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//! Write your own renderer.
//!
//! You will need to implement the `Renderer` trait first. It simply contains
//! an `Output` associated type.
//!
//! There is no common trait to draw all the widgets. Instead, every [`Widget`]
//! constrains its generic `Renderer` type as necessary.
//!
//! This approach is flexible and composable. For instance, the
//! [`Text`] widget only needs a [`text::Renderer`] while a [`Checkbox`] widget
//! needs both a [`text::Renderer`] and a [`checkbox::Renderer`], reusing logic.
//!
//! In the end, a __renderer__ satisfying all the constraints is
//! needed to build a [`UserInterface`].
//!
//! [`Widget`]: crate::Widget
//! [`UserInterface`]: crate::UserInterface
//! [`Text`]: crate::widget::Text
//! [`text::Renderer`]: crate::widget::text::Renderer
//! [`Checkbox`]: crate::widget::Checkbox
//! [`checkbox::Renderer`]: crate::widget::checkbox::Renderer
#[cfg(debug_assertions)]
mod null;
#[cfg(debug_assertions)]
pub use null::Null;
use crate::layout;
use crate::{Background, Color, Element, Rectangle, Vector};
/// A component that can take the state of a user interface and produce an
/// output for its users.
pub trait Renderer: Sized {
/// Lays out the elements of a user interface.
///
/// You should override this if you need to perform any operations before or
/// after layouting. For instance, trimming the measurements cache.
fn layout<'a, Message>(
&mut self,
element: &Element<'a, Message, Self>,
limits: &layout::Limits,
) -> layout::Node {
element.layout(self, limits)
}
/// Draws the primitives recorded in the given closure in a new layer.
///
/// The layer will clip its contents to the provided `bounds`.
fn with_layer(&mut self, bounds: Rectangle, f: impl FnOnce(&mut Self));
/// Applies a `translation` to the primitives recorded in the given closure.
fn with_translation(
&mut self,
translation: Vector,
f: impl FnOnce(&mut Self),
);
/// Clears all of the recorded primitives in the [`Renderer`].
fn clear(&mut self);
/// Fills a [`Quad`] with the provided [`Background`].
fn fill_quad(&mut self, quad: Quad, background: impl Into<Background>);
}
/// A polygon with four sides.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Quad {
/// The bounds of the [`Quad`].
pub bounds: Rectangle,
/// The border radius of the [`Quad`].
pub border_radius: f32,
/// The border width of the [`Quad`].
pub border_width: f32,
/// The border color of the [`Quad`].
pub border_color: Color,
}
/// The styling attributes of a [`Renderer`].
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct Style {
/// The text color
pub text_color: Color,
}
impl Default for Style {
fn default() -> Self {
Style {
text_color: Color::BLACK,
}
}
}
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