refactor: reduce service switcher tearing

We render the location bar and notification banners separately for each
service and keep track of the BrowserView size separately for each
service to reduce the tearing that appears when people switch services.
The tearing cannot be eliminated completely, because it comes from the
separation between the main and renderer processes. But we can at least
try and reduce the IPC round-tripping and layout calculations required
to accurately position the services.

This approach has an overhead compared to the single
BrowserViewPlaceholder approach, because the renderer process has to
layout the location bar and notification for all services, not only the
selected one. The number of IPC messages during windows resize is also
increased. To compensate, we increase the throttle interval for resize
IPC messages and let electron itself resize the BrowserView between IPC
updates. (We must still keep pumping IPC messages during window resize,
because, e.g., changes in notification banner size due to re-layouting
will still affect the required BrowserView size).

If further reduction of IPC traffic is needed, we could implement
batching for resize IPC messages and more intelligent throttling via a
token bucker mechanism.

Signed-off-by: Kristóf Marussy <kristof@marussy.com>

14 files changed, 152 insertions, 102 deletions

diff --git a/packages/renderer/src/components/App.tsx b/packages/renderer/src/components/App.tsx
index d381abf..2f728e7 100644
--- a/packages/renderer/src/components/App.tsx
+++ b/packages/renderer/src/components/App.tsx
@@ -23,12 +23,8 @@ import { observer } from 'mobx-react-lite';
 import React, { useCallback, useEffect } from 'react';
 import { useTranslation } from 'react-i18next';
 
-import BrowserViewPlaceholder from './BrowserViewPlaceholder';
+import ServicePanel from './ServicePanel';
 import { useStore } from './StoreProvider';
-import InsecureConnectionBanner from './banner/InsecureConnectionBanner';
-import NewWindowBanner from './banner/NewWindowBanner';
-import ErrorPage from './errorPage/ErrorPage';
-import LocationBar from './locationBar/LocationBar';
 import Sidebar from './sidebar/Sidebar';
 
 function App({ devMode }: { devMode: boolean }): JSX.Element {
@@ -37,6 +33,7 @@ function App({ devMode }: { devMode: boolean }): JSX.Element {
   });
   const {
     settings: { selectedService },
+    shared: { services },
   } = useStore();
   const {
     settings: { name: serviceName },
@@ -95,20 +92,13 @@ function App({ devMode }: { devMode: boolean }): JSX.Element {
       <Box
         sx={{
           flex: 1,
-          display: 'flex',
-          overflow: 'hidden',
-          flexDirection: 'column',
-          alignItems: 'stretch',
           height: '100%',
-          zIndex: 100,
+          position: 'relative',
         }}
       >
-        <LocationBar />
-        <InsecureConnectionBanner service={selectedService} />
-        <NewWindowBanner service={selectedService} />
-        <BrowserViewPlaceholder>
-          <ErrorPage service={selectedService} />
-        </BrowserViewPlaceholder>
+        {services.map((service) => (
+          <ServicePanel key={service.id} service={service} />
+        ))}
       </Box>
     </Box>
   );
diff --git a/packages/renderer/src/components/BrowserViewPlaceholder.tsx b/packages/renderer/src/components/BrowserViewPlaceholder.tsx
index 9bd1176..2bfc9b0 100644
--- a/packages/renderer/src/components/BrowserViewPlaceholder.tsx
+++ b/packages/renderer/src/components/BrowserViewPlaceholder.tsx
@@ -22,29 +22,29 @@ import Box from '@mui/material/Box';
 import throttle from 'lodash-es/throttle';
 import React, { ReactNode, useCallback, useRef } from 'react';
 
-import { useStore } from './StoreProvider';
+import Service from '../stores/Service';
 
 function BrowserViewPlaceholder({
+  service,
   children,
 }: {
+  service: Service;
   children?: ReactNode;
 }): JSX.Element {
-  const store = useStore();
-
   // eslint-disable-next-line react-hooks/exhaustive-deps -- react-hooks doesn't support `throttle`.
   const onResize = useCallback(
     throttle(([entry]: ResizeObserverEntry[]) => {
       if (entry) {
         const { x, y, width, height } = entry.target.getBoundingClientRect();
-        store.setBrowserViewBounds({
+        service.setBrowserViewBounds({
           x: Math.round(x),
           y: Math.round(y),
           width: Math.round(width),
           height: Math.round(height),
         });
       }
-    }, 40),
-    [store],
+    }, 100),
+    [service],
   );
 
   const resizeObserverRef = useRef<ResizeObserver | undefined>();
@@ -61,7 +61,7 @@ function BrowserViewPlaceholder({
       resizeObserverRef.current = new ResizeObserver(onResize);
       resizeObserverRef.current.observe(element);
     },
-    [onResize, resizeObserverRef],
+    [onResize],
   );
 
   return (
diff --git a/packages/renderer/src/components/ServicePanel.tsx b/packages/renderer/src/components/ServicePanel.tsx
new file mode 100644
index 0000000..de58d24
--- /dev/null
+++ b/packages/renderer/src/components/ServicePanel.tsx
@@ -0,0 +1,76 @@
+/*
+ * Copyright (C)  2021-2022 Kristóf Marussy <kristof@marussy.com>
+ *
+ * This file is part of Sophie.
+ *
+ * Sophie is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import Box from '@mui/material/Box';
+import { observer } from 'mobx-react-lite';
+import React from 'react';
+
+import Service from '../stores/Service';
+
+import BrowserViewPlaceholder from './BrowserViewPlaceholder';
+import { useStore } from './StoreProvider';
+import InsecureConnectionBanner from './banner/InsecureConnectionBanner';
+import NewWindowBanner from './banner/NewWindowBanner';
+import ErrorPage from './errorPage/ErrorPage';
+import LocationBar from './locationBar/LocationBar';
+
+export function getServicePanelID(service: Service): string {
+  return `Sophie-${service.id}-ServicePanel`;
+}
+
+function ServicePanel({ service }: { service: Service }): JSX.Element {
+  const {
+    settings: { selectedService },
+  } = useStore();
+
+  const {
+    settings: { name },
+  } = service;
+  const visible = service === selectedService;
+
+  return (
+    <Box
+      id={getServicePanelID(service)}
+      role="tabpanel"
+      aria-label={name}
+      sx={{
+        position: 'absolute',
+        top: 0,
+        left: 0,
+        bottom: 0,
+        right: 0,
+        display: 'flex',
+        overflow: 'hidden',
+        visibility: visible ? 'visible' : 'hidden',
+        flexDirection: 'column',
+        alignItems: 'stretch',
+      }}
+    >
+      <LocationBar service={service} />
+      <InsecureConnectionBanner service={service} />
+      <NewWindowBanner service={service} />
+      <BrowserViewPlaceholder service={service}>
+        <ErrorPage service={service} />
+      </BrowserViewPlaceholder>
+    </Box>
+  );
+}
+
+export default observer(ServicePanel);
diff --git a/packages/renderer/src/components/banner/InsecureConnectionBanner.tsx b/packages/renderer/src/components/banner/InsecureConnectionBanner.tsx
index 7a03fce..0b70db6 100644
--- a/packages/renderer/src/components/banner/InsecureConnectionBanner.tsx
+++ b/packages/renderer/src/components/banner/InsecureConnectionBanner.tsx
@@ -34,17 +34,12 @@ import NotificationBanner from './NotificationBanner';
 function InsecureConnectionBanner({
   service,
 }: {
-  service: Service | undefined;
+  service: Service;
 }): JSX.Element | null {
   const { t } = useTranslation(undefined, {
     keyPrefix: 'banner.insecureConnection',
   });
 
-  if (service === undefined) {
-    // eslint-disable-next-line unicorn/no-null -- React requires `null` to skip rendering.
-    return null;
-  }
-
   const {
     canReconnectSecurely,
     hasError,
diff --git a/packages/renderer/src/components/banner/NewWindowBanner.tsx b/packages/renderer/src/components/banner/NewWindowBanner.tsx
index 478de8e..07fafda 100644
--- a/packages/renderer/src/components/banner/NewWindowBanner.tsx
+++ b/packages/renderer/src/components/banner/NewWindowBanner.tsx
@@ -32,17 +32,12 @@ import NotificationBanner from './NotificationBanner';
 function NewWindowBanner({
   service,
 }: {
-  service: Service | undefined;
+  service: Service;
 }): JSX.Element | null {
   const { t } = useTranslation(undefined, {
     keyPrefix: 'banner.newWindow',
   });
 
-  if (service === undefined) {
-    // eslint-disable-next-line unicorn/no-null -- React requires `null` to skip rendering.
-    return null;
-  }
-
   const {
     popups,
     settings: { name },
diff --git a/packages/renderer/src/components/errorPage/ErrorPage.tsx b/packages/renderer/src/components/errorPage/ErrorPage.tsx
index 99ca020..10f54cd 100644
--- a/packages/renderer/src/components/errorPage/ErrorPage.tsx
+++ b/packages/renderer/src/components/errorPage/ErrorPage.tsx
@@ -123,14 +123,10 @@ function formatError(service: Service, t: TFunction): ErrorDetails {
   }
 }
 
-function ErrorPage({
-  service,
-}: {
-  service: Service | undefined;
-}): JSX.Element | null {
+function ErrorPage({ service }: { service: Service }): JSX.Element | null {
   const { t } = useTranslation(undefined);
 
-  if (service === undefined || !service.hasError) {
+  if (!service.hasError) {
     // eslint-disable-next-line unicorn/no-null -- React requires `null` to skip rendering.
     return null;
   }
diff --git a/packages/renderer/src/components/locationBar/ExtraButtons.tsx b/packages/renderer/src/components/locationBar/ExtraButtons.tsx
index ef90199..4d4c3c4 100644
--- a/packages/renderer/src/components/locationBar/ExtraButtons.tsx
+++ b/packages/renderer/src/components/locationBar/ExtraButtons.tsx
@@ -27,11 +27,7 @@ import { useTranslation } from 'react-i18next';
 
 import type Service from '../../stores/Service';
 
-function ExtraButtons({
-  service,
-}: {
-  service: Service | undefined;
-}): JSX.Element {
+function ExtraButtons({ service }: { service: Service }): JSX.Element {
   const { t } = useTranslation(undefined, {
     keyPrefix: 'toolbar',
   });
@@ -40,8 +36,8 @@ function ExtraButtons({
     <Box display="flex">
       <IconButton
         aria-label={t('openInBrowser')}
-        disabled={service?.currentUrl === undefined}
-        onClick={() => service?.openCurrentURLInExternalBrowser()}
+        disabled={service.currentUrl === undefined}
+        onClick={() => service.openCurrentURLInExternalBrowser()}
       >
         <IconOpenInBrowser />
       </IconButton>
diff --git a/packages/renderer/src/components/locationBar/LocationBar.tsx b/packages/renderer/src/components/locationBar/LocationBar.tsx
index 54ead8e..c290722 100644
--- a/packages/renderer/src/components/locationBar/LocationBar.tsx
+++ b/packages/renderer/src/components/locationBar/LocationBar.tsx
@@ -22,13 +22,16 @@ import { styled } from '@mui/material/styles';
 import { observer } from 'mobx-react-lite';
 import React from 'react';
 
+import type Service from '../../stores/Service';
 import { useStore } from '../StoreProvider';
 
 import ExtraButtons from './ExtraButtons';
 import LocationTextField from './LocationTextField';
 import NavigationButtons from './NavigationButtons';
 
-export const LOCATION_BAR_ID = 'Sophie-LocationBar';
+export function getLocaltionBarID(service: Service): string {
+  return `Sophie-${service.id}-LocationBar`;
+}
 
 const LocationBarRoot = styled('header', {
   name: 'LocationBar',
@@ -41,17 +44,22 @@ const LocationBarRoot = styled('header', {
   borderBottom: `1px solid ${theme.palette.divider}`,
 }));
 
-function LocationBar(): JSX.Element {
+function LocationBar({ service }: { service: Service }): JSX.Element {
   const {
-    shared: { locationBarVisible },
-    settings: { selectedService },
+    settings: { showLocationBar },
   } = useStore();
 
+  const { alwaysShowLocationBar } = service;
+  const locationBarVisible = showLocationBar || alwaysShowLocationBar;
+
   return (
-    <LocationBarRoot id={LOCATION_BAR_ID} hidden={!locationBarVisible}>
-      <NavigationButtons service={selectedService} />
-      <LocationTextField service={selectedService} />
-      <ExtraButtons service={selectedService} />
+    <LocationBarRoot
+      id={getLocaltionBarID(service)}
+      hidden={!locationBarVisible}
+    >
+      <NavigationButtons service={service} />
+      <LocationTextField service={service} />
+      <ExtraButtons service={service} />
     </LocationBarRoot>
   );
 }
diff --git a/packages/renderer/src/components/locationBar/LocationTextField.tsx b/packages/renderer/src/components/locationBar/LocationTextField.tsx
index 85cf794..1d6b561 100644
--- a/packages/renderer/src/components/locationBar/LocationTextField.tsx
+++ b/packages/renderer/src/components/locationBar/LocationTextField.tsx
@@ -20,7 +20,6 @@
 
 import FilledInput from '@mui/material/FilledInput';
 import { styled } from '@mui/material/styles';
-import { SecurityLabelKind } from '@sophie/shared';
 import { autorun } from 'mobx';
 import { observer } from 'mobx-react-lite';
 import React, { useCallback, useEffect, useState } from 'react';
@@ -44,19 +43,15 @@ const LocationTextFieldRoot = styled(FilledInput, {
   },
 }));
 
-function LocationTextField({
-  service,
-}: {
-  service: Service | undefined;
-}): JSX.Element {
+function LocationTextField({ service }: { service: Service }): JSX.Element {
   const [inputFocused, setInputFocused] = useState(false);
   const [changed, setChanged] = useState(false);
   const [value, setValue] = useState('');
 
   const resetValue = useCallback(() => {
-    setValue(service?.currentUrl ?? '');
+    setValue(service.currentUrl ?? '');
     setChanged(false);
-  }, [service, setChanged, setValue]);
+  }, [service]);
 
   useEffect(
     () =>
@@ -84,8 +79,8 @@ function LocationTextField({
         overlayVisible: !inputFocused && !changed,
         overlay: (
           <UrlOverlay
-            url={service?.currentUrl ?? ''}
-            alert={service?.hasSecurityLabelWarning ?? false}
+            url={service.currentUrl ?? ''}
+            alert={service.hasSecurityLabelWarning ?? false}
           />
         ),
       }}
@@ -102,7 +97,7 @@ function LocationTextField({
             resetValue();
             break;
           case 'Enter':
-            service?.go(value);
+            service.go(value);
             break;
           default:
             // Nothing to do, let the key event through.
@@ -117,14 +112,14 @@ function LocationTextField({
       disableUnderline
       startAdornment={
         <SecurityLabel
-          kind={service?.securityLabel ?? SecurityLabelKind.Empty}
+          kind={service.securityLabel}
           changed={changed}
           position="start"
         />
       }
       endAdornment={
         changed ? (
-          <GoButton onClick={() => service?.go(value)} position="end" />
+          <GoButton onClick={() => service.go(value)} position="end" />
         ) : undefined
       }
       value={value}
diff --git a/packages/renderer/src/components/locationBar/NavigationButtons.tsx b/packages/renderer/src/components/locationBar/NavigationButtons.tsx
index 9c4ebdb..96e40e7 100644
--- a/packages/renderer/src/components/locationBar/NavigationButtons.tsx
+++ b/packages/renderer/src/components/locationBar/NavigationButtons.tsx
@@ -32,11 +32,7 @@ import { useTranslation } from 'react-i18next';
 
 import type Service from '../../stores/Service';
 
-function NavigationButtons({
-  service,
-}: {
-  service: Service | undefined;
-}): JSX.Element {
+function NavigationButtons({ service }: { service: Service }): JSX.Element {
   const { t } = useTranslation(undefined, {
     keyPrefix: 'toolbar',
   });
@@ -46,36 +42,31 @@ function NavigationButtons({
     <Box display="flex">
       <IconButton
         aria-label={t('back')}
-        disabled={service === undefined || !service.canGoBack}
-        onClick={() => service?.goBack()}
+        disabled={!service.canGoBack}
+        onClick={() => service.goBack()}
       >
         {direction === 'ltr' ? <IconArrowBack /> : <IconArrowForward />}
       </IconButton>
       <IconButton
         aria-label={t('forward')}
-        disabled={service === undefined || !service.canGoForward}
-        onClick={() => service?.goForward()}
+        disabled={!service.canGoForward}
+        onClick={() => service.goForward()}
       >
         {direction === 'ltr' ? <IconArrowForward /> : <IconArrowBack />}
       </IconButton>
-      {service?.loading ?? false ? (
-        <IconButton aria-label={t('stop')} onClick={() => service?.stop()}>
+      {service.loading ? (
+        <IconButton aria-label={t('stop')} onClick={() => service.stop()}>
           <IconStop />
         </IconButton>
       ) : (
         <IconButton
           aria-label={t('reload')}
-          disabled={service === undefined}
-          onClick={(event) => service?.reload(event.shiftKey)}
+          onClick={(event) => service.reload(event.shiftKey)}
         >
           <IconRefresh />
         </IconButton>
       )}
-      <IconButton
-        aria-label={t('home')}
-        disabled={service === undefined}
-        onClick={() => service?.goHome()}
-      >
+      <IconButton aria-label={t('home')} onClick={() => service.goHome()}>
         <IconHome />
       </IconButton>
     </Box>
diff --git a/packages/renderer/src/components/sidebar/ServiceSwitcher.tsx b/packages/renderer/src/components/sidebar/ServiceSwitcher.tsx
index 0ebd359..24cfd0c 100644
--- a/packages/renderer/src/components/sidebar/ServiceSwitcher.tsx
+++ b/packages/renderer/src/components/sidebar/ServiceSwitcher.tsx
@@ -27,6 +27,7 @@ import React from 'react';
 import { useTranslation } from 'react-i18next';
 
 import type Service from '../../stores/Service';
+import { getServicePanelID } from '../ServicePanel';
 import { useStore } from '../StoreProvider';
 
 import ServiceIcon from './ServiceIcon';
@@ -112,6 +113,7 @@ function ServiceSwitcher(): JSX.Element {
           value={service.id}
           icon={<ServiceIcon service={service} />}
           aria-label={getServiceTitle(service, t)}
+          aria-controls={getServicePanelID(service)}
         />
       ))}
     </ServiceSwitcherRoot>
diff --git a/packages/renderer/src/components/sidebar/ToggleLocationBarButton.tsx b/packages/renderer/src/components/sidebar/ToggleLocationBarButton.tsx
index 7fc559d..c697170 100644
--- a/packages/renderer/src/components/sidebar/ToggleLocationBarButton.tsx
+++ b/packages/renderer/src/components/sidebar/ToggleLocationBarButton.tsx
@@ -28,7 +28,7 @@ import React from 'react';
 import { useTranslation } from 'react-i18next';
 
 import { useStore } from '../StoreProvider';
-import { LOCATION_BAR_ID } from '../locationBar/LocationBar';
+import { getLocaltionBarID } from '../locationBar/LocationBar';
 
 function ToggleLocationBarIcon({
   loading,
@@ -54,13 +54,17 @@ function ToggleLocationBarButton(): JSX.Element {
   const { selectedService } = settings;
 
   return (
+    /* eslint-disable react/jsx-props-no-spreading -- Conditionally set the aria-controls prop. */
     <IconButton
       disabled={!canToggleLocationBar}
       aria-pressed={locationBarVisible}
-      aria-controls={LOCATION_BAR_ID}
+      {...(selectedService === undefined
+        ? {}
+        : { 'aria-controls': getLocaltionBarID(selectedService) })}
       aria-label={t('toolbar.toggleLocationBar')}
       onClick={() => settings.toggleLocationBar()}
     >
+      {/* eslint-enable react/jsx-props-no-spreading */}
       <ToggleLocationBarIcon
         loading={selectedService?.loading ?? false}
         show={locationBarVisible}
diff --git a/packages/renderer/src/stores/RendererStore.ts b/packages/renderer/src/stores/RendererStore.ts
index 7052162..a3983ca 100644
--- a/packages/renderer/src/stores/RendererStore.ts
+++ b/packages/renderer/src/stores/RendererStore.ts
@@ -18,14 +18,14 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
-import { BrowserViewBounds, SophieRenderer } from '@sophie/shared';
+import type { SophieRenderer } from '@sophie/shared';
 import { applySnapshot, applyPatch, Instance, types } from 'mobx-state-tree';
 
 import { getLogger } from '../utils/log';
 
-import GlobalSettings from './GlobalSettings';
-import RendererEnv, { getEnv } from './RendererEnv';
-import Service from './Service';
+import type GlobalSettings from './GlobalSettings';
+import type RendererEnv from './RendererEnv';
+import type Service from './Service';
 import SharedStore from './SharedStore';
 
 const log = getLogger('RendererStore');
@@ -41,14 +41,6 @@ const RendererStore = types
     get services(): Service[] {
       return self.shared.services;
     },
-  }))
-  .actions((self) => ({
-    setBrowserViewBounds(browserViewBounds: BrowserViewBounds): void {
-      getEnv(self).dispatchMainAction({
-        action: 'set-browser-view-bounds',
-        browserViewBounds,
-      });
-    },
   }));
 
 /*
diff --git a/packages/renderer/src/stores/Service.ts b/packages/renderer/src/stores/Service.ts
index dcaf96e..c8d513f 100644
--- a/packages/renderer/src/stores/Service.ts
+++ b/packages/renderer/src/stores/Service.ts
@@ -18,7 +18,11 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
-import { defineServiceModel, ServiceAction } from '@sophie/shared';
+import {
+  BrowserViewBounds,
+  defineServiceModel,
+  ServiceAction,
+} from '@sophie/shared';
 import { Instance } from 'mobx-state-tree';
 
 import { getEnv } from './RendererEnv';
@@ -49,6 +53,12 @@ const Service = defineServiceModel(ServiceSettings)
     }
 
     return {
+      setBrowserViewBounds(browserViewBounds: BrowserViewBounds): void {
+        dispatch({
+          action: 'set-browser-view-bounds',
+          browserViewBounds,
+        });
+      },
       goBack(): void {
         dispatch({
           action: 'back',