coffee 0.4.1

An opinionated 2D game engine focused on simplicity, explicitness, and type-safety
Documentation 
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use crate::graphics::Point;
use crate::ui::core::{Event, Hasher, Layout, MouseCursor, Node};

/// A component that displays information or allows interaction.
///
/// If you want to build a custom widget, you will need to implement this trait.
/// Additionally, remember to also provide [`Into<Element>`] so your users can
/// easily turn your [`Widget`] into a generic [`Element`]
///
/// [`Into<Element>`]: struct.Element.html
/// [`Widget`]: trait.Widget.html
/// [`Element`]: struct.Element.html
pub trait Widget<Message, Renderer>: std::fmt::Debug {
    /// Returns the [`Node`] of the [`Widget`].
    ///
    /// This [`Node`] is used by the runtime to compute the [`Layout`] of the
    /// user interface.
    ///
    /// [`Node`]: struct.Node.html
    /// [`Widget`]: trait.Widget.html
    /// [`Layout`]: struct.Layout.html
    fn node(&self, renderer: &Renderer) -> Node;

    /// Draws the [`Widget`] using the associated `Renderer`.
    ///
    /// It must return the [`MouseCursor`] state for the [`Widget`].
    ///
    /// [`Widget`]: trait.Widget.html
    /// [`MouseCursor`]: enum.MouseCursor.html
    fn draw(
        &self,
        renderer: &mut Renderer,
        layout: Layout<'_>,
        cursor_position: Point,
    ) -> MouseCursor;

    /// Computes the _layout_ hash of the [`Widget`].
    ///
    /// The produced hash is used by the runtime to decide if the [`Layout`]
    /// needs to be recomputed between frames. Therefore, to ensure maximum
    /// efficiency, the hash should only be affected by the properties of the
    /// [`Widget`] that can affect layouting.
    ///
    /// For example, the [`Text`] widget does not hash its color property, as
    /// its value cannot affect the overall [`Layout`] of the user interface.
    ///
    /// [`Widget`]: trait.Widget.html
    /// [`Layout`]: struct.Layout.html
    /// [`Text`]: ../widget/text/struct.Text.html
    fn hash(&self, state: &mut Hasher);

    /// Processes a runtime [`Event`].
    ///
    /// It receives:
    ///   * an [`Event`] describing user interaction
    ///   * the computed [`Layout`] of the [`Widget`]
    ///   * the current cursor position
    ///   * a mutable `Message` vector, allowing the [`Widget`] to produce
    ///   new messages based on user interaction.
    ///
    /// By default, it does nothing.
    ///
    /// [`Event`]: enum.Event.html
    /// [`Widget`]: trait.Widget.html
    /// [`Layout`]: struct.Layout.html
    fn on_event(
        &mut self,
        _event: Event,
        _layout: Layout<'_>,
        _cursor_position: Point,
        _messages: &mut Vec<Message>,
    ) {
    }
}