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Input Handling

Input handling bridges OS-level events (from winit, egui, etc.) to DOM-style event dispatch in the tree.

Mouse Input​

Core Functions (in lui/src/interactivity.rs)​

// Hit-tests and updates hover path. Returns true if hover changed.
pub fn pointer_move(tree: &mut Tree, layout: &LayoutBox, pos: (f32, f32)) -> bool;

// Hit-tests, fires on_mouse_down, handles focus, text selection, and form controls.
pub fn mouse_down(tree: &mut Tree, layout: &LayoutBox, pos: (f32, f32),
                  button: MouseButton) -> bool;

// Fires on_mouse_up and synthesises click event.
pub fn mouse_up(tree: &mut Tree, layout: &LayoutBox, pos: (f32, f32),
                button: MouseButton) -> bool;

// With click count for double/triple-click word/line selection
pub fn mouse_down_with_click_count(tree: &mut Tree, layout: &LayoutBox,
    pos: (f32, f32), button: MouseButton, click_count: u8) -> bool;

Mouse Button Types​

pub enum MouseButton { Primary, Secondary, Middle, Other(u8) }

Enter / Leave Synthesis​

pointer_move automatically synthesizes mouseenter/mouseleave events: deepest-first leave on the old hover path, root-first enter on the new hover path.

Hit Testing​

LayoutBox::hit_path((x, y)) returns the deepest element path at a given coordinate. Elements with pointer-events: none are skipped. Hit-test coordinates are in document space (accounting for scroll offsets).

Keyboard Input​

Key Dispatch​

// Bubbles keydown/keyup along the focused element's ancestry
pub fn key_down(tree: &mut Tree, key: &str, code: &str, repeat: bool) -> bool;
pub fn key_up(tree: &mut Tree, key: &str, code: &str) -> bool;

Key and code strings follow DOM conventions: key: "a", code: "KeyA", key: "Enter", code: "Enter".

Focus Management​

tree.focus(path);      // Focus a specific element
tree.blur();           // Remove focus
tree.focus_next(reverse); // Tab/Shift+Tab traversal

Focusable elements: <button>, <a href>, <input> (not hidden), <textarea>, <select>, <summary>, anything with tabindex >= 0. Focus traversal cycles through keyboard-focusable paths in document order, wrapping at ends.

Focus events dispatched: focus → focusin on the new element, blur → focusout on the old element, with related_target carrying the counterpart path.

Modifier Tracking​

pub enum Modifier { Shift, Ctrl, Alt, Meta }

tree.set_modifier(Modifier::Shift, down);

Modifier state is stored on InteractionState::modifiers and accessed during event dispatch.

Text Input​

pub fn text_input(tree: &mut Tree, text: &str);

Inserts text at the focused input's caret position. Supports multibyte UTF-8. Non-text inputs (submit, button, etc.) ignore text input.

Form Control Interaction​

The mouse_down handler includes logic for:

  • Checkbox/radio toggle — click to toggle checked, fires change and input events
  • File input — opens native file dialog via rfd, stores FileInfo (name, size, mime)
  • Color picker — opens color picker overlay
  • Date picker — opens calendar overlay
  • Range slider — drag to adjust value
  • Text editing — click to place caret, drag to select

Scroll Input​

pub fn wheel_event(tree: &mut Tree, x: f32, y: f32,
                   dx: f64, dy: f64, mode: WheelDeltaMode) -> bool;

Scrolls the viewport or the deepest scrollable element under the cursor. Delta mode conversion: pixels → pixels directly, lines → pixels × 40, pages → viewport height.

Runtime API (for winit integration)​

The Runtime<D> abstraction provides unified input methods:

impl<D: Driver> Runtime<D> {
    pub fn on_pointer_move(&mut self, tree: &mut Tree, x: f32, y: f32) -> bool;
    pub fn on_mouse_button(&mut self, tree: &mut Tree, button: MouseButton, pressed: bool) -> bool;
    pub fn on_wheel(&mut self, tree: &mut Tree, pixel_dy: f32, pixel_dx: f32, scale: f32) -> bool;
    pub fn on_key(&mut self, tree: &mut Tree, key: &str, code: &str,
                  pressed: bool, repeat: bool, text: Option<&str>);
    pub fn set_modifier(&self, tree: &mut Tree, modifier: Modifier, down: bool);
    pub fn on_resize(&mut self, tree: &mut Tree, width: u32, height: u32);
    pub fn on_scale_change(&mut self);
}