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use crate::core::Size;
use crate::geometry::{self, Frame};
use crate::Cached;
use std::cell::RefCell;
/// 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.
pub struct Cache<Renderer>
where
Renderer: geometry::Renderer,
{
state: RefCell<State<Renderer::Geometry>>,
}
impl<Renderer> Cache<Renderer>
where
Renderer: geometry::Renderer,
{
/// Creates a new empty [`Cache`].
pub fn new() -> Self {
Cache {
state: RefCell::new(State::Empty { previous: None }),
}
}
/// Clears the [`Cache`], forcing a redraw the next time it is used.
pub fn clear(&self) {
use std::ops::Deref;
let previous = match self.state.borrow().deref() {
State::Empty { previous } => previous.clone(),
State::Filled { geometry, .. } => Some(geometry.clone()),
};
*self.state.borrow_mut() = State::Empty { previous };
}
/// Draws geometry using the provided closure and stores it in the
/// [`Cache`].
///
/// The closure will only be called when
/// - the bounds have changed since the previous draw call.
/// - the [`Cache`] is empty or has been explicitly cleared.
///
/// Otherwise, the previously stored geometry will be returned. The
/// [`Cache`] is not cleared in this case. In other words, it will keep
/// returning the stored geometry if needed.
pub fn draw(
&self,
renderer: &Renderer,
bounds: Size,
draw_fn: impl FnOnce(&mut Frame<Renderer>),
) -> Renderer::Geometry {
use std::ops::Deref;
let previous = match self.state.borrow().deref() {
State::Empty { previous } => previous.clone(),
State::Filled {
bounds: cached_bounds,
geometry,
} => {
if *cached_bounds == bounds {
return Cached::load(geometry);
}
Some(geometry.clone())
}
};
let mut frame = Frame::new(renderer, bounds);
draw_fn(&mut frame);
let geometry = frame.into_geometry().cache(previous);
let result = Cached::load(&geometry);
*self.state.borrow_mut() = State::Filled { bounds, geometry };
result
}
}
impl<Renderer> std::fmt::Debug for Cache<Renderer>
where
Renderer: geometry::Renderer,
{
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let state = self.state.borrow();
match *state {
State::Empty { .. } => write!(f, "Cache::Empty"),
State::Filled { bounds, .. } => {
write!(f, "Cache::Filled {{ bounds: {bounds:?} }}")
}
}
}
}
impl<Renderer> Default for Cache<Renderer>
where
Renderer: geometry::Renderer,
{
fn default() -> Self {
Self::new()
}
}
enum State<Geometry>
where
Geometry: Cached,
{
Empty {
previous: Option<Geometry::Cache>,
},
Filled {
bounds: Size,
geometry: Geometry::Cache,
},
}
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