liquid-glass

What this skill does

# Liquid Glass Design

Build native macOS/iOS applications with Apple's Liquid Glass design and HIG.

## Core Rules

### Three-Layer Model

```
┌─────────────────────────────────────────┐
│     GLASS LAYER (Navigation/Controls)   │  ← Glass here ONLY
├─────────────────────────────────────────┤
│         CONTENT LAYER (Your App)        │  ← Never glass here
└─────────────────────────────────────────┘
```

Glass is ONLY for navigation floating above content. Never on content itself.

### Five Principles

1. **Content First** - Glass floats above, content shines through
2. **Depth Through Light** - Lensing creates hierarchy, not opacity
3. **Adaptive Tinting** - Colors respond to background dynamically
4. **Semantic Emphasis** - Tint primary actions only
5. **Accessibility Built-In** - System handles adaptations automatically

## Materials (macOS 14+ / Pre-iOS 26)

```swift
// Card with material
.padding(24)
.background(.regularMaterial, in: RoundedRectangle(cornerRadius: 16, style: .continuous))

// Material options (lightest → heaviest):
// .ultraThinMaterial, .thinMaterial, .regularMaterial (default), .thickMaterial, .ultraThickMaterial
```

## Liquid Glass API (iOS 26+ / macOS Tahoe)

```swift
// Basic
Button("Action") { }.glassEffect()

// Variants
.glassEffect(.regular)   // Standard UI
.glassEffect(.clear)     // Media backgrounds only
.glassEffect(.identity)  // Disabled

// Interactive (adds bounce/shimmer)
Button("Tap") { }.glassEffect(.regular.interactive())

// Multiple glass elements - MUST wrap in container
GlassEffectContainer(spacing: 30) {
    HStack {
        Button("A") { }.glassEffect()
        Button("B") { }.glassEffect()
    }
}

// Button styles
Button("Cancel") { }.buttonStyle(.glass)           // Secondary
Button("Save") { }.buttonStyle(.glassProminent).tint(.blue)  // Primary
```

## Essential Patterns

### Card

```swift
VStack(alignment: .leading, spacing: 12) {
    HStack {
        ZStack {
            Circle().fill(color.opacity(0.15)).frame(width: 36, height: 36)
            Image(systemName: icon).foregroundStyle(color)
        }
        Spacer()
    }
    Text(value).font(.system(size: 28, weight: .bold, design: .rounded))
    Text(label).font(.caption).foregroundStyle(.secondary)
}
.padding(20)
.background(.regularMaterial, in: RoundedRectangle(cornerRadius: 16, style: .continuous))
```

### Row with Hover

```swift
HStack { content }
.padding(16)
.background(isHovering ? Color.primary.opacity(0.04) : .clear)
.background(.quaternary.opacity(0.5), in: RoundedRectangle(cornerRadius: 12, style: .continuous))
.onHover { withAnimation(.easeInOut(duration: 0.15)) { isHovering = $0 } }
```

### Badge

```swift
HStack(spacing: 8) {
    Circle().fill(isActive ? .green : .orange).frame(width: 8, height: 8)
    Text(status).font(.caption).fontWeight(.medium)
}
.padding(.horizontal, 12).padding(.vertical, 8)
.background(.regularMaterial, in: Capsule())
```

### Icon with Tinted Background

```swift
ZStack {
    Circle().fill(color.opacity(0.15)).frame(width: 32, height: 32)
    Image(systemName: icon).font(.system(size: 14, weight: .semibold)).foregroundStyle(color)
}
```

## Shapes

```swift
// Always use .continuous
RoundedRectangle(cornerRadius: 16, style: .continuous)  // Cards
RoundedRectangle(cornerRadius: 12, style: .continuous)  // Rows
RoundedRectangle(cornerRadius: 8, style: .continuous)   // Small elements
Capsule()  // Pills, badges
Circle()   // Icons
```

## Colors

```swift
// Semantic foreground
.foregroundStyle(.primary)    // Main content
.foregroundStyle(.secondary)  // Subtitles
.foregroundStyle(.tertiary)   // Timestamps

// Backgrounds
.background(.quaternary)
.background(.quaternary.opacity(0.5))

// Accent meanings
Color.blue    // Primary actions, selection
Color.green   // Success, active
Color.orange  // Warning, loading
Color.red     // Destructive, error
Color.purple  // Premium, AI
Color.cyan    // Security

// Tinted backgrounds: always 15% opacity
.fill(color.opacity(0.15))
```

## Typography

```swift
.font(.largeTitle).fontWeight(.bold)      // Page titles
.font(.headline).fontWeight(.semibold)    // Section headers
.font(.subheadline).fontWeight(.medium)   // Row titles
.font(.body)                               // Content (17pt default)
.font(.caption)                            // Metadata
.font(.caption2)                           // Timestamps
.font(.system(size: 28, weight: .bold, design: .rounded))  // Stats
```

**Rules:** Min 11pt. Avoid Ultralight/Thin/Light. Use system fonts for Dynamic Type.

## Spacing (8pt Grid)

```swift
// Standard values: 4, 8, 12, 16, 20, 24, 32, 40, 48

.padding(24)                    // Cards
.padding(16)                    // Rows
.padding(.horizontal, 12).padding(.vertical, 8)  // Badges

// Rule: external spacing ≥ internal spacing
VStack(spacing: 24) { CardView().padding(20) }  // Correct
```

## SF Symbols

```swift
// Preferred: hierarchical for depth
Image(systemName: icon).symbolRenderingMode(.hierarchical).foregroundStyle(color)

// Match weight to nearby text
Image(systemName: "gear").font(.system(size: 14, weight: .semibold))
```

## Hit Targets

```swift
// MINIMUM: 44pt × 44pt
Button { } label: { Image(systemName: "gear") }
    .frame(minWidth: 44, minHeight: 44)
```

## Animations

```swift
// Hover
.onHover { withAnimation(.easeInOut(duration: 0.15)) { isHovering = $0 } }

// Spring
withAnimation(.spring(response: 0.3)) { }
withAnimation(.bouncy) { }

// Entry
.opacity(appeared ? 1 : 0).offset(y: appeared ? 0 : 10)
.onAppear { withAnimation(.spring(response: 0.5, dampingFraction: 0.8)) { appeared = true } }
```

## Do's and Don'ts

**DO:**
- Use `.regularMaterial` for cards/toolbars
- Use `.continuous` on ALL rounded rectangles
- Use 15% opacity for icon backgrounds
- Wrap multiple glass in `GlassEffectContainer`
- Use 44pt minimum hit targets
- Use 8pt grid spacing
- Use SF Symbols with `.hierarchical`

**DON'T:**
- Apply glass to content (lists, tables)
- Stack glass on glass without container
- Use sharp corners
- Go below 11pt text
- Create touch targets < 44pt
- Use full-color images on glass

## Accessibility

System handles automatically:
- Reduce Transparency → opaquer glass
- Increase Contrast → visible borders
- Reduce Motion → no bouncy effects
- Dynamic Type → text scales

Manual override if needed:
```swift
@Environment(\.accessibilityReduceTransparency) var reduceTransparency
.glassEffect(reduceTransparency ? .identity : .regular)
```

## References

For detailed patterns and examples, see:
- [references/components.md](references/components.md) - Full component implementations
- [references/apple-hig.md](references/apple-hig.md) - Complete Apple HIG guidelines