Desktop Principles

Version-sensitive. Every API name, SDK gate and browser-support claim below was verified on 2026-09-08 against primary sources. What against, and when, is in _jutsu/VERSIONS.md. If that date is old, re-verify before acting on a version number.

Desktop Principles

Desktop UX context. Loaded when desktop is detected (macOS, Windows, Linux desktop, web desktop). Concise rules here. Deep-dive in references/.

Hover States Are Mandatory

Hover is the primary affordance signal on desktop, the inverse of mobile. A pointer hovering over a target without immediate visual feedback feels broken: users rely on :hover to confirm an element is interactive before committing to a click. Every clickable surface must have a distinct hover style, ideally with a 100-200ms transition so the change is perceptible without feeling sluggish.

CSS - hover styles for interactive elements:

.button {
  background: var(--surface);
  transition: background 120ms ease-out, transform 120ms ease-out;
}

.button:hover {
  background: var(--surface-hover);
  transform: translateY(-1px);
}

.button:active {
  transform: translateY(0);
}

SwiftUI - `.onHover` is the portable hover signal; `.hoverEffect` is iOS/iPadOS-only and must be `#if`-gated:

struct ToolbarButton: View {
  @State private var hovering = false

  var body: some View {
    Image(systemName: "square.and.arrow.up")
      .padding(8)
      .background(hovering ? Color.gray.opacity(0.15) : .clear)
      .onHover { hovering = $0 }
      .animation(.easeOut(duration: 0.12), value: hovering)
      .pointerHighlight() // see the extension below - .hoverEffect is UNAVAILABLE on macOS
  }
}

// `.hoverEffect` is @available(macOS, unavailable). Gate it with #if, never with #available.
extension View {
  @ViewBuilder func pointerHighlight() -> some View {
    #if os(macOS)
    self
    #else
    self.hoverEffect(.highlight)
    #endif
  }
}

Compose Desktop - onPointerEvent or hoverable + interactionSource:

@OptIn(ExperimentalComposeUiApi::class)
@Composable
fun ToolbarButton(onClick: () -> Unit) {
  val interactionSource = remember { MutableInteractionSource() }
  val hovered by interactionSource.collectIsHoveredAsState()

  Box(
    modifier = Modifier
      .hoverable(interactionSource)
      .background(if (hovered) Color.LightGray.copy(alpha = 0.15f) else Color.Transparent)
      .clickable(onClick = onClick)
      .padding(8.dp),
  ) { Icon(Icons.Default.Share, contentDescription = "Share") }
}

Pointer Precision

Mouse and trackpad pointers are far more accurate than thumbs, so desktop targets can be smaller than the 44pt mobile minimum. Common ranges are 24-32px for icon buttons, 28-36px for toolbar items. WCAG 2.5.8 Target Size (Minimum), Level AA, sets the floor at 24x24 CSS pixels for all pointer input - it is not desktop-specific. A sub-24px target still passes under the spacing exception: draw a 24px-diameter circle centred on each undersized target and no two circles may intersect. Apple's macOS HIG is stricter in spirit and looser in numbers: 28x28 pt default control size, 20x20 pt absolute minimum.

Fitts's Law in practice: the time to acquire a target shrinks with size and grows with distance. Screen edges and corners are infinite-depth targets - the cursor stops there regardless of overshoot. Put high-frequency global controls (close window, system menu, app dock) in corners and along edges. macOS menubar and Windows taskbar are textbook applications: edge-anchored, zero-overshoot acquisition.

Keyboard Shortcuts (first-class)

Desktop users expect parity with native conventions. Missing ⌘+F in a list-heavy app is not minimalism, it is a bug.

Web - detect Ctrl vs Cmd correctly:

// Prefer event.metaKey on macOS, event.ctrlKey elsewhere.
// navigator.platform is deprecated but still pragmatic; fall back to userAgent.
// navigator.platform is always a non-empty string where it exists, so `||` never falls through.
// Prefer UA-CH where available, then platform, then the UA string.
const isMac = /Mac|iPhone|iPad/.test(
  navigator.userAgentData?.platform ?? navigator.platform ?? navigator.userAgent ?? ""
);

window.addEventListener("keydown", (e) => {
  const cmdOrCtrl = isMac ? e.metaKey : e.ctrlKey;
  if (cmdOrCtrl && e.key.toLowerCase() === "k") {
    e.preventDefault();
    openCommandPalette();
  }
});

SwiftUI - .keyboardShortcut binds to menu commands:

Button("New Document", action: newDoc)
  .keyboardShortcut("n", modifiers: .command)

Button("Find", action: focusSearch)
  .keyboardShortcut("f", modifiers: .command)

Compose Desktop - onKeyEvent + KeyShortcut:

@OptIn(ExperimentalComposeUiApi::class)
fun Modifier.commandShortcut(key: Key, onTrigger: () -> Unit) =
  onKeyEvent { event ->
    if (event.type == KeyEventType.KeyDown && event.isMetaPressed && event.key == key) {
      onTrigger(); true
    } else false
  }

// In MenuBar:
MenuBar {
  Menu("File") {
    Item("New", shortcut = KeyShortcut(Key.N, meta = true), onClick = ::newDoc)
    Item("Find", shortcut = KeyShortcut(Key.F, meta = true), onClick = ::focusSearch)
  }
}

Multi-Window Patterns

Desktop users keep windows side by side. A new window is the right answer when:

• A task runs long enough that the user wants to keep working in the main window (rendering, export, sync log).
• The user is comparing two parallel contexts (two documents, two chats, two issues).
• The app is document-based and each document is a peer (Pages, Figma files, Xcode projects).

A new window is the wrong answer for transient confirmations, brief settings panels, or anything that can live in a sheet or popover.

SwiftUI - WindowGroup for document-style, Window for singletons:

@main
struct MyApp: App {
  var body: some Scene {
    WindowGroup("Document") { DocumentView() } // peer windows, one per doc

    Window("Inspector", id: "inspector") { InspectorView() }
      .windowResizability(.contentSize) // tracks intrinsic content size

    Settings { SettingsView() } // ⌘+, target on macOS
  }
}

Compose Desktop - Window composables, application scope:

fun main() = application {
  val docs = remember { mutableStateListOf(Document()) }

  docs.forEach { doc ->
    Window(onCloseRequest = { docs.remove(doc) }, title = doc.title) {
      DocumentView(doc)
    }
  }

  if (showInspector) {
    Window(onCloseRequest = { showInspector = false }, title = "Inspector") {
      InspectorView()
    }
  }
}

State sharing: windows are views over the same model. Hold the source of truth in a singleton or a DI-scoped object (SwiftUI @Observable injected via environment, Compose koin or viewModel-equivalent). Never duplicate state per window - reconciling diverging copies is a graveyard of bugs.

Focus Management