swiftui-liquid-glass

# SwiftUI Liquid Glass

Liquid Glass is the dynamic translucent material introduced in iOS 26 (and iPadOS 26,
macOS 26, tvOS 26, watchOS 26). It blurs content behind it, reflects surrounding color
and light, and reacts to touch and pointer interactions. Standard SwiftUI components
(tab bars, toolbars, navigation bars, sheets) adopt Liquid Glass automatically when
built with the iOS 26 SDK. Use the APIs below for custom views and controls.

See [references/liquid-glass.md](references/liquid-glass.md) for the full API reference with additional examples.

## Contents

- [Workflow](#workflow)
- [Core API Summary](#core-api-summary)
- [Code Examples](#code-examples)
- [Common Mistakes](#common-mistakes)
- [Review Checklist](#review-checklist)
- [References](#references)

## Workflow

Choose the path that matches the request:

### 1. Implement a new feature with Liquid Glass

1. Identify target surfaces (cards, chips, floating controls, custom bars).
2. Decide shape, prominence, and whether each element needs interactivity.
3. Wrap grouped glass elements in a `GlassEffectContainer`.
4. Apply `.glassEffect()` **after** layout and appearance modifiers.
5. Add `.interactive()` only to tappable/focusable elements.
6. Add morphing transitions with `glassEffectID(_:in:)` where the view hierarchy
   changes with animation.
7. Gate with `if #available(iOS 26, *)` and provide a fallback for earlier versions.

### 2. Improve an existing feature with Liquid Glass

1. Find custom blur/material backgrounds that can be replaced with `.glassEffect()`.
2. Wrap sibling glass elements in `GlassEffectContainer` for blending and performance.
3. Replace custom glass-like buttons with `.buttonStyle(.glass)` or `.buttonStyle(.glassProminent)`.
4. Add morphing transitions where animated insertion/removal occurs.

### 3. Review existing Liquid Glass usage

Run through the Review Checklist below and verify each item.

## Core API Summary

### glassEffect(_:in:)

Applies Liquid Glass behind a view. Default: `.regular` variant in a `Capsule` shape.

```swift
nonisolated func glassEffect(
    _ glass: Glass = .regular,
    in shape: some Shape = DefaultGlassEffectShape()
) -> some View
```

### Glass struct

| Property / Method | Purpose |
|---|---|
| `.regular` | Standard glass material |
| `.clear` | Clear variant (minimal tint) |
| `.identity` | No visual effect (pass-through) |
| `.tint(_:)` | Add a color tint for prominence |
| `.interactive(_:)` | React to touch and pointer interactions |

Chain them: `.regular.tint(.blue).interactive()`

### GlassEffectContainer

Wraps multiple glass views for shared rendering, blending, and morphing.

```swift
GlassEffectContainer(spacing: 24) {
    // child views with .glassEffect()
}
```

The `spacing` controls when nearby glass shapes begin to blend. Match or exceed
the interior layout spacing so shapes merge during animated transitions but remain
separate at rest.

### Morphing & Transitions

| Modifier | Purpose |
|---|---|
| `glassEffectID(_:in:)` | Stable identity for morphing during view hierarchy changes |
| `glassEffectUnion(id:namespace:)` | Merge multiple views into one glass shape |
| `glassEffectTransition(_:)` | Control how glass appears/disappears |

Transition types: `.matchedGeometry` (default when within spacing), `.materialize`
(fade content + animate glass in/out), `.identity` (no transition).

### Button Styles

```swift
Button("Action") { }
    .buttonStyle(.glass)           // standard glass button

Button("Primary") { }
    .buttonStyle(.glassProminent)  // prominent glass button
```

### Scroll Edge Effects and Background Extension (iOS 26+)

These complement Liquid Glass when building custom toolbars and scroll views:

```swift
ScrollView {
    content
}
.scrollEdgeEffectStyle(.soft, for: .top)  // Configures edge effect at scroll boundaries

// Duplicate view into mirrored copies at safe area edges with blur (e.g., under sidebars)
content
    .backgroundExtensionEffect()
```

### ToolbarSpacer (iOS 26+)

Creates a visual break between items in toolbars:

```swift
.toolbar {
    ToolbarItem { Button("Edit") { } }
    ToolbarSpacer(.fixed)
    ToolbarItem { Button("Share") { } }
}
```

## Code Examples

### Basic glass effect with availability gate

```swift
if #available(iOS 26, *) {
    Text("Status")
        .padding()
        .glassEffect(.regular.interactive(), in: .rect(cornerRadius: 16))
} else {
    Text("Status")
        .padding()
        .background(.ultraThinMaterial, in: RoundedRectangle(cornerRadius: 16))
}
```

### Grouped glass elements in a container

```swift
GlassEffectContainer(spacing: 24) {
    HStack(spacing: 24) {
        ForEach(tools) { tool in
            Image(systemName: tool.icon)
                .frame(width: 56, height: 56)
                .glassEffect(.regular.interactive())
        }
    }
}
```

### Morphing transition

```swift
@State private var isExpanded = false
@Namespace private var ns

var body: some View {
    GlassEffectContainer(spacing: 40) {
        HStack(spacing: 40) {
            Image(systemName: "pencil")
                .frame(width: 80, height: 80)
                .glassEffect()
                .glassEffectID("pencil", in: ns)

            if isExpanded {
                Image(systemName: "eraser.fill")
                    .frame(width: 80, height: 80)
                    .glassEffect()
                    .glassEffectID("eraser", in: ns)
            }
        }
    }

    Button("Toggle") {
        withAnimation { isExpanded.toggle() }
    }
    .buttonStyle(.glass)
}
```

### Unioning views into a single glass shape

```swift
@Namespace private var ns

GlassEffectContainer(spacing: 20) {
    HStack(spacing: 20) {
        ForEach(items.indices, id: \.self) { i in
            Image(systemName: items[i])
                .frame(width: 80, height: 80)
                .glassEffect()
                .glassEffectUnion(id: i < 2 ? "group1" : "group2", namespace: ns)
        }
    }
}
```

### Tinted glass ba