4 +547,64 @@ storiesOf('Annotations', module)
         />
       </Chart>
     );
+  })
+  .add('[test] line annotation single value histogram', () => {
+    const dataValues = [
+      {
+        dataValue: 3.5,
+      },
+    ];
+
+    const style = {
+      line: {
+        strokeWidth: 3,
+        stroke: '#f00',
+        opacity: 1,
+      },
+      details: {
+        fontSize: 12,
+        fontFamily: 'Arial',
+        fontStyle: 'bold',
+        fill: 'gray',
+        padding: 0,
+      },
+    };
+
+    const chartRotation = select<Rotation>(
+      'chartRotation',
+      {
+        '0 deg': 0,
+        '90 deg': 90,
+        '-90 deg': -90,
+        '180 deg': 180,
+      },
+      0,
+    );
+
+    const xDomain = {
+      minInterval: 1,
+    };
+
+    return (
+      <Chart className={'story-chart'}>
+        <Settings debug={boolean('debug', false)} rotation={chartRotation} xDomain={xDomain} />
+        <LineAnnotation
+          annotationId={getAnnotationId('anno_1')}
+          domainType={AnnotationDomainTypes.XDomain}
+          dataValues={dataValues}
+          style={style}
+        />
+        <Axis id={getAxisId('horizontal')} position={Position.Bottom} title={'x-domain axis'} />
+        <Axis id={getAxisId('vertical')} title={'y-domain axis'} position={Position.Left} />
+        <BarSeries
+          enableHistogramMode={true}
+          id={getSpecId('bars')}
+          xScaleType={ScaleType.Linear}
+          yScaleType={ScaleType.Linear}
+          xAccessor="x"
+          yAccessors={['y']}
+          data={[{ x: 3, y: 2 }]}
+        />
+      </Chart>
+    );
   });