Force canvas redraw when system theme changes

src/components/shared/chart/Canvas.tsx

@@ -375,6 +375,18 @@ export class ChartCanvas<Item> extends React.Component<
     }
   }
 
+  override componentDidMount() {
+    window.addEventListener('profiler-theme-change', this._onThemeChange);
+  }
+
+  override componentWillUnmount() {
+    window.removeEventListener('profiler-theme-change', this._onThemeChange);
+  }
+
+  _onThemeChange = () => {
+    this._scheduleDraw();
+  };
+
   override componentDidUpdate(prevProps: Props<Item>, prevState: State<Item>) {
     if (prevProps !== this.props) {
       if (

src/components/shared/thread/ActivityGraphCanvas.tsx

@@ -105,8 +105,20 @@ export class ActivityGraphCanvas extends React.PureComponent<CanvasProps> {
 
   override componentDidMount() {
     this._renderCanvas();
+    window.addEventListener('profiler-theme-change', this._onThemeChange);
   }
 
+  override componentWillUnmount() {
+    window.removeEventListener('profiler-theme-change', this._onThemeChange);
+  }
+
+  _onThemeChange = () => {
+    // Invalidate the cached category draw styles,
+    // so they are recreated with the new theme colors.
+    this._categoryDrawStyles = null;
+    this._renderCanvas();
+  };
+
   override componentDidUpdate() {
     this._renderCanvas();
   }

src/components/shared/thread/SampleGraph.tsx

@@ -119,8 +119,17 @@ class ThreadSampleGraphCanvas extends React.PureComponent<CanvasProps> {
 
   override componentDidMount() {
     this._renderCanvas();
+    window.addEventListener('profiler-theme-change', this._onThemeChange);
   }
 
+  override componentWillUnmount() {
+    window.removeEventListener('profiler-theme-change', this._onThemeChange);
+  }
+
+  _onThemeChange = () => {
+    this._renderCanvas();
+  };
+
   override componentDidUpdate() {
     this._renderCanvas();
   }

src/components/timeline/Markers.tsx

@@ -237,8 +237,17 @@ class TimelineMarkersCanvas extends React.PureComponent<CanvasProps> {
 
   override componentDidMount() {
     this._scheduleDraw();
+    window.addEventListener('profiler-theme-change', this._onThemeChange);
   }
 
+  override componentWillUnmount() {
+    window.removeEventListener('profiler-theme-change', this._onThemeChange);
+  }
+
+  _onThemeChange = () => {
+    this._scheduleDraw();
+  };
+
   override componentDidUpdate() {
     this._scheduleDraw();
   }

src/test/components/FlameGraph.test.tsx

@@ -66,6 +66,20 @@ describe('FlameGraph', function () {
     expect(drawCalls).toMatchSnapshot();
   });
 
+  it('redraws when the system theme changes', () => {
+    setupFlameGraph();
+    // Flush the initial draw calls.
+    flushDrawLog();
+
+    // Simulate a theme change.
+    window.dispatchEvent(new CustomEvent('profiler-theme-change'));
+
+    // drawCanvasAfterRaf={false} means the redraw is synchronous, so new draw
+    // calls should be available immediately without flushing rAF.
+    const drawCalls = flushDrawLog();
+    expect(drawCalls.length).toBeGreaterThan(0);
+  });
+
   it('ignores invertCallstack and always displays non-inverted', () => {
     const { getState, dispatch } = setupFlameGraph();
     expect(getInvertCallstack(getState())).toBe(false);

src/test/components/SampleGraph.test.tsx

@@ -149,6 +149,21 @@ describe('SampleGraph', function () {
     };
   }
 
+  it('redraws when the system theme changes', () => {
+    const { getContextDrawCalls } = setup();
+
+    // Flush the initial draw calls.
+    getContextDrawCalls();
+
+    // Simulate a theme change.
+    window.dispatchEvent(new CustomEvent('profiler-theme-change'));
+
+    const drawCalls = getContextDrawCalls();
+    expect(drawCalls.some(([operation]) => operation === 'fillRect')).toBe(
+      true
+    );
+  });
+
   it('matches the component snapshot', () => {
     const { sampleGraphCanvas } = setup();
     expect(sampleGraphCanvas).toMatchSnapshot();

src/test/components/ThreadActivityGraph.test.tsx

@@ -170,6 +170,22 @@ describe('ThreadActivityGraph', function () {
     );
   });
 
+  it('redraws when the system theme changes', () => {
+    const { getContextDrawCalls } = setup();
+
+    // Flush out any existing draw calls.
+    getContextDrawCalls();
+    expect(getContextDrawCalls().length).toEqual(0);
+
+    // Simulate a theme change.
+    window.dispatchEvent(new CustomEvent('profiler-theme-change'));
+
+    const drawCalls = getContextDrawCalls();
+    expect(drawCalls.some(([operation]) => operation === 'beginPath')).toBe(
+      true
+    );
+  });
+
   it('matches the 2d canvas draw snapshot with CPU values', () => {
     const profile = getSamplesProfile();
     profile.meta.interval = 1;

src/test/components/TimelineMarkers.test.tsx

@@ -176,6 +176,25 @@ describe('TimelineMarkers', function () {
   beforeEach(addRootOverlayElement);
   afterEach(removeRootOverlayElement);
 
+  it('redraws when the system theme changes', () => {
+    const { flushRafCalls } = setupWithMarkers(
+      { rangeStart: 0, rangeEnd: 10 },
+      [['DOMEvent', 0, 10]]
+    );
+
+    // Flush the initial draw calls.
+    flushRafCalls();
+    flushDrawLog();
+
+    // Simulate a theme change.
+    window.dispatchEvent(new CustomEvent('profiler-theme-change'));
+
+    // _scheduleDraw() uses RAF, so flush it before checking.
+    flushRafCalls();
+    const drawCalls = flushDrawLog();
+    expect(drawCalls.length).toBeGreaterThan(0);
+  });
+
   it('renders correctly overview markers', () => {
     window.devicePixelRatio = 1;
 

src/test/unit/dark-mode.test.ts

@@ -46,6 +46,50 @@ describe('isDarkMode', function () {
   });
 });
 
+describe('profiler-theme-change event', function () {
+  it('is dispatched when the theme changes', function () {
+    resetForTest();
+    // Initialize in light mode.
+    isDarkMode();
+
+    const listener = jest.fn();
+    window.addEventListener('profiler-theme-change', listener);
+
+    // Switch to dark via a storage event.
+    jest.spyOn(Storage.prototype, 'getItem').mockImplementation(() => 'dark');
+    window.dispatchEvent(new StorageEvent('storage', { key: 'theme' }));
+
+    expect(listener).toHaveBeenCalledTimes(1);
+    window.removeEventListener('profiler-theme-change', listener);
+  });
+
+  it('is not dispatched during initialization', function () {
+    resetForTest();
+
+    const listener = jest.fn();
+    window.addEventListener('profiler-theme-change', listener);
+
+    isDarkMode(); // triggers setup
+
+    expect(listener).not.toHaveBeenCalled();
+    window.removeEventListener('profiler-theme-change', listener);
+  });
+
+  it('is not dispatched when the theme stays the same', function () {
+    resetForTest();
+    isDarkMode(); // initialize as light
+
+    const listener = jest.fn();
+    window.addEventListener('profiler-theme-change', listener);
+
+    // Storage event fires but the resolved theme is still light.
+    window.dispatchEvent(new StorageEvent('storage', { key: 'theme' }));
+
+    expect(listener).not.toHaveBeenCalled();
+    window.removeEventListener('profiler-theme-change', listener);
+  });
+});
+
 describe('initTheme', function () {
   it('sets the document element class', function () {
     resetForTest();

src/utils/dark-mode.ts

@@ -40,13 +40,18 @@ function _applyTheme(): void {
     shouldBeDark = getSystemTheme() === 'dark';
   }
 
+  const changed = _isDarkModeSetup && _isDarkMode !== shouldBeDark;
   _isDarkMode = shouldBeDark;
 
   if (shouldBeDark) {
     document.documentElement.classList.add('dark-mode');
   } else {
     document.documentElement.classList.remove('dark-mode');
   }
+
+  if (changed) {
+    window.dispatchEvent(new CustomEvent('profiler-theme-change'));
+  }
 }
 
 export function setThemePreference(pref: ThemePreference): void {