Support color scheme reporting

CSI ? 996 n
CSI ? 2031 h
CSI ? 2031 l

Fixes #5626

src/browser/CoreBrowserTerminal.ts

@@ -42,7 +42,7 @@ import { SelectionService } from 'browser/services/SelectionService';
 import { ICharSizeService, ICharacterJoinerService, ICoreBrowserService, IKeyboardService, ILinkProviderService, IMouseService, IRenderService, ISelectionService, IThemeService } from 'browser/services/Services';
 import { ThemeService } from 'browser/services/ThemeService';
 import { KeyboardService } from 'browser/services/KeyboardService';
-import { channels, color } from 'common/Color';
+import { channels, color, rgb } from 'common/Color';
 import { CoreTerminal } from 'common/CoreTerminal';
 import * as Browser from 'common/Platform';
 import { ColorRequestType, CoreMouseAction, CoreMouseButton, CoreMouseEventType, IColorEvent, ITerminalOptions, KeyboardResultType, SpecialColorIndex } from 'common/Types';
@@ -252,6 +252,20 @@ export class CoreBrowserTerminal extends CoreTerminal implements ITerminal {
     }
   }
 
+  /**
+   * Reports the current color scheme (dark or light) based on the relative luminance
+   * of the background and foreground theme colors.
+   * Sends CSI ? 997 ; 1 n for dark mode or CSI ? 997 ; 2 n for light mode.
+   */
+  private _reportColorScheme(): void {
+    if (!this._themeService) return;
+    const bgLuminance = rgb.relativeLuminance(this._themeService.colors.background.rgba >> 8);
+    const fgLuminance = rgb.relativeLuminance(this._themeService.colors.foreground.rgba >> 8);
+    // Dark mode = background is darker than foreground (lower luminance)
+    const colorSchemeMode = bgLuminance < fgLuminance ? 1 : 2;
+    this.coreService.triggerDataEvent(`${C0.ESC}[?997;${colorSchemeMode}n`);
+  }
+
   protected _setup(): void {
     super._setup();
 
@@ -495,6 +509,16 @@ export class CoreBrowserTerminal extends CoreTerminal implements ITerminal {
     this._themeService = this._instantiationService.createInstance(ThemeService);
     this._instantiationService.setService(IThemeService, this._themeService);
 
+    // CSI ? 996 n - color scheme query (https://contour-terminal.org/vt-extensions/color-palette-update-notifications/)
+    this._register(this._inputHandler.onRequestColorSchemeQuery(() => this._reportColorScheme()));
+
+    // Emit unsolicited color scheme notification on theme change when DECSET 2031 is enabled
+    this._register(this._themeService.onChangeColors(() => {
+      if (this.coreService.decPrivateModes.colorSchemeUpdates) {
+        this._reportColorScheme();
+      }
+    }));
+
     this._characterJoinerService = this._instantiationService.createInstance(CharacterJoinerService);
     this._instantiationService.setService(ICharacterJoinerService, this._characterJoinerService);
 

src/common/InputHandler.test.ts

@@ -269,6 +269,26 @@ describe('InputHandler', () => {
       inputHandler.resetModePrivate(Params.fromArray([2004]));
       assert.equal(coreService.decPrivateModes.bracketedPasteMode, false);
     });
+    it('should toggle colorSchemeUpdates (DECSET 2031)', () => {
+      const coreService = new MockCoreService();
+      const optionsService = new MockOptionsService();
+      const inputHandler = new TestInputHandler(new MockBufferService(80, 30), new MockCharsetService(), coreService, new MockLogService(), optionsService, new MockOscLinkService(), new MockCoreMouseService(), new MockUnicodeService());
+      // Set color scheme updates mode (default colorSchemeQuery=true)
+      inputHandler.setModePrivate(Params.fromArray([2031]));
+      assert.equal(coreService.decPrivateModes.colorSchemeUpdates, true);
+      // Reset color scheme updates mode
+      inputHandler.resetModePrivate(Params.fromArray([2031]));
+      assert.equal(coreService.decPrivateModes.colorSchemeUpdates, false);
+    });
+    it('should not toggle colorSchemeUpdates when colorSchemeQuery is disabled', () => {
+      const coreService = new MockCoreService();
+      const optionsService = new MockOptionsService();
+      optionsService.rawOptions.vtExtensions = { colorSchemeQuery: false };
+      const inputHandler = new TestInputHandler(new MockBufferService(80, 30), new MockCharsetService(), coreService, new MockLogService(), optionsService, new MockOscLinkService(), new MockCoreMouseService(), new MockUnicodeService());
+      // Attempt to set color scheme updates mode
+      inputHandler.setModePrivate(Params.fromArray([2031]));
+      assert.equal(coreService.decPrivateModes.colorSchemeUpdates, false);
+    });
   });
   describe('regression tests', function (): void {
     function termContent(bufferService: IBufferService, trim: boolean): string[] {

src/common/InputHandler.ts

@@ -159,6 +159,8 @@ export class InputHandler extends Disposable implements IInputHandler {
   public readonly onTitleChange = this._onTitleChange.event;
   private readonly _onColor = this._register(new Emitter<IColorEvent>());
   public readonly onColor = this._onColor.event;
+  private readonly _onRequestColorSchemeQuery = this._register(new Emitter<void>());
+  public readonly onRequestColorSchemeQuery = this._onRequestColorSchemeQuery.event;
 
   private _parseStack: IParseStack = {
     paused: false,
@@ -2026,6 +2028,11 @@ export class InputHandler extends Disposable implements IInputHandler {
         case 2026: // synchronized output (https://github.com/contour-terminal/vt-extensions/blob/master/synchronized-output.md)
           this._coreService.decPrivateModes.synchronizedOutput = true;
           break;
+        case 2031: // color scheme updates (https://contour-terminal.org/vt-extensions/color-palette-update-notifications/)
+          if (this._optionsService.rawOptions.vtExtensions?.colorSchemeQuery ?? true) {
+            this._coreService.decPrivateModes.colorSchemeUpdates = true;
+          }
+          break;
         case 9001: // win32-input-mode (https://github.com/microsoft/terminal/blob/main/doc/specs/%234999%20-%20Improved%20keyboard%20handling%20in%20Conpty.md)
           if (this._optionsService.rawOptions.vtExtensions?.win32InputMode) {
             this._coreService.decPrivateModes.win32InputMode = true;
@@ -2271,6 +2278,11 @@ export class InputHandler extends Disposable implements IInputHandler {
           this._coreService.decPrivateModes.synchronizedOutput = false;
           this._onRequestRefreshRows.fire(undefined);
           break;
+        case 2031: // color scheme updates (https://contour-terminal.org/vt-extensions/color-palette-update-notifications/)
+          if (this._optionsService.rawOptions.vtExtensions?.colorSchemeQuery ?? true) {
+            this._coreService.decPrivateModes.colorSchemeUpdates = false;
+          }
+          break;
         case 9001: // win32-input-mode
           if (this._optionsService.rawOptions.vtExtensions?.win32InputMode) {
             this._coreService.decPrivateModes.win32InputMode = false;
@@ -2774,6 +2786,12 @@ export class InputHandler extends Disposable implements IInputHandler {
         // no dec locator/mouse
         // this.handler(C0.ESC + '[?50n');
         break;
+      case 996:
+        // color scheme query (https://contour-terminal.org/vt-extensions/color-palette-update-notifications/)
+        if (this._optionsService.rawOptions.vtExtensions?.colorSchemeQuery ?? true) {
+          this._onRequestColorSchemeQuery.fire();
+        }
+        break;
     }
     return true;
   }

src/common/TestUtils.test.ts

@@ -106,6 +106,7 @@ export class MockCoreService implements ICoreService {
     applicationCursorKeys: false,
     applicationKeypad: false,
     bracketedPasteMode: false,
+    colorSchemeUpdates: false,
     cursorBlink: undefined,
     cursorStyle: undefined,
     origin: false,

src/common/Types.ts

@@ -268,6 +268,7 @@ export interface IDecPrivateModes {
   applicationCursorKeys: boolean;
   applicationKeypad: boolean;
   bracketedPasteMode: boolean;
+  colorSchemeUpdates: boolean;
   cursorBlink: boolean | undefined;
   cursorStyle: CursorStyle | undefined;
   origin: boolean;

src/common/services/CoreService.ts

@@ -17,6 +17,7 @@ const DEFAULT_DEC_PRIVATE_MODES: IDecPrivateModes = Object.freeze({
   applicationCursorKeys: false,
   applicationKeypad: false,
   bracketedPasteMode: false,
+  colorSchemeUpdates: false,
   cursorBlink: undefined,
   cursorStyle: undefined,
   origin: false,

src/common/services/Services.ts

@@ -313,6 +313,7 @@ export interface IVtExtensions {
   kittyKeyboard?: boolean;
   kittySgrBoldFaintControl?: boolean;
   win32InputMode?: boolean;
+  colorSchemeQuery?: boolean;
 }
 
 export const IOscLinkService = createDecorator<IOscLinkService>('OscLinkService');