fix(overlay): handle X11 display scaling across monitors (#193)

src/core/utils/electron-backend.test.ts

@@ -1,6 +1,6 @@
 import assert from 'node:assert/strict';
 import test from 'node:test';
-import { shouldForceX11ElectronBackend } from './electron-backend';
+import { resolveX11ElectronRelaunchArgs, shouldForceX11ElectronBackend } from './electron-backend';
 
 function withPlatform(platform: NodeJS.Platform, run: () => void): void {
   const original = Object.getOwnPropertyDescriptor(process, 'platform');
@@ -32,3 +32,70 @@ test('shouldForceX11ElectronBackend is false off Linux', () => {
     assert.equal(shouldForceX11ElectronBackend({}), false);
   });
 });
+
+test('resolveX11ElectronRelaunchArgs adds the raw X11 Ozone argument on unsupported Linux', () => {
+  assert.deepEqual(
+    resolveX11ElectronRelaunchArgs(
+      ['--start'],
+      {
+        DISPLAY: ':1',
+        WAYLAND_DISPLAY: 'wayland-0',
+        XDG_CURRENT_DESKTOP: 'KDE',
+      },
+      'linux',
+    ),
+    ['--start', '--ozone-platform=x11'],
+  );
+});
+
+test('resolveX11ElectronRelaunchArgs avoids loops and preserves native Wayland backends', () => {
+  const kdeWayland = {
+    DISPLAY: ':1',
+    WAYLAND_DISPLAY: 'wayland-0',
+    XDG_CURRENT_DESKTOP: 'KDE',
+  };
+  assert.equal(
+    resolveX11ElectronRelaunchArgs(['--start', '--ozone-platform=x11'], kdeWayland, 'linux'),
+    null,
+  );
+  assert.equal(
+    resolveX11ElectronRelaunchArgs(
+      ['--start'],
+      { ...kdeWayland, HYPRLAND_INSTANCE_SIGNATURE: 'hypr' },
+      'linux',
+    ),
+    null,
+  );
+  assert.equal(resolveX11ElectronRelaunchArgs(['--start'], kdeWayland, 'darwin'), null);
+  assert.equal(
+    resolveX11ElectronRelaunchArgs(
+      [],
+      {
+        ...kdeWayland,
+        SUBMINER_APP_ARGC: '1',
+        SUBMINER_APP_ARG_0: '--start',
+      },
+      'linux',
+    )?.at(-1),
+    '--ozone-platform=x11',
+  );
+  assert.equal(
+    resolveX11ElectronRelaunchArgs([], { ...kdeWayland, SUBMINER_X11_BOOTSTRAPPED: '1' }, 'linux'),
+    null,
+  );
+});
+
+test('resolveX11ElectronRelaunchArgs replaces an explicit unsupported Wayland argument', () => {
+  assert.deepEqual(
+    resolveX11ElectronRelaunchArgs(
+      ['--start', '--ozone-platform', 'wayland'],
+      {
+        DISPLAY: ':1',
+        WAYLAND_DISPLAY: 'wayland-0',
+        XDG_CURRENT_DESKTOP: 'KDE',
+      },
+      'linux',
+    ),
+    ['--start', '--ozone-platform=x11'],
+  );
+});

src/core/utils/electron-backend.ts

@@ -4,6 +4,9 @@ import { isSupportedWaylandCompositor } from '../../shared/mpv-x11-backend';
 
 const logger = createLogger('core:electron-backend');
 
+export const X11_ELECTRON_BOOTSTRAP_ENV = 'SUBMINER_X11_BOOTSTRAPPED';
+const X11_ELECTRON_OZONE_ARG = '--ozone-platform=x11';
+
 function getElectronOzonePlatformHint(env: NodeJS.ProcessEnv = process.env): string | null {
   const hint = env.ELECTRON_OZONE_PLATFORM_HINT?.trim().toLowerCase();
   if (hint) return hint;
@@ -24,11 +27,42 @@ function getElectronOzonePlatformHint(env: NodeJS.ProcessEnv = process.env): str
  * Electron Wayland backend is unsupported); the Hyprland/Sway case is left untouched so
  * {@link enforceUnsupportedWaylandMode} can report it.
  */
-export function shouldForceX11ElectronBackend(env: NodeJS.ProcessEnv = process.env): boolean {
-  if (process.platform !== 'linux') return false;
+export function shouldForceX11ElectronBackend(
+  env: NodeJS.ProcessEnv = process.env,
+  platform: NodeJS.Platform = process.platform,
+): boolean {
+  if (platform !== 'linux') return false;
   return !isSupportedWaylandCompositor(env);
 }
 
+export function resolveX11ElectronRelaunchArgs(
+  args: string[],
+  env: NodeJS.ProcessEnv = process.env,
+  platform: NodeJS.Platform = process.platform,
+): string[] | null {
+  if (!shouldForceX11ElectronBackend(env, platform)) return null;
+  if (env[X11_ELECTRON_BOOTSTRAP_ENV] === '1') return null;
+
+  const retainedArgs: string[] = [];
+  let alreadyForced = false;
+  for (let index = 0; index < args.length; index += 1) {
+    const arg = args[index];
+    if (arg === '--ozone-platform') {
+      const value = args[index + 1];
+      alreadyForced = value?.trim().toLowerCase() === 'x11';
+      if (value && !value.startsWith('--')) index += 1;
+      continue;
+    }
+    if (arg?.startsWith('--ozone-platform=')) {
+      alreadyForced = arg.slice('--ozone-platform='.length).trim().toLowerCase() === 'x11';
+      continue;
+    }
+    if (arg) retainedArgs.push(arg);
+  }
+
+  return alreadyForced ? null : [...retainedArgs, X11_ELECTRON_OZONE_ARG];
+}
+
 export function forceX11Backend(args: CliArgs): void {
   if (!shouldStartApp(args)) return;
   if (!shouldForceX11ElectronBackend()) return;