[Feature] Button widget

[vmarcella]

Overview

Add a button widget that responds to mouse clicks and displays text or an icon.

Current State

No response

Scope

Goals:

• Text button with label
• Click detection
• Visual states (normal, hover, pressed, disabled)
• Callback on click

Non-Goals:

• Icon buttons
• Toggle buttons
• Styling

Proposed API

pub enum ButtonState {
  Normal,
  Hovered,
  Pressed,
  Disabled,
}

pub struct Button {
  label: String,
  state: ButtonState,
  on_click: Option<Box<dyn Fn()>>,
}

impl Button {
  pub fn new(label: &str) -> Self;
  pub fn on_click(self, callback: impl Fn() + 'static) -> Self;
  pub fn set_enabled(&mut self, enabled: bool);
  pub fn state(&self) -> ButtonState;
}

impl Widget for Button {
  fn render(&self, ctx: &mut UiRenderContext) -> Vec<RenderCommand>;
  fn hit_test(&self, x: f32, y: f32) -> bool;
  // Mouse event handling internally updates state
}

Acceptance Criteria

• Button displays label text
• Hover state when mouse over
• Pressed state when mouse down
• Click callback fires on mouse up inside
• Disabled state ignores i

Affected Crates

lambda-rs

Notes

• State transitions: Normal <-> Hovered <-> Pressed
• Click fires only if release is inside button