Dashboards: Use IntersectionObserver to manage lazy loading of panels (#42834)

public/app/features/dashboard/components/PanelEditor/PanelEditor.tsx

@@ -253,7 +253,7 @@ export class PanelEditorUnconnected extends PureComponent<Props> {
                       panel={panel}
                       isEditing={true}
                       isViewing={false}
-                      isInView={true}
+                      lazy={false}
                       width={panelSize.width}
                       height={panelSize.height}
                       skipStateCleanUp={true}

public/app/features/dashboard/containers/DashboardPage.test.tsx

@@ -2,6 +2,7 @@ import React from 'react';
 import { Provider } from 'react-redux';
 import { render, screen } from '@testing-library/react';
 import { Props, UnthemedDashboardPage } from './DashboardPage';
+import { Props as LazyLoaderProps } from '../dashgrid/LazyLoader';
 import { Router } from 'react-router-dom';
 import { locationService, setDataSourceSrv } from '@grafana/runtime';
 import { DashboardModel } from '../state';
@@ -14,6 +15,13 @@ import { getRouteComponentProps } from 'app/core/navigation/__mocks__/routeProps
 import { createTheme } from '@grafana/data';
 import { AutoSizerProps } from 'react-virtualized-auto-sizer';
 
+jest.mock('app/features/dashboard/dashgrid/LazyLoader', () => {
+  const LazyLoader = ({ children }: Pick<LazyLoaderProps, 'children'>) => {
+    return <>{typeof children === 'function' ? children({ isInView: true }) : children}</>;
+  };
+  return { LazyLoader };
+});
+
 jest.mock('app/features/dashboard/components/DashboardSettings/GeneralSettings', () => {
   class GeneralSettings extends React.Component<{}, {}> {
     render() {

public/app/features/dashboard/containers/DashboardPage.tsx

@@ -3,7 +3,7 @@ import { css } from '@emotion/css';
 import { connect, ConnectedProps } from 'react-redux';
 import { locationService } from '@grafana/runtime';
 import { selectors } from '@grafana/e2e-selectors';
-import { CustomScrollbar, ScrollbarPosition, stylesFactory, Themeable2, withTheme2 } from '@grafana/ui';
+import { CustomScrollbar, stylesFactory, Themeable2, withTheme2 } from '@grafana/ui';
 
 import { createErrorNotification } from 'app/core/copy/appNotification';
 import { Branding } from 'app/core/components/Branding/Branding';
@@ -75,7 +75,6 @@ export type Props = Themeable2 &
 export interface State {
   editPanel: PanelModel | null;
   viewPanel: PanelModel | null;
-  scrollTop: number;
   updateScrollTop?: number;
   rememberScrollTop: number;
   showLoadingState: boolean;
@@ -92,7 +91,6 @@ export class UnthemedDashboardPage extends PureComponent<Props, State> {
       editPanel: null,
       viewPanel: null,
       showLoadingState: false,
-      scrollTop: 0,
       rememberScrollTop: 0,
       panelNotFound: false,
       editPanelAccessDenied: false,
@@ -252,7 +250,6 @@ export class UnthemedDashboardPage extends PureComponent<Props, State> {
       return {
         ...state,
         viewPanel: panel,
-        rememberScrollTop: state.scrollTop,
         updateScrollTop: 0,
       };
     }
@@ -273,10 +270,6 @@ export class UnthemedDashboardPage extends PureComponent<Props, State> {
     return state;
   }
 
-  setScrollTop = ({ scrollTop }: ScrollbarPosition): void => {
-    this.setState({ scrollTop, updateScrollTop: undefined });
-  };
-
   onAddPanel = () => {
     const { dashboard } = this.props;
 
@@ -320,7 +313,7 @@ export class UnthemedDashboardPage extends PureComponent<Props, State> {
 
   render() {
     const { dashboard, isInitSlow, initError, queryParams, theme } = this.props;
-    const { editPanel, viewPanel, scrollTop, updateScrollTop } = this.state;
+    const { editPanel, viewPanel, updateScrollTop } = this.state;
     const kioskMode = getKioskMode(queryParams.kiosk);
     const styles = getStyles(theme, kioskMode);
 
@@ -332,8 +325,6 @@ export class UnthemedDashboardPage extends PureComponent<Props, State> {
       return null;
     }
 
-    // Only trigger render when the scroll has moved by 25
-    const approximateScrollTop = Math.round(scrollTop / 25) * 25;
     const inspectPanel = this.getInspectPanel();
     const containerClassNames = classnames(styles.dashboardContainer, {
       'panel-in-fullscreen': viewPanel,
@@ -361,7 +352,6 @@ export class UnthemedDashboardPage extends PureComponent<Props, State> {
         <div className={styles.dashboardScroll}>
           <CustomScrollbar
             autoHeightMin="100%"
-            setScrollTop={this.setScrollTop}
             scrollTop={updateScrollTop}
             hideHorizontalTrack={true}
             updateAfterMountMs={500}
@@ -374,12 +364,7 @@ export class UnthemedDashboardPage extends PureComponent<Props, State> {
                 </section>
               )}
 
-              <DashboardGrid
-                dashboard={dashboard}
-                viewPanel={viewPanel}
-                editPanel={editPanel}
-                scrollTop={approximateScrollTop}
-              />
+              <DashboardGrid dashboard={dashboard} viewPanel={viewPanel} editPanel={editPanel} />
             </div>
           </CustomScrollbar>
         </div>

public/app/features/dashboard/containers/SoloPanelPage.tsx

@@ -115,7 +115,7 @@ export const SoloPanel = ({ dashboard, notFound, panel, panelId }: SoloPanelProp
               panel={panel}
               isEditing={false}
               isViewing={false}
-              isInView={true}
+              lazy={false}
             />
           );
         }}

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

@@ -3,6 +3,13 @@ import { shallow, ShallowWrapper } from 'enzyme';
 import { DashboardGrid, Props } from './DashboardGrid';
 import { DashboardModel } from '../state';
 
+jest.mock('app/features/dashboard/dashgrid/LazyLoader', () => {
+  const LazyLoader: React.FC = ({ children }) => {
+    return <>{children}</>;
+  };
+  return { LazyLoader };
+});
+
 interface ScenarioContext {
   props: Props;
   wrapper?: ShallowWrapper<Props, any, DashboardGrid>;
@@ -59,7 +66,6 @@ function dashboardGridScenario(description: string, scenarioFn: (ctx: ScenarioCo
       props: {
         editPanel: null,
         viewPanel: null,
-        scrollTop: 0,
         dashboard: getTestDashboard(),
       },
       setProps: (props: Partial<Props>) => {

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

@@ -21,7 +21,6 @@ export interface Props {
   dashboard: DashboardModel;
   editPanel: PanelModel | null;
   viewPanel: PanelModel | null;
-  scrollTop: number;
 }
 
 export interface State {
@@ -125,32 +124,6 @@ export class DashboardGrid extends PureComponent<Props, State> {
     this.updateGridPos(newItem, layout);
   };
 
-  isInView(panel: PanelModel, gridWidth: number) {
-    if (panel.isViewing || panel.isEditing) {
-      return true;
-    }
-
-    const scrollTop = this.props.scrollTop;
-    const screenPos = this.getPanelScreenPos(panel, gridWidth);
-
-    // Show things that are almost in the view
-    const buffer = 100;
-
-    // The panel is above the viewport
-    if (scrollTop > screenPos.bottom + buffer) {
-      return false;
-    }
-
-    const scrollViewBottom = scrollTop + this.windowHeight;
-
-    // Panel is below view
-    if (screenPos.top > scrollViewBottom + buffer) {
-      return false;
-    }
-
-    return !this.props.dashboard.otherPanelInFullscreen(panel);
-  }
-
   getPanelScreenPos(panel: PanelModel, gridWidth: number): { top: number; bottom: number } {
     let top = 0;
 
@@ -185,9 +158,6 @@ export class DashboardGrid extends PureComponent<Props, State> {
     for (const panel of this.props.dashboard.panels) {
       const panelClasses = classNames({ 'react-grid-item--fullscreen': panel.isViewing });
 
-      // Update is in view state
-      panel.isInView = this.isInView(panel, gridWidth);
-
       panelElements.push(
         <GrafanaGridItem
           key={panel.key}
@@ -226,7 +196,6 @@ export class DashboardGrid extends PureComponent<Props, State> {
         dashboard={this.props.dashboard}
         isEditing={panel.isEditing}
         isViewing={panel.isViewing}
-        isInView={panel.isInView}
         width={width}
         height={height}
       />
@@ -235,13 +204,14 @@ export class DashboardGrid extends PureComponent<Props, State> {
 
   render() {
     const { dashboard } = this.props;
+
+    /**
+     * We have a parent with "flex: 1 1 0" we need to reset it to "flex: 1 1 auto" to have the AutoSizer
+     * properly working. For more information go here:
+     * https://github.com/bvaughn/react-virtualized/blob/master/docs/usingAutoSizer.md#can-i-use-autosizer-within-a-flex-container
+     */
     return (
-      /**
-       * We have a parent with "flex: 1 1 0" we need to reset it to "flex: 1 1 auto" to have the AutoSizer
-       * properly working. For more information go here:
-       * https://github.com/bvaughn/react-virtualized/blob/master/docs/usingAutoSizer.md#can-i-use-autosizer-within-a-flex-container
-       */
-      <div style={{ flex: '1 1 auto' }}>
+      <div style={{ flex: '1 1 auto', display: this.props.editPanel ? 'none' : undefined }}>
         <AutoSizer disableHeight>
           {({ width }) => {
             if (width === 0) {

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

@@ -7,6 +7,7 @@ import { StoreState } from 'app/types';
 import { PanelPlugin } from '@grafana/data';
 import { cleanUpPanelState, setPanelInstanceState } from '../../panel/state/reducers';
 import { initPanelState } from '../../panel/state/actions';
+import { LazyLoader } from './LazyLoader';
 
 export interface OwnProps {
   panel: PanelModel;
@@ -14,14 +15,10 @@ export interface OwnProps {
   dashboard: DashboardModel;
   isEditing: boolean;
   isViewing: boolean;
-  isInView: boolean;
   width: number;
   height: number;
   skipStateCleanUp?: boolean;
-}
-
-export interface State {
-  isLazy: boolean;
+  lazy?: boolean;
 }
 
 const mapStateToProps = (state: StoreState, props: OwnProps) => {
@@ -46,18 +43,15 @@ const connector = connect(mapStateToProps, mapDispatchToProps);
 
 export type Props = OwnProps & ConnectedProps<typeof connector>;
 
-export class DashboardPanelUnconnected extends PureComponent<Props, State> {
-  specialPanels: { [key: string]: Function } = {};
-
-  constructor(props: Props) {
-    super(props);
+export class DashboardPanelUnconnected extends PureComponent<Props> {
+  static defaultProps: Partial<Props> = {
+    lazy: true,
+  };
 
-    this.state = {
-      isLazy: !props.isInView,
-    };
-  }
+  specialPanels: { [key: string]: Function } = {};
 
   componentDidMount() {
+    this.props.panel.isInView = !this.props.lazy;
     if (!this.props.plugin) {
       this.props.initPanelState(this.props.panel);
     }
@@ -70,21 +64,19 @@ export class DashboardPanelUnconnected extends PureComponent<Props, State> {
     }
   }
 
-  componentDidUpdate() {
-    if (this.state.isLazy && this.props.isInView) {
-      this.setState({ isLazy: false });
-    }
-  }
-
   onInstanceStateChange = (value: any) => {
     this.props.setPanelInstanceState({ key: this.props.stateKey, value });
   };
 
+  onVisibilityChange = (v: boolean) => {
+    this.props.panel.isInView = v;
+  };
+
   renderPanel(plugin: PanelPlugin) {
-    const { dashboard, panel, isViewing, isInView, isEditing, width, height } = this.props;
+    const { dashboard, panel, isViewing, isEditing, width, height, lazy } = this.props;
 
-    if (plugin.angularPanelCtrl) {
-      return (
+    const renderPanelChrome = (isInView: boolean) =>
+      plugin.angularPanelCtrl ? (
         <PanelChromeAngular
           plugin={plugin}
           panel={panel}
@@ -95,38 +87,37 @@ export class DashboardPanelUnconnected extends PureComponent<Props, State> {
           width={width}
           height={height}
         />
+      ) : (
+        <PanelChrome
+          plugin={plugin}
+          panel={panel}
+          dashboard={dashboard}
+          isViewing={isViewing}
+          isEditing={isEditing}
+          isInView={isInView}
+          width={width}
+          height={height}
+          onInstanceStateChange={this.onInstanceStateChange}
+        />
       );
-    }
 
-    return (
-      <PanelChrome
-        plugin={plugin}
-        panel={panel}
-        dashboard={dashboard}
-        isViewing={isViewing}
-        isEditing={isEditing}
-        isInView={isInView}
-        width={width}
-        height={height}
-        onInstanceStateChange={this.onInstanceStateChange}
-      />
+    return lazy ? (
+      <LazyLoader width={width} height={height} onChange={this.onVisibilityChange}>
+        {({ isInView }) => renderPanelChrome(isInView)}
+      </LazyLoader>
+    ) : (
+      renderPanelChrome(true)
     );
   }
 
   render() {
     const { plugin } = this.props;
-    const { isLazy } = this.state;
 
     // If we have not loaded plugin exports yet, wait
     if (!plugin) {
       return null;
     }
 
-    // If we are lazy state don't render anything
-    if (isLazy) {
-      return null;
-    }
-
     return this.renderPanel(plugin);
   }
 }

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

@@ -0,0 +1,57 @@
+import React, { useRef, useState } from 'react';
+import { useUniqueId } from 'app/plugins/datasource/influxdb/components/useUniqueId';
+import { useEffectOnce } from 'react-use';
+
+export interface Props {
+  children: React.ReactNode | (({ isInView }: { isInView: boolean }) => React.ReactNode);
+  width?: number;
+  height?: number;
+  onLoad?: () => void;
+  onChange?: (isInView: boolean) => void;
+}
+
+export function LazyLoader({ children, width, height, onLoad, onChange }: Props) {
+  const id = useUniqueId();
+  const [loaded, setLoaded] = useState(false);
+  const [isInView, setIsInView] = useState(false);
+  const wrapperRef = useRef<HTMLDivElement>(null);
+  useEffectOnce(() => {
+    LazyLoader.addCallback(id, (entry) => {
+      if (!loaded && entry.isIntersecting) {
+        setLoaded(true);
+        onLoad?.();
+      }
+
+      setIsInView(entry.isIntersecting);
+      onChange?.(entry.isIntersecting);
+    });
+
+    if (wrapperRef.current) {
+      LazyLoader.observer.observe(wrapperRef.current);
+    }
+
+    return () => {
+      delete LazyLoader.callbacks[id];
+      if (Object.keys(LazyLoader.callbacks).length === 0) {
+        LazyLoader.observer.disconnect();
+      }
+    };
+  });
+
+  return (
+    <div id={id} ref={wrapperRef} style={{ width, height }}>
+      {loaded && (typeof children === 'function' ? children({ isInView }) : children)}
+    </div>
+  );
+}
+
+LazyLoader.callbacks = {} as Record<string, (e: IntersectionObserverEntry) => void>;
+LazyLoader.addCallback = (id: string, c: (e: IntersectionObserverEntry) => void) => (LazyLoader.callbacks[id] = c);
+LazyLoader.observer = new IntersectionObserver(
+  (entries) => {
+    for (const entry of entries) {
+      LazyLoader.callbacks[entry.target.id](entry);
+    }
+  },
+  { rootMargin: '100px' }
+);

public/app/features/dashboard/dashgrid/__snapshots__/DashboardGrid.test.tsx.snap

@@ -4,6 +4,7 @@ exports[`DashboardGrid Can render dashboard grid Should render 1`] = `
 <div
   style={
     Object {
+      "display": undefined,
       "flex": "1 1 auto",
     }
   }