gpui-element

When to Use

Use the low-level Element trait when:

Need fine-grained control over layout calculation
Building complex, performance-critical components
Implementing custom layout algorithms (masonry, circular, etc.)
High-level Render/RenderOnce APIs are insufficient

Prefer Render/RenderOnce for: Simple components, standard layouts, declarative UI

Quick Start

The Element trait provides direct control over three rendering phases:

impl Element for MyElement {
    type RequestLayoutState = MyLayoutState;  // Data passed to later phases
    type PrepaintState = MyPaintState;        // Data for painting

fn id(&self) -> Option<ElementId> {
    Some(self.id.clone())
}

fn source_location(&self) -> Option<&'static std::panic::Location<'static>> {
    None
}

// Phase 1: Calculate sizes and positions
fn request_layout(&mut self, .., window: &mut Window, cx: &mut App)
    -> (LayoutId, Self::RequestLayoutState)
{
    let layout_id = window.request_layout(
        Style { size: size(px(200.), px(100.)), ..default() },
        vec![],
        cx
    );
    (layout_id, MyLayoutState { /* ... */ })
}

// Phase 2: Create hitboxes, prepare for painting
fn prepaint(&mut self, .., bounds: Bounds<Pixels>, layout: &mut Self::RequestLayoutState,
            window: &mut Window, cx: &mut App) -> Self::PrepaintState
{
    let hitbox = window.insert_hitbox(bounds, HitboxBehavior::Normal);
    MyPaintState { hitbox }
}

// Phase 3: Render and handle interactions
fn paint(&mut self, .., bounds: Bounds<Pixels>, layout: &mut Self::RequestLayoutState,
         paint_state: &mut Self::PrepaintState, window: &mut Window, cx: &mut App)
{
    window.paint_quad(paint_quad(bounds, Anchor::all(px(4.)), cx.theme().background));

    window.on_mouse_event({
        let hitbox = paint_state.hitbox.clone();
        move |event: &MouseDownEvent, phase, window, cx| {
            if hitbox.is_hovered(window) && phase.bubble() {
                // Handle interaction
                cx.stop_propagation();
            }
        }
    });
}

}

// Enable element to be used as child impl IntoElement for MyElement { type Element = Self; fn into_element(self) -> Self::Element { self } }


## Core Concepts

### Three-Phase Rendering

1. **request_layout**: Calculate sizes and positions, return layout ID and state
2. **prepaint**: Create hitboxes, compute final bounds, prepare for painting
3. **paint**: Render element, set up interactions (mouse events, cursor styles)

### State Flow

RequestLayoutState → PrepaintState → paint


State flows in one direction through associated types, passed as mutable references between phases.

### Key Operations

- **Layout**: `window.request_layout(style, children, cx)` - Create layout node
- **Hitboxes**: `window.insert_hitbox(bounds, behavior)` - Create interaction area
- **Painting**: `window.paint_quad(...)` - Render visual content
- **Events**: `window.on_mouse_event(handler)` - Handle user input

## Reference Documentation

### Complete API Documentation
- **Element Trait API**: See [api-reference.md](references/api-reference.md)
  - Associated types, methods, parameters, return values
  - Hitbox system, event handling, cursor styles

### Implementation Guides
- **Examples**: See [examples.md](references/examples.md)
  - Simple text element with highlighting
  - Interactive element with selection
  - Complex element with child management

- **Best Practices**: See [best-practices.md](references/best-practices.md)
  - State management, performance optimization
  - Interaction handling, layout strategies
  - Error handling, testing, common pitfalls

- **Common Patterns**: See [patterns.md](references/patterns.md)
  - Text rendering, container, interactive, composite, scrollable patterns
  - Pattern selection guide

- **Advanced Patterns**: See [advanced-patterns.md](references/advanced-patterns.md)
  - Custom layout algorithms (masonry, circular)
  - Element composition with traits
  - Async updates, memoization, virtual lists

About this skill

When to Use

Quick Start