path: root/wgpu/src/widget/canvas/cache.rs

use crate::{
    canvas::{Drawable, Frame, Geometry},
    Primitive,
};

use iced_native::Size;
use std::{cell::RefCell, sync::Arc};

enum State {
    Empty,
    Filled {
        bounds: Size,
        primitive: Arc<Primitive>,
    },
}

impl Default for State {
    fn default() -> Self {
        State::Empty
    }
}
/// A simple cache that stores generated geometry to avoid recomputation.
///
/// A [`Cache`] will not redraw its geometry unless the dimensions of its layer
/// change or it is explicitly cleared.
///
/// [`Layer`]: ../trait.Layer.html
/// [`Cache`]: struct.Cache.html
#[derive(Debug, Default)]
pub struct Cache {
    state: RefCell<State>,
}

impl Cache {
    /// Creates a new empty [`Cache`].
    ///
    /// [`Cache`]: struct.Cache.html
    pub fn new() -> Self {
        Cache {
            state: Default::default(),
        }
    }

    /// Clears the cache, forcing a redraw the next time it is used.
    ///
    /// [`Cached`]: struct.Cached.html
    pub fn clear(&mut self) {
        *self.state.borrow_mut() = State::Empty;
    }

    pub fn draw<T>(&self, new_bounds: Size, input: T) -> Geometry
    where
        T: Drawable + std::fmt::Debug,
    {
        use std::ops::Deref;

        if let State::Filled { bounds, primitive } = self.state.borrow().deref()
        {
            if *bounds == new_bounds {
                return Geometry::from_primitive(primitive.clone());
            }
        }

        let mut frame = Frame::new(new_bounds.width, new_bounds.height);
        input.draw(&mut frame);

        let primitive = Arc::new(frame.into_primitive());

        *self.state.borrow_mut() = State::Filled {
            bounds: new_bounds,
            primitive: primitive.clone(),
        };

        Geometry::from_primitive(primitive)
    }

    pub fn with<'a, T>(&'a self, input: T) -> impl crate::canvas::State + 'a
    where
        T: Drawable + std::fmt::Debug + 'a,
    {
        Bind { cache: self, input }
    }
}

struct Bind<'a, T> {
    cache: &'a Cache,
    input: T,
}

impl<'a, T> crate::canvas::State for Bind<'a, T>
where
    T: Drawable + std::fmt::Debug + 'a,
{
    fn draw(&self, bounds: Size) -> Vec<Geometry> {
        vec![self.cache.draw(bounds, &self.input)]
    }
}

impl std::fmt::Debug for State {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            State::Empty => write!(f, "Empty"),
            State::Filled { primitive, bounds } => f
                .debug_struct("Filled")
                .field("primitive", primitive)
                .field("bounds", bounds)
                .finish(),
        }
    }
}