initial transparency

src/shared/windowCapabilities.ts

@@ -4,6 +4,7 @@ interface WindowCapabilityResolutionOptions {
   platform: string
   argv?: readonly string[]
   env?: Record<string, string | undefined>
+  osVersion?: string
 }
 
 export const DEFAULT_WINDOW_CAPABILITIES: WindowCapabilities = {
@@ -11,6 +12,21 @@ export const DEFAULT_WINDOW_CAPABILITIES: WindowCapabilities = {
   useNativeDragRegions: false,
   supportsProgrammaticReposition: true,
   supportsGeometryPersistence: true,
+  supportsBlurredBackground: false,
+}
+
+// Blurred mode uses accent-policy acrylic (SetWindowCompositionAttribute),
+// which technically exists since Windows 10 1803, but drag/repaint performance
+// is only dependable on Windows 11 22H2 (build 22621) — gate it there.
+const WINDOWS_ACRYLIC_MIN_BUILD = 22621
+
+function windowsBuildSupportsAcrylic(osVersion: string | undefined): boolean {
+  if (!osVersion) {
+    return false
+  }
+
+  const build = Number.parseInt(osVersion.split('.')[2] ?? '', 10)
+  return Number.isFinite(build) && build >= WINDOWS_ACRYLIC_MIN_BUILD
 }
 
 function readSwitchValue(argv: readonly string[], switchName: string): string | null {
@@ -80,6 +96,8 @@ export function resolveWindowCapabilities(options: WindowCapabilityResolutionOpt
     return {
       ...DEFAULT_WINDOW_CAPABILITIES,
       useNativeDragRegions: true,
+      supportsBlurredBackground: options.platform === 'darwin'
+        || windowsBuildSupportsAcrylic(options.osVersion),
     }
   }
 
@@ -95,5 +113,6 @@ export function resolveWindowCapabilities(options: WindowCapabilityResolutionOpt
     useNativeDragRegions: isNativeWayland,
     supportsProgrammaticReposition: !isNativeWayland,
     supportsGeometryPersistence: !isNativeWayland,
+    supportsBlurredBackground: false,
   }
 }

src/shared/windowState.ts

@@ -4,8 +4,36 @@ import {
   WINDOW_LOCAL_STATE_FORMAT,
   WINDOW_LOCAL_STATE_VERSION,
   type PrismWindowLocalStateV1,
+  type WindowBackgroundMode,
+  type WindowBackgroundState,
 } from '../types/windowState'
 
+const WINDOW_BACKGROUND_MODES: readonly WindowBackgroundMode[] = ['solid', 'blurred', 'clear']
+
+export function createDefaultWindowBackgroundState(): WindowBackgroundState {
+  return {
+    mode: 'solid',
+    transparency: 50,
+  }
+}
+
+export function normalizeWindowBackgroundState(raw: unknown): WindowBackgroundState {
+  const fallback = createDefaultWindowBackgroundState()
+  if (typeof raw !== 'object' || raw === null) {
+    return fallback
+  }
+
+  const candidate = raw as Partial<WindowBackgroundState>
+  const mode = WINDOW_BACKGROUND_MODES.includes(candidate.mode as WindowBackgroundMode)
+    ? candidate.mode as WindowBackgroundMode
+    : fallback.mode
+  const transparency = typeof candidate.transparency === 'number' && Number.isFinite(candidate.transparency)
+    ? Math.min(100, Math.max(0, Math.round(candidate.transparency)))
+    : fallback.transparency
+
+  return { mode, transparency }
+}
+
 export function createEmptyWindowLocalState(): PrismWindowLocalStateV1 {
   return {
     format: WINDOW_LOCAL_STATE_FORMAT,
@@ -13,6 +41,7 @@ export function createEmptyWindowLocalState(): PrismWindowLocalStateV1 {
     mainAlwaysOnTop: false,
     popoutAlwaysOnTop: {},
     nowPlayingConfigWindowBounds: undefined,
+    windowBackground: createDefaultWindowBackgroundState(),
   }
 }
 
@@ -37,5 +66,6 @@ export function normalizeWindowLocalState(raw: unknown): PrismWindowLocalStateV1
     mainAlwaysOnTop: parsed.mainAlwaysOnTop === true,
     popoutAlwaysOnTop,
     nowPlayingConfigWindowBounds: normalizeWindowBounds(parsed.nowPlayingConfigWindowBounds),
+    windowBackground: normalizeWindowBackgroundState(parsed.windowBackground),
   }
 }