[grafana/UI] Hoovering over a legend label highlights the corresponding pie slice (#32941)

* Hoovering over a legend label hightlighs that pie slice

* Change to event bus

* Adds EventBusWithSource to help identify the origin of the event

* Add tests and fix bug with incorrect source

* Clean up PieChart and EventBus a bit

* Fix bug when payload.source is undefined

* Add some documentation and adjust naming

* useState instead of useSetState

* Clean up some more documentation

* Move eventbus to state

* add event bus actions to the debug panel

* add event bus actions to the debug panel

* Try to make the naming a bit clearer

* Try passing eventbus as context

* Fix lint issues

* Move event bus context to panel chrome

* Fix event handler functions

* switch to using useCallback for legend item callbacks

* Remove unused parameters

* Add id to panel fixture of PanelChrome test

* Simplify event source

* Place eventBus inside more generic context

* Push handling of context up the tree to VizLegend

only export usePanelContext and PanelContextProvider

implement isOwnEvent on EventBus

some cleanup

Co-authored-by: Ryan McKinley <ryantxu@gmail.com>
Co-authored-by: Dominik Prokop <dominik.prokop@grafana.com>

packages/grafana-data/src/events/EventBus.test.ts

@@ -1,6 +1,7 @@
-import { EventBusSrv } from './EventBus';
-import { BusEventWithPayload } from './types';
+import { EventBusSrv, EventBusWithSource } from './EventBus';
+import { BusEvent, BusEventWithPayload } from './types';
 import { eventFactory } from './eventFactory';
+import { DataHoverEvent } from './common';
 
 interface LoginEventPayload {
   logins: number;
@@ -46,6 +47,27 @@ describe('EventBus', () => {
     expect(events.length).toBe(1);
   });
 
+  describe('EventBusWithSource', () => {
+    it('can add sources to the source path', () => {
+      const bus = new EventBusSrv();
+      const busWithSource = new EventBusWithSource(bus, 'foo');
+      expect(busWithSource.source).toEqual('foo');
+    });
+
+    it('adds the source to the event payload', () => {
+      const bus = new EventBusSrv();
+      let events: BusEvent[] = [];
+
+      bus.subscribe(DataHoverEvent, (event) => events.push(event));
+
+      const busWithSource = new EventBusWithSource(bus, 'foo');
+      busWithSource.publish({ type: DataHoverEvent.type });
+
+      expect(events.length).toEqual(1);
+      expect(events[0].payload.source).toEqual('foo');
+    });
+  });
+
   describe('Legacy emitter behavior', () => {
     it('Supports legacy events', () => {
       const bus = new EventBusSrv();

packages/grafana-data/src/events/EventBus.ts

@@ -1,5 +1,6 @@
 import EventEmitter from 'eventemitter3';
 import { Unsubscribable, Observable } from 'rxjs';
+import { PayloadWithSource } from './common';
 import {
   EventBus,
   LegacyEmitter,
@@ -8,6 +9,7 @@ import {
   LegacyEventHandler,
   BusEvent,
   AppEvent,
+  BusEventWithPayload,
 } from './types';
 
 /**
@@ -90,3 +92,42 @@ export class EventBusSrv implements EventBus, LegacyEmitter {
     this.emitter.removeAllListeners();
   }
 }
+
+/**
+ * @alpha
+ *
+ * Wraps EventBus and adds a source to help with identifying if a subscriber should react to the event or not.
+ */
+export class EventBusWithSource implements EventBus {
+  source: string;
+  eventBus: EventBus;
+
+  constructor(eventBus: EventBus, source: string) {
+    this.eventBus = eventBus;
+    this.source = source;
+  }
+
+  publish<T extends BusEvent>(event: T): void {
+    const decoratedEvent = {
+      ...event,
+      ...{ payload: { ...event.payload, ...{ source: this.source } } },
+    };
+    this.eventBus.publish(decoratedEvent);
+  }
+
+  subscribe<T extends BusEvent>(eventType: BusEventType<T>, handler: BusEventHandler<T>): Unsubscribable {
+    return this.eventBus.subscribe(eventType, handler);
+  }
+
+  getStream<T extends BusEvent>(eventType: BusEventType<T>): Observable<T> {
+    return this.eventBus.getStream(eventType);
+  }
+
+  removeAllListeners(): void {
+    this.eventBus.removeAllListeners();
+  }
+
+  isOwnEvent(event: BusEventWithPayload<PayloadWithSource>): boolean {
+    return event.payload.source === this.source;
+  }
+}

packages/grafana-data/src/events/common.ts

@@ -0,0 +1,38 @@
+import { DataFrame } from '../types';
+import { BusEventWithPayload } from './types';
+
+/** @alpha */
+export interface PayloadWithSource {
+  source?: string; // source from where the event originates
+}
+
+/** @alpha */
+export interface DataHoverPayload extends PayloadWithSource {
+  raw: any; // Original mouse event (includes pageX etc)
+
+  x: Record<string, any>; // { time: 5678 },
+  y: Record<string, any>; // { __fixed: 123, lengthft: 456 }  // each axis|scale gets a value
+
+  data?: DataFrame; // source data
+  rowIndex?: number; // the hover row
+  columnIndex?: number; // the hover column
+  dataId?: string; // identifying string to correlate data between publishers and subscribers
+
+  // When dragging, this will capture the original state
+  down?: Omit<DataHoverPayload, 'down'>;
+}
+
+/** @alpha */
+export class DataHoverEvent extends BusEventWithPayload<DataHoverPayload> {
+  static type = 'data-hover';
+}
+
+/** @alpha */
+export class DataHoverClearEvent extends BusEventWithPayload<DataHoverPayload> {
+  static type = 'data-hover-clear';
+}
+
+/** @alpha */
+export class DataSelectEvent extends BusEventWithPayload<DataHoverPayload> {
+  static type = 'data-select';
+}

packages/grafana-data/src/events/index.ts

@@ -1,3 +1,4 @@
 export * from './eventFactory';
 export * from './types';
 export * from './EventBus';
+export * from './common';

packages/grafana-ui/src/components/PanelChrome/PanelContext.ts

@@ -0,0 +1,18 @@
+import { EventBusWithSource } from '@grafana/data';
+import React from 'react';
+
+interface PanelContext {
+  eventBus?: EventBusWithSource;
+}
+
+const PanelContextRoot = React.createContext<PanelContext>({});
+
+/**
+ * @alpha
+ */
+export const PanelContextProvider = PanelContextRoot.Provider;
+
+/**
+ * @alpha
+ */
+export const usePanelContext = () => React.useContext(PanelContextRoot);

packages/grafana-ui/src/components/PanelChrome/index.ts

@@ -36,3 +36,5 @@ export {
   ErrorIndicator as PanelChromeErrorIndicator,
   ErrorIndicatorProps as PanelChromeErrorIndicatorProps,
 } from './ErrorIndicator';
+
+export { usePanelContext, PanelContextProvider } from './PanelContext';

packages/grafana-ui/src/components/PieChart/PieChart.tsx

@@ -1,5 +1,7 @@
-import React, { FC, ReactNode } from 'react';
+import React, { FC, ReactNode, useState } from 'react';
 import {
+  DataHoverClearEvent,
+  DataHoverEvent,
   FALLBACK_COLOR,
   FieldDisplay,
   formattedValueToString,
@@ -30,6 +32,7 @@ import {
 } from './types';
 import { getTooltipContainerStyles } from '../../themes/mixins';
 import { SeriesTable, SeriesTableRowProps, VizTooltipOptions } from '../VizTooltip';
+import { usePanelContext } from '../PanelChrome';
 
 const defaultLegendOptions: PieChartLegendOptions = {
   displayMode: LegendDisplayMode.List,
@@ -38,6 +41,9 @@ const defaultLegendOptions: PieChartLegendOptions = {
   values: [PieChartLegendValues.Percent],
 };
 
+/**
+ * @beta
+ */
 export const PieChart: FC<PieChartProps> = ({
   data,
   timeZone,
@@ -52,6 +58,25 @@ export const PieChart: FC<PieChartProps> = ({
   ...restProps
 }) => {
   const theme = useTheme();
+  const [highlightedTitle, setHighlightedTitle] = useState<string>();
+  const { eventBus } = usePanelContext();
+
+  if (eventBus) {
+    const setHighlightedSlice = (event: DataHoverEvent) => {
+      if (eventBus.isOwnEvent(event)) {
+        setHighlightedTitle(event.payload.dataId);
+      }
+    };
+
+    const resetHighlightedSlice = (event: DataHoverClearEvent) => {
+      if (eventBus.isOwnEvent(event)) {
+        setHighlightedTitle(undefined);
+      }
+    };
+
+    eventBus.subscribe(DataHoverEvent, setHighlightedSlice);
+    eventBus.subscribe(DataHoverClearEvent, resetHighlightedSlice);
+  }
 
   const getLegend = (fields: FieldDisplay[], legendOptions: PieChartLegendOptions) => {
     if (legendOptions.displayMode === LegendDisplayMode.Hidden) {
@@ -117,6 +142,7 @@ export const PieChart: FC<PieChartProps> = ({
           <PieChartSvg
             width={vizWidth}
             height={vizHeight}
+            highlightedTitle={highlightedTitle}
             fieldDisplayValues={fieldDisplayValues}
             tooltipOptions={tooltipOptions}
             {...restProps}
@@ -132,6 +158,7 @@ export const PieChartSvg: FC<PieChartSvgProps> = ({
   pieType,
   width,
   height,
+  highlightedTitle,
   useGradients = true,
   displayLabels = [],
   tooltipOptions,
@@ -194,6 +221,7 @@ export const PieChartSvg: FC<PieChartSvgProps> = ({
             {(pie) => {
               return pie.arcs.map((arc) => {
                 const color = arc.data.display.color ?? FALLBACK_COLOR;
+                const highlighted = highlightedTitle === arc.data.display.title;
                 const label = showLabel ? (
                   <PieLabel
                     arc={arc}
@@ -210,6 +238,7 @@ export const PieChartSvg: FC<PieChartSvgProps> = ({
                       {(api) => (
                         <PieSlice
                           tooltip={tooltip}
+                          highlighted={highlighted}
                           arc={arc}
                           pie={pie}
                           fill={getGradientColor(color)}
@@ -225,6 +254,7 @@ export const PieChartSvg: FC<PieChartSvgProps> = ({
                   return (
                     <PieSlice
                       key={arc.index}
+                      highlighted={highlighted}
                       tooltip={tooltip}
                       arc={arc}
                       pie={pie}
@@ -260,11 +290,12 @@ const PieSlice: FC<{
   children: ReactNode;
   arc: PieArcDatum<FieldDisplay>;
   pie: ProvidedProps<FieldDisplay>;
+  highlighted?: boolean;
   fill: string;
   tooltip: UseTooltipParams<SeriesTableRowProps[]>;
   tooltipOptions: VizTooltipOptions;
   openMenu?: (event: React.MouseEvent<SVGElement>) => void;
-}> = ({ arc, children, pie, openMenu, fill, tooltip, tooltipOptions }) => {
+}> = ({ arc, children, pie, highlighted, openMenu, fill, tooltip, tooltipOptions }) => {
   const theme = useTheme();
   const styles = useStyles(getStyles);
 
@@ -280,7 +311,7 @@ const PieSlice: FC<{
   return (
     <g
       key={arc.data.display.title}
-      className={styles.svgArg}
+      className={highlighted ? styles.svgArg.highlighted : styles.svgArg.normal}
       onMouseMove={tooltipOptions.mode !== 'none' ? onMouseMoveOverArc : undefined}
       onMouseOut={tooltip.hideTooltip}
       onClick={openMenu}
@@ -420,12 +451,18 @@ const getStyles = (theme: GrafanaTheme) => {
       align-items: center;
       justify-content: center;
     `,
-    svgArg: css`
-      transition: all 200ms ease-in-out;
-      &:hover {
+    svgArg: {
+      normal: css`
+        transition: all 200ms ease-in-out;
+        &:hover {
+          transform: scale3d(1.03, 1.03, 1);
+        }
+      `,
+      highlighted: css`
+        transition: all 200ms ease-in-out;
         transform: scale3d(1.03, 1.03, 1);
-      }
-    `,
+      `,
+    },
     tooltipPortal: css`
       ${getTooltipContainerStyles(theme)}
     `,

packages/grafana-ui/src/components/PieChart/types.ts

@@ -2,18 +2,31 @@ import { DataFrame, FieldConfigSource, FieldDisplay, InterpolateFunction, Reduce
 import { VizTooltipOptions } from '../VizTooltip';
 import { VizLegendOptions } from '..';
 
+/**
+ * @beta
+ */
 export interface PieChartSvgProps {
   height: number;
   width: number;
   fieldDisplayValues: FieldDisplay[];
   pieType: PieChartType;
+  highlightedTitle?: string;
   displayLabels?: PieChartLabels[];
   useGradients?: boolean;
   onSeriesColorChange?: (label: string, color: string) => void;
   tooltipOptions: VizTooltipOptions;
 }
 
-export interface PieChartProps extends Omit<PieChartSvgProps, 'fieldDisplayValues'> {
+/**
+ * @beta
+ */
+export interface PieChartProps {
+  height: number;
+  width: number;
+  pieType: PieChartType;
+  displayLabels?: PieChartLabels[];
+  useGradients?: boolean;
+  onSeriesColorChange?: (label: string, color: string) => void;
   legendOptions?: PieChartLegendOptions;
   tooltipOptions: VizTooltipOptions;
   reduceOptions: ReduceDataOptions;
@@ -23,22 +36,34 @@ export interface PieChartProps extends Omit<PieChartSvgProps, 'fieldDisplayValue
   timeZone?: string;
 }
 
+/**
+ * @beta
+ */
 export enum PieChartType {
   Pie = 'pie',
   Donut = 'donut',
 }
 
+/**
+ * @beta
+ */
 export enum PieChartLegendValues {
   Value = 'value',
   Percent = 'percent',
 }
 
+/**
+ * @beta
+ */
 export enum PieChartLabels {
   Name = 'name',
   Value = 'value',
   Percent = 'percent',
 }
 
+/**
+ * @beta
+ */
 export interface PieChartLegendOptions extends VizLegendOptions {
   values: PieChartLegendValues[];
 }

packages/grafana-ui/src/components/VizLegend/VizLegend.tsx

@@ -1,8 +1,10 @@
-import React from 'react';
-import { LegendProps } from './types';
+import React, { useCallback } from 'react';
+import { LegendProps, VizLegendItem } from './types';
 import { LegendDisplayMode } from './models.gen';
 import { VizLegendTable } from './VizLegendTable';
 import { VizLegendList } from './VizLegendList';
+import { DataHoverClearEvent, DataHoverEvent } from '@grafana/data';
+import { usePanelContext } from '../PanelChrome';
 
 /**
  * @public
@@ -18,6 +20,38 @@ export const VizLegend: React.FunctionComponent<LegendProps> = ({
   placement,
   className,
 }) => {
+  const { eventBus } = usePanelContext();
+
+  const onMouseEnter = useCallback(
+    (item: VizLegendItem, event: React.MouseEvent<HTMLElement, MouseEvent>) => {
+      eventBus?.publish({
+        type: DataHoverEvent.type,
+        payload: {
+          raw: event,
+          x: 0,
+          y: 0,
+          dataId: item.label,
+        },
+      });
+    },
+    [eventBus]
+  );
+
+  const onMouseOut = useCallback(
+    (item: VizLegendItem, event: React.MouseEvent<HTMLElement, MouseEvent>) => {
+      eventBus?.publish({
+        type: DataHoverClearEvent.type,
+        payload: {
+          raw: event,
+          x: 0,
+          y: 0,
+          dataId: item.label,
+        },
+      });
+    },
+    [eventBus]
+  );
+
   switch (displayMode) {
     case LegendDisplayMode.Table:
       return (
@@ -29,6 +63,8 @@ export const VizLegend: React.FunctionComponent<LegendProps> = ({
           sortDesc={sortDesc}
           onLabelClick={onLabelClick}
           onToggleSort={onToggleSort}
+          onLabelMouseEnter={onMouseEnter}
+          onLabelMouseOut={onMouseOut}
           onSeriesColorChange={onSeriesColorChange}
         />
       );
@@ -38,6 +74,8 @@ export const VizLegend: React.FunctionComponent<LegendProps> = ({
           className={className}
           items={items}
           placement={placement}
+          onLabelMouseEnter={onMouseEnter}
+          onLabelMouseOut={onMouseOut}
           onLabelClick={onLabelClick}
           onSeriesColorChange={onSeriesColorChange}
         />

packages/grafana-ui/src/components/VizLegend/VizLegendList.tsx

@@ -17,6 +17,8 @@ export const VizLegendList: React.FunctionComponent<Props> = ({
   itemRenderer,
   onSeriesColorChange,
   onLabelClick,
+  onLabelMouseEnter,
+  onLabelMouseOut,
   placement,
   className,
 }) => {
@@ -25,7 +27,13 @@ export const VizLegendList: React.FunctionComponent<Props> = ({
   if (!itemRenderer) {
     /* eslint-disable-next-line react/display-name */
     itemRenderer = (item) => (
-      <VizLegendListItem item={item} onLabelClick={onLabelClick} onSeriesColorChange={onSeriesColorChange} />
+      <VizLegendListItem
+        item={item}
+        onLabelClick={onLabelClick}
+        onSeriesColorChange={onSeriesColorChange}
+        onLabelMouseEnter={onLabelMouseEnter}
+        onLabelMouseOut={onLabelMouseOut}
+      />
     );
   }
 

packages/grafana-ui/src/components/VizLegend/VizLegendListItem.tsx

@@ -1,4 +1,4 @@
-import React from 'react';
+import React, { useCallback } from 'react';
 import { css, cx } from '@emotion/css';
 import { VizLegendSeriesIcon } from './VizLegendSeriesIcon';
 import { VizLegendItem, SeriesColorChangeHandler } from './types';
@@ -11,31 +11,65 @@ export interface Props {
   className?: string;
   onLabelClick?: (item: VizLegendItem, event: React.MouseEvent<HTMLDivElement>) => void;
   onSeriesColorChange?: SeriesColorChangeHandler;
+  onLabelMouseEnter?: (item: VizLegendItem, event: React.MouseEvent<HTMLDivElement>) => void;
+  onLabelMouseOut?: (item: VizLegendItem, event: React.MouseEvent<HTMLDivElement>) => void;
 }
 
 /**
  * @internal
  */
-export const VizLegendListItem: React.FunctionComponent<Props> = ({ item, onSeriesColorChange, onLabelClick }) => {
+export const VizLegendListItem: React.FunctionComponent<Props> = ({
+  item,
+  onSeriesColorChange,
+  onLabelClick,
+  onLabelMouseEnter,
+  onLabelMouseOut,
+}) => {
   const styles = useStyles(getStyles);
 
+  const onMouseEnter = useCallback(
+    (event: React.MouseEvent<HTMLDivElement, MouseEvent>) => {
+      if (onLabelMouseEnter) {
+        onLabelMouseEnter(item, event);
+      }
+    },
+    [item, onLabelMouseEnter]
+  );
+
+  const onMouseOut = useCallback(
+    (event: React.MouseEvent<HTMLDivElement, MouseEvent>) => {
+      if (onLabelMouseOut) {
+        onLabelMouseOut(item, event);
+      }
+    },
+    [item, onLabelMouseOut]
+  );
+
+  const onClick = useCallback(
+    (event: React.MouseEvent<HTMLDivElement, MouseEvent>) => {
+      if (onLabelClick) {
+        onLabelClick(item, event);
+      }
+    },
+    [item, onLabelClick]
+  );
+
+  const onColorChange = useCallback(
+    (color: string) => {
+      if (onSeriesColorChange) {
+        onSeriesColorChange(item.label, color);
+      }
+    },
+    [item, onSeriesColorChange]
+  );
+
   return (
     <div className={styles.itemWrapper}>
-      <VizLegendSeriesIcon
-        disabled={!onSeriesColorChange}
-        color={item.color}
-        onColorChange={(color) => {
-          if (onSeriesColorChange) {
-            onSeriesColorChange(item.label, color);
-          }
-        }}
-      />
+      <VizLegendSeriesIcon disabled={!onSeriesColorChange} color={item.color} onColorChange={onColorChange} />
       <div
-        onClick={(event) => {
-          if (onLabelClick) {
-            onLabelClick(item, event);
-          }
-        }}
+        onMouseEnter={onMouseEnter}
+        onMouseOut={onMouseOut}
+        onClick={onClick}
         className={cx(styles.label, item.disabled && styles.labelDisabled)}
       >
         {item.label}

packages/grafana-ui/src/components/VizLegend/VizLegendTable.tsx

@@ -18,6 +18,8 @@ export const VizLegendTable: FC<VizLegendTableProps> = ({
   className,
   onToggleSort,
   onLabelClick,
+  onLabelMouseEnter,
+  onLabelMouseOut,
   onSeriesColorChange,
 }) => {
   const styles = useStyles(getStyles);
@@ -57,6 +59,8 @@ export const VizLegendTable: FC<VizLegendTableProps> = ({
         item={item}
         onSeriesColorChange={onSeriesColorChange}
         onLabelClick={onLabelClick}
+        onLabelMouseEnter={onLabelMouseEnter}
+        onLabelMouseOut={onLabelMouseOut}
       />
     );
   }

packages/grafana-ui/src/components/VizLegend/VizLegendTableItem.tsx

@@ -1,4 +1,4 @@
-import React from 'react';
+import React, { useCallback } from 'react';
 import { css, cx } from '@emotion/css';
 import { VizLegendSeriesIcon } from './VizLegendSeriesIcon';
 import { VizLegendItem, SeriesColorChangeHandler } from './types';
@@ -12,6 +12,8 @@ export interface Props {
   className?: string;
   onLabelClick?: (item: VizLegendItem, event: React.MouseEvent<HTMLDivElement>) => void;
   onSeriesColorChange?: SeriesColorChangeHandler;
+  onLabelMouseEnter?: (item: VizLegendItem, event: React.MouseEvent<HTMLDivElement>) => void;
+  onLabelMouseOut?: (item: VizLegendItem, event: React.MouseEvent<HTMLDivElement>) => void;
 }
 
 /**
@@ -21,29 +23,57 @@ export const LegendTableItem: React.FunctionComponent<Props> = ({
   item,
   onSeriesColorChange,
   onLabelClick,
+  onLabelMouseEnter,
+  onLabelMouseOut,
   className,
 }) => {
   const styles = useStyles(getStyles);
 
+  const onMouseEnter = useCallback(
+    (event: React.MouseEvent<HTMLDivElement, MouseEvent>) => {
+      if (onLabelMouseEnter) {
+        onLabelMouseEnter(item, event);
+      }
+    },
+    [item, onLabelMouseEnter]
+  );
+
+  const onMouseOut = useCallback(
+    (event: React.MouseEvent<HTMLDivElement, MouseEvent>) => {
+      if (onLabelMouseOut) {
+        onLabelMouseOut(item, event);
+      }
+    },
+    [item, onLabelMouseOut]
+  );
+
+  const onClick = useCallback(
+    (event: React.MouseEvent<HTMLDivElement, MouseEvent>) => {
+      if (onLabelClick) {
+        onLabelClick(item, event);
+      }
+    },
+    [item, onLabelClick]
+  );
+
+  const onColorChange = useCallback(
+    (color: string) => {
+      if (onSeriesColorChange) {
+        onSeriesColorChange(item.label, color);
+      }
+    },
+    [item, onSeriesColorChange]
+  );
+
   return (
     <tr className={cx(styles.row, className)}>
       <td>
         <span className={styles.itemWrapper}>
-          <VizLegendSeriesIcon
-            disabled={!onSeriesColorChange}
-            color={item.color}
-            onColorChange={(color) => {
-              if (onSeriesColorChange) {
-                onSeriesColorChange(item.label, color);
-              }
-            }}
-          />
+          <VizLegendSeriesIcon disabled={!onSeriesColorChange} color={item.color} onColorChange={onColorChange} />
           <div
-            onClick={(event) => {
-              if (onLabelClick) {
-                onLabelClick(item, event);
-              }
-            }}
+            onMouseEnter={onMouseEnter}
+            onMouseOut={onMouseOut}
+            onClick={onClick}
             className={cx(styles.label, item.disabled && styles.labelDisabled)}
           >
             {item.label} {item.yAxis === 2 && <span className={styles.yAxisLabel}>(right y-axis)</span>}

packages/grafana-ui/src/components/VizLegend/types.ts

@@ -1,4 +1,5 @@
 import { DataFrameFieldIndex, DisplayValue } from '@grafana/data';
+import React from 'react';
 import { LegendDisplayMode, LegendPlacement } from './models.gen';
 
 export interface VizLegendBaseProps {
@@ -8,6 +9,8 @@ export interface VizLegendBaseProps {
   itemRenderer?: (item: VizLegendItem, index: number) => JSX.Element;
   onSeriesColorChange?: SeriesColorChangeHandler;
   onLabelClick?: (item: VizLegendItem, event: React.MouseEvent<HTMLElement>) => void;
+  onLabelMouseEnter?: (item: VizLegendItem, event: React.MouseEvent<HTMLElement>) => void;
+  onLabelMouseOut?: (item: VizLegendItem, event: React.MouseEvent<HTMLElement>) => void;
 }
 
 export interface VizLegendTableProps extends VizLegendBaseProps {

packages/grafana-ui/src/components/index.ts

@@ -94,6 +94,8 @@ export {
   PanelChromeLoadingIndicatorProps,
   PanelChromeErrorIndicator,
   PanelChromeErrorIndicatorProps,
+  PanelContextProvider,
+  usePanelContext,
 } from './PanelChrome';
 export { VizLayout, VizLayoutComponentType, VizLayoutLegendProps, VizLayoutProps } from './VizLayout/VizLayout';
 export { VizLegendItem } from './VizLegend/types';

public/app/features/dashboard/dashgrid/PanelChrome.test.tsx

@@ -32,6 +32,7 @@ function setupTestContext(options: Partial<Props>) {
   setTimeSrv(timeSrv);
   const defaults: Props = {
     panel: ({
+      id: 123,
       hasTitle: jest.fn(),
       replaceVariables: jest.fn(),
       events: { subscribe: jest.fn() },

public/app/features/dashboard/dashgrid/PanelChrome.tsx

@@ -4,7 +4,7 @@ import classNames from 'classnames';
 import { Subscription } from 'rxjs';
 // Components
 import { PanelHeader } from './PanelHeader/PanelHeader';
-import { ErrorBoundary } from '@grafana/ui';
+import { ErrorBoundary, PanelContextProvider } from '@grafana/ui';
 // Utils & Services
 import { getTimeSrv, TimeSrv } from '../services/TimeSrv';
 import { applyPanelTimeOverrides } from 'app/features/dashboard/utils/panel';
@@ -15,6 +15,7 @@ import { DashboardModel, PanelModel } from '../state';
 import { PANEL_BORDER } from 'app/core/constants';
 import {
   AbsoluteTimeRange,
+  EventBusWithSource,
   FieldConfigSource,
   getDefaultTimeRange,
   LoadingState,
@@ -46,6 +47,7 @@ export interface State {
   renderCounter: number;
   errorMessage?: string;
   refreshWhenInView: boolean;
+  eventBus: EventBusWithSource;
   data: PanelData;
 }
 
@@ -60,6 +62,7 @@ export class PanelChrome extends Component<Props, State> {
       isFirstLoad: true,
       renderCounter: 0,
       refreshWhenInView: false,
+      eventBus: new EventBusWithSource(props.dashboard.events, `panel-${props.panel.id}`),
       data: {
         state: LoadingState.NotStarted,
         series: [],
@@ -286,24 +289,26 @@ export class PanelChrome extends Component<Props, State> {
     return (
       <>
         <div className={panelContentClassNames}>
-          <PanelComponent
-            id={panel.id}
-            data={data}
-            title={panel.title}
-            timeRange={timeRange}
-            timeZone={this.props.dashboard.getTimezone()}
-            options={panelOptions}
-            fieldConfig={panel.fieldConfig}
-            transparent={panel.transparent}
-            width={panelWidth}
-            height={innerPanelHeight}
-            renderCounter={renderCounter}
-            replaceVariables={panel.replaceVariables}
-            onOptionsChange={this.onOptionsChange}
-            onFieldConfigChange={this.onFieldConfigChange}
-            onChangeTimeRange={this.onChangeTimeRange}
-            eventBus={dashboard.events}
-          />
+          <PanelContextProvider value={{ eventBus: this.state.eventBus }}>
+            <PanelComponent
+              id={panel.id}
+              data={data}
+              title={panel.title}
+              timeRange={timeRange}
+              timeZone={this.props.dashboard.getTimezone()}
+              options={panelOptions}
+              fieldConfig={panel.fieldConfig}
+              transparent={panel.transparent}
+              width={panelWidth}
+              height={innerPanelHeight}
+              renderCounter={renderCounter}
+              replaceVariables={panel.replaceVariables}
+              onOptionsChange={this.onOptionsChange}
+              onFieldConfigChange={this.onFieldConfigChange}
+              onChangeTimeRange={this.onChangeTimeRange}
+              eventBus={dashboard.events}
+            />
+          </PanelContextProvider>
         </div>
       </>
     );

public/app/plugins/panel/debug/DebugPanel.tsx

@@ -1,8 +1,9 @@
 import React, { Component } from 'react';
-import { fieldReducers, getFieldDisplayName, getFrameDisplayName, PanelProps, ReducerID } from '@grafana/data';
+import { PanelProps } from '@grafana/data';
 
-import { DebugPanelOptions, UpdateCounters, UpdateConfig } from './types';
-import { IconButton } from '@grafana/ui';
+import { DebugPanelOptions, DebugMode, UpdateCounters } from './types';
+import { EventBusLoggerPanel } from './EventBusLogger';
+import { RenderInfoViewer } from './RenderInfoViewer';
 
 type Props = PanelProps<DebugPanelOptions>;
 
@@ -40,57 +41,11 @@ export class DebugPanel extends Component<Props> {
   };
 
   render() {
-    const { data, options } = this.props;
-    const showCounters = options.counters ?? ({} as UpdateConfig);
-    this.counters.render++;
-    const now = Date.now();
-    const elapsed = now - this.lastRender;
-    this.lastRender = now;
+    const { options } = this.props;
+    if (options.mode === DebugMode.Events) {
+      return <EventBusLoggerPanel eventBus={this.props.eventBus} />;
+    }
 
-    const reducer = fieldReducers.get(ReducerID.lastNotNull);
-
-    return (
-      <div>
-        <div>
-          <IconButton name="step-backward" title="reset counters" onClick={this.resetCounters} />
-          <span>
-            {showCounters.render && <span>Render: {this.counters.render}&nbsp;</span>}
-            {showCounters.dataChanged && <span>Data: {this.counters.dataChanged}&nbsp;</span>}
-            {showCounters.schemaChanged && <span>Schema: {this.counters.schemaChanged}&nbsp;</span>}
-            <span>TIME: {elapsed}ms</span>
-          </span>
-        </div>
-
-        {data.series &&
-          data.series.map((frame, idx) => (
-            <div key={`${idx}/${frame.refId}`}>
-              <h4>
-                {getFrameDisplayName(frame, idx)} ({frame.length})
-              </h4>
-              <table className="filter-table">
-                <thead>
-                  <tr>
-                    <td>Field</td>
-                    <td>Type</td>
-                    <td>Last</td>
-                  </tr>
-                </thead>
-                <tbody>
-                  {frame.fields.map((field, idx) => {
-                    const v = reducer.reduce!(field, false, false)[reducer.id];
-                    return (
-                      <tr key={`${idx}/${field.name}`}>
-                        <td>{getFieldDisplayName(field, frame, data.series)}</td>
-                        <td>{field.type}</td>
-                        <td>{`${v}`}</td>
-                      </tr>
-                    );
-                  })}
-                </tbody>
-              </table>
-            </div>
-          ))}
-      </div>
-    );
+    return <RenderInfoViewer {...this.props} />;
   }
 }

public/app/plugins/panel/debug/EventBusLogger.tsx

@@ -0,0 +1,75 @@
+import React, { PureComponent } from 'react';
+import { CustomScrollbar } from '@grafana/ui';
+import {
+  BusEvent,
+  CircularVector,
+  DataHoverPayload,
+  DataHoverEvent,
+  DataHoverClearEvent,
+  DataSelectEvent,
+  EventBus,
+  BusEventHandler,
+} from '@grafana/data';
+import { PartialObserver, Unsubscribable } from 'rxjs';
+
+interface Props {
+  eventBus: EventBus;
+}
+
+interface State {
+  isError?: boolean;
+  counter: number;
+}
+
+interface BusEventEx {
+  key: number;
+  type: string;
+  payload: DataHoverPayload;
+}
+let counter = 100;
+
+export class EventBusLoggerPanel extends PureComponent<Props, State> {
+  history = new CircularVector<BusEventEx>({ capacity: 40, append: 'head' });
+  subs: Unsubscribable[] = [];
+
+  constructor(props: Props) {
+    super(props);
+
+    this.state = { counter };
+
+    this.subs.push(props.eventBus.subscribe(DataHoverEvent, this.hoverHandler));
+    props.eventBus.getStream(DataHoverClearEvent).subscribe(this.eventObserver);
+    props.eventBus.getStream(DataSelectEvent).subscribe(this.eventObserver);
+  }
+
+  componentWillUnmount() {
+    for (const sub of this.subs) {
+      sub.unsubscribe();
+    }
+  }
+
+  hoverHandler: BusEventHandler<DataHoverEvent> = (event: DataHoverEvent) => {
+    this.history.add({
+      key: counter++,
+      type: event.type,
+      payload: event.payload,
+    });
+    this.setState({ counter });
+  };
+
+  eventObserver: PartialObserver<BusEvent> = {
+    next: (v: BusEvent) => {},
+  };
+
+  render() {
+    return (
+      <CustomScrollbar autoHeightMin="100%" autoHeightMax="100%">
+        {this.history.map((v, idx) => (
+          <div key={v.key}>
+            {v.key} {v.type} / X:{JSON.stringify(v.payload.x)} / Y:{JSON.stringify(v.payload.y)}
+          </div>
+        ))}
+      </CustomScrollbar>
+    );
+  }
+}

public/app/plugins/panel/debug/RenderInfoViewer.tsx

@@ -0,0 +1,109 @@
+import React, { Component } from 'react';
+import {
+  compareArrayValues,
+  compareDataFrameStructures,
+  fieldReducers,
+  getFieldDisplayName,
+  getFrameDisplayName,
+  PanelProps,
+  ReducerID,
+} from '@grafana/data';
+
+import { DebugPanelOptions, UpdateCounters, UpdateConfig } from './types';
+import { IconButton } from '@grafana/ui';
+
+type Props = PanelProps<DebugPanelOptions>;
+
+export class RenderInfoViewer extends Component<Props> {
+  // Intentionally not state to avoid overhead -- yes, things will be 1 tick behind
+  lastRender = Date.now();
+  counters: UpdateCounters = {
+    render: 0,
+    dataChanged: 0,
+    schemaChanged: 0,
+  };
+
+  shouldComponentUpdate(prevProps: Props) {
+    const { data, options } = this.props;
+
+    if (prevProps.data !== data) {
+      this.counters.dataChanged++;
+
+      if (options.counters?.schemaChanged) {
+        const oldSeries = prevProps.data?.series;
+        const series = data.series;
+        if (series && oldSeries) {
+          const sameStructure = compareArrayValues(series, oldSeries, compareDataFrameStructures);
+          if (!sameStructure) {
+            this.counters.schemaChanged++;
+          }
+        }
+      }
+    }
+    return true; // always render?
+  }
+
+  resetCounters = () => {
+    this.counters = {
+      render: 0,
+      dataChanged: 0,
+      schemaChanged: 0,
+    };
+    this.forceUpdate();
+  };
+
+  render() {
+    const { data, options } = this.props;
+    const showCounters = options.counters ?? ({} as UpdateConfig);
+    this.counters.render++;
+    const now = Date.now();
+    const elapsed = now - this.lastRender;
+    this.lastRender = now;
+
+    const reducer = fieldReducers.get(ReducerID.lastNotNull);
+
+    return (
+      <div>
+        <div>
+          <IconButton name="step-backward" title="reset counters" onClick={this.resetCounters} />
+          <span>
+            {showCounters.render && <span>Render: {this.counters.render}&nbsp;</span>}
+            {showCounters.dataChanged && <span>Data: {this.counters.dataChanged}&nbsp;</span>}
+            {showCounters.schemaChanged && <span>Schema: {this.counters.schemaChanged}&nbsp;</span>}
+            <span>TIME: {elapsed}ms</span>
+          </span>
+        </div>
+
+        {data.series &&
+          data.series.map((frame, idx) => (
+            <div key={`${idx}/${frame.refId}`}>
+              <h4>
+                {getFrameDisplayName(frame, idx)} ({frame.length})
+              </h4>
+              <table className="filter-table">
+                <thead>
+                  <tr>
+                    <td>Field</td>
+                    <td>Type</td>
+                    <td>Last</td>
+                  </tr>
+                </thead>
+                <tbody>
+                  {frame.fields.map((field, idx) => {
+                    const v = reducer.reduce!(field, false, false)[reducer.id];
+                    return (
+                      <tr key={`${idx}/${field.name}`}>
+                        <td>{getFieldDisplayName(field, frame, data.series)}</td>
+                        <td>{field.type}</td>
+                        <td>{`${v}`}</td>
+                      </tr>
+                    );
+                  })}
+                </tbody>
+              </table>
+            </div>
+          ))}
+      </div>
+    );
+  }
+}

public/app/plugins/panel/debug/module.tsx

@@ -1,22 +1,36 @@
 import { PanelPlugin } from '@grafana/data';
 import { DebugPanel } from './DebugPanel';
-import { DebugPanelOptions } from './types';
+import { DebugMode, DebugPanelOptions } from './types';
 
 export const plugin = new PanelPlugin<DebugPanelOptions>(DebugPanel).useFieldConfig().setPanelOptions((builder) => {
   builder
+    .addRadio({
+      path: 'mode',
+      name: 'Mode',
+      defaultValue: DebugMode.Render,
+      settings: {
+        options: [
+          { label: 'Render', value: DebugMode.Render },
+          { label: 'Events', value: DebugMode.Events },
+        ],
+      },
+    })
     .addBooleanSwitch({
       path: 'counters.render',
       name: 'Render Count',
       defaultValue: true,
+      showIf: ({ mode }) => mode === DebugMode.Render,
     })
     .addBooleanSwitch({
       path: 'counters.dataChanged',
       name: 'Data Changed Count',
       defaultValue: true,
+      showIf: ({ mode }) => mode === DebugMode.Render,
     })
     .addBooleanSwitch({
       path: 'counters.schemaChanged',
       name: 'Schema Changed Count',
       defaultValue: true,
+      showIf: ({ mode }) => mode === DebugMode.Render,
     });
 });

public/app/plugins/panel/debug/types.ts

@@ -8,6 +8,12 @@ export type UpdateCounters = {
   schemaChanged: number;
 };
 
+export enum DebugMode {
+  Render = 'render',
+  Events = 'events',
+}
+
 export interface DebugPanelOptions {
+  mode: DebugMode;
   counters?: UpdateConfig;
 }