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Widget

smudge_core::widget

Trait Widget 

Source 
pub trait Widget: Any + TypeName {
    // Required method
    fn paint(&self, cx: &PaintCx<'_>, out: &mut Vec<PaintOp>);

    // Provided methods
    fn measure(&mut self, _input: MeasureInput) -> Option<Size> { ... }
    fn ime_area(&self) -> Option<Rect> { ... }
    fn semantics(&self) -> Option<Semantics> { ... }
}
Expand description

A piece of user interface owned by one tree node.

A widget holds its own state and is the only place that state lives. The tree owns the widget and the Style that positions and paints it.

Implementing this trait requires the type to be 'static, because the tree downcasts to the concrete type when a binding updates a widget property. The TypeName bound is met by every type without any code, and supplies the name of the widget’s type that diagnostics print.

Required Methods§

Source

fn paint(&self, cx: &PaintCx<'_>, out: &mut Vec<PaintOp>)

Appends this widget’s paint operations, in paint coordinates.

Paint coordinates are logical window coordinates with the scroll offsets of the enclosing scroll views left out, so outside a scrolled subtree they are the window’s own. A scroll then moves the operations without asking the widget to paint again.

cx carries the node’s rectangle after layout, in paint coordinates, and its resolved style. Paint this node only: its children paint themselves.

Provided Methods§

Source

fn measure(&mut self, _input: MeasureInput) -> Option<Size>

Returns the size of this widget’s content, or None to let the layout engine size the node from its style.

input.known_width and input.known_height hold the sizes the engine treats as fixed for this call, and either can be absent even when the node’s style fixes a size. input.available_width and input.available_height are the space left on each axis inside the node’s padding and border. An axis can also ask for an intrinsic size instead of offering space: AvailableSpace::MinContent asks for the smallest size the content fits in, such as the widest word of a text, and AvailableSpace::MaxContent asks for the size the content takes without wrapping. The returned size is the content size, so the engine adds padding and border around it.

The engine may call this several times in one layout pass.

The default returns None, which suits a widget that only paints. A widget that returns a size must return the same size for the same inputs, because the layout engine caches it until the node is marked for layout again.

Source

fn ime_area(&self) -> Option<Rect>

Returns the rectangle the input method should anchor to while this widget holds the keyboard focus, in the paint coordinates of Widget::paint.

The app reports the rectangle in window coordinates: it moves the rectangle by minus the scroll offsets that move the widget at the time it asks.

The app asks only the focused widget and reports None when nothing is focused or the widget has no area to report. The default reports None, which suits a widget that takes no text.

Source

fn semantics(&self) -> Option<Semantics>

Returns the accessibility description that places this widget in the projection, or None to leave it out.

The default reports None, which suits a widget that paints for sighted users alone. A widget that returns a description is projected with the role it reports, and an element can still override the role with Element::role.

Dyn Compatibility§

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors§